Db2 glossary

This glossary provides terms and definitions for the Db2 for z/OS software and products.

The following cross-references are used in this glossary:

See refers you from a nonpreferred term to the preferred term or from an abbreviation to the spelled-out form.
See also refers you to a related or contrasting term.

Numerics A B C D E F G H I J K L M N O P Q R S T U V W X Z

Numerics

6-byte format: The format of table spaces and index pages that supports a 6-byte relative byte address and log record sequence number.

A

abend: See abnormal end of task.
abend reason code: A 4-byte hexadecimal code that uniquely identifies a problem with a program that runs on the z/OS operating system.
abnormal end of task (abend): The termination of a task, job, or subsystem because of an error condition that recovery facilities cannot resolve during execution.
access method services (AMS): A multifunction utility named IDCAMS that is used to manage catalogs, devices, and both VSAM and non-VSAM data sets.
access path: The method that is selected by the database manager for retrieving data from a specific table. For example, an access path can involve the use of an index, a sequential scan, or a combination of the two.
access path stability: A characteristic of an access path that defines reliability for dynamic or static queries. Access paths are not regenerated unless there is a schema change or manual intervention.
active log: A data set with a fixed size where recovery events are recorded as they occur. When the active log is full, the contents of the active log are copied to the archive log.
address space: The range of addresses available to a computer program or process. Address space can refer to physical storage, virtual storage, or both. See also allied address space, buffer pool.
address space connection: The result of connecting an allied address space to Db2. See also allied address space, task control block.
address space identifier (ASID): A unique, system-assigned identifier for an address space.
after trigger: A trigger that is specified to be activated after a defined trigger event (an insert, an update, or a delete operation on the table that is specified in a trigger definition). See also before trigger, instead of trigger, trigger, trigger activation, trigger activation time.
agent: In a z/OS environment, the structure that associates all processes that are involved in a unit of work.
aggregate function: A function that optionally accepts arguments and returns a single scalar value that is the result of an evaluation of a set of like values, such as those in a column within a set of one or more rows. See also function, routine.
alias: An alternative name used to identify a database, a module, a nickname, a sequence, a table, a view, or another alias. An alias can be used in SQL statements to refer to an object in the same Db2 system or subsystem or in a remote Db2 system or subsystem. See also database alias, public alias.
allied address space: An area of storage that is external to Db2 and that is connected to Db2. An allied address space can request Db2 services. See also address space, address space connection.
allied agent: An agent that represents work requests that originate in allied address spaces. See also system agent.
allied thread: A thread that originates at the local Db2 for z/OS subsystem and that can access data at a remote Db2 for z/OS subsystem.
allocated cursor: A cursor that is defined for procedure result sets by using the SQL statement ALLOCATE CURSOR.
ambiguous cursor: A database cursor for which Db2 cannot determine whether it is used for update or read-only purposes.
American Standard Code for Information Interchange (ASCII): A standard code that is used for information exchange among data processing systems, data communication systems, and associated equipment. ASCII uses a coded character set consisting of 7-bit coded characters. See also Extended Binary Coded Decimal Interchange Code.
AMS: See access method services.
AP: See application process.
APAR: See authorized program analysis report.
APF: See authorized program facility.
API: See application programming interface.
application: One or more computer programs or software components that provide a function in direct support of a specific business process or processes.
application period: A pair of columns with application-maintained values that indicates the period of time when a row is valid. See also application-period temporal table.
application-period temporal table: A table that includes an application period. See also application period, bitemporal table.
application plan: The control structure that is produced during the bind process. Db2 for z/OS uses an application plan to run SQL statements.
application process (AP): A unit to which resources and locks are allocated. An application process involves the running of one or more programs.
application programming interface (API): An interface that allows an application program that is written in a high-level language to use specific data or functions of the operating system or another program.
archive-enabled table: A table that has an associated archive table. When rows are deleted from an archive-enabled table, Db2 can automatically insert the old rows into an archive table.
archive log: The set of log files that are closed and are no longer needed for normal processing. These files are retained for use in rollforward recovery.
archive table: A table that is used to store archived rows from another table, which is called an archive-enabled table.
array: A structure that contains an ordered collection of elements of the same data type in which each element can be referenced by its index value or ordinal position in the collection. See also element, ordinary array.
ASCII: See American Standard Code for Information Interchange.
ASID: See address space identifier.
associative array: An array with no user-defined upper boundary on the number of elements, which are ordered by and can be referenced by an array index value. Array index values are unique and do not have to be contiguous. See also ordinary array.
attachment facility: An interface between Db2 and TSO, IMS, CICS, or batch address spaces. An attachment facility allows application programs to access Db2.
attribute: A characteristic or trait of an entity that describes the entity; for example, the telephone number of an employee is one of the employee attributes. See also element.
authorization ID: See authorization identifier.
authorization identifier (authorization ID): A character string that designates a set of privileges and can be used to verify authority. An authorization ID can represent an object, an individual user, an organizational group, a function, or a database role.
authorized program analysis report (APAR): A request for correction of a defect in a supported release of a program supplied by IBM.
authorized program facility (APF): In a z/OS environment, a facility that permits the identification of programs that are authorized to use restricted functions.
autobind phase-in: A phase-in rebind for packages marked with statement-level invalidation. Packages with invalid statements can be allocated, and valid statements can execute without waiting for the rebind to complete. Invalid statements must go through incremental bind before they execute. See also automatic bind, phase-in rebind.
automatic bind: A process by which SQL statements are bound automatically (without a user issuing a BIND command) when an application process begins execution and the bound application plan or package it requires is not valid. See also dynamic bind, static bind.
automatic query rewrite: A process that examines an SQL statement that refers to one or more base tables, and, if appropriate, rewrites the statement so that the query performs better.
auxiliary index: An index on an auxiliary table in which each index entry refers to a LOB or XML document.
auxiliary table: A table that stores columns outside the table in which they are defined. See also base table.

B

backout: The process of undoing uncommitted changes that an application process has made. A backout might be necessary if part of an application process fails or as a result of a deadlock situation. See also roll back.
backward log recovery: The final phase of restart processing during which Db2 scans the log in a backward direction to apply UNDO log records for all aborted changes.
base table: A table that is created by the SQL CREATE TABLE statement and that holds persistent data. See also auxiliary table, clone table, created temporary table, declared temporary table, result table, table, temporary table, view.
base table space: A table space that contains base tables.
basic predicate: A predicate that compares two values.
basic row format: A row format in which values for columns are stored in the row in the order in which the columns are defined by the CREATE TABLE statement. See also reordered row format.
basic sequential access method (BSAM): An access method for storing or retrieving data blocks in a continuous sequence, that uses either a sequential access or a direct-access device.
before trigger: A trigger that is specified to be activated before a defined trigger event (an insert, an update, or a delete operation on the table that is specified in a trigger definition). See also after trigger, instead of trigger, trigger, trigger activation, trigger activation time.
begin column: In a system period or an application period, the column that indicates the beginning of the period. See also period.
binary large object (BLOB): A data type whose value is a sequence of bytes that can range in size from 0 bytes to 2 gigabytes less 1 byte. This sequence does not have an associated code page and character set. BLOBs can contain, for example, image, audio, or video data. See also large object.
binary string: A sequence of bytes that is not associated with a CCSID. For example, the BLOB data type is a binary string. See also coded character set identifier.
binary XML format: A representation of XML data that uses binary values, an approach that facilitates more efficient storage and exchange.
bind: A process by which a usable control structure with SQL statements is generated; the structure is often called an access plan, an application plan, or a package. During this bind process, access paths to the data are selected, and some authorization checking is performed.
bit data: Data with character type CHAR or VARCHAR that is not associated with a coded character set and therefore is never converted.
bitemporal table: A table that is both a system-period temporal table and an application-period temporal table. See also application-period temporal table, system-period temporal table.
BLOB: See binary large object.
block fetch: A function of the Db2 database that retrieves (or fetches) a set of rows together. Using a block fetch can significantly reduce the number of messages that are sent across the network. Block fetch applies only to cursors that do not update data.
bootstrap data set (BSDS): A VSAM data set that contains name and status information for Db2 for z/OS and relative-byte address-range specifications for all active and archive log data sets. It also contains passwords for the Db2 for z/OS directory and catalog and lists of conditional restart and checkpoint records.
BSAM: See basic sequential access method.
BSDS: See bootstrap data set.
buffer pool: An area of memory into which data pages are read and in which they are modified and held during processing. See also address space.
built-in data type: A data type that IBM supplies. Among the built-in data types for Db2 for z/OS are string, numeric, XML, ROWID, and datetime. See also distinct type.
built-in function: A function that is defined by the database manager. See also function, routine, user-defined function.
built-in global variable: A global variable that is defined by the database manager. See also special register, user-defined global variable.
business dimension: A category of data, such as products or time periods, that an organization might want to analyze. See also multidimensional analysis.

C

cache structure

A coupling facility structure that stores data that can be available to all members of a sysplex. A Db2 data sharing group uses cache structures as group buffer pools. See also group buffer pool.

CAF

See call attachment facility.

call attachment facility (CAF)

A Db2 for z/OS attachment facility for application programs that run in TSO or z/OS batch. The CAF is an alternative to the DSN command processor and provides greater control over the execution environment. See also Resource Recovery Services attachment facility.

call level interface

A callable application programming interface (API) for database access, which is an alternative to using embedded SQL.

cascade delete

A process by which the Db2 database manager enforces referential constraints by deleting all descendent rows of a deleted parent row.

CASE expression

An expression that is selected based on the evaluation of one or more conditions.

cast function

A function that is used to convert instances of a source data type into instances of a different target data type. In general, a cast function has the name of the target data type and has one single argument whose type is the source data type. Its return type is the target data type.

castout

The process of writing changed pages from a group buffer pool to disk.

castout owner

The Db2 member that is responsible for casting out a particular page set or partition.

catalog

A collection of tables and views that contains descriptions of objects such as tables, views, and indexes.

catalog table

A type of table that contains information about a database or its objects, such as tables, columns, routines, privileges, or packages. Catalog tables are created and updated automatically as a result of various installation, maintenance, and usage activities.

CCS

See coded character set.

CCSID

See coded character set identifier.

CDB

See communications database.

CDRA

See Character Data Representation Architecture.

central electronic complex

See central processor complex.

central processor (CP)

The part of the computer that contains the sequencing and processing facilities for instruction execution, initial program load, and other machine operations.

central processor complex (CPC)

A physical collection of hardware that consists of main storage, one or more central processors, timers, and channels.

CF

See coupling facility.

CFRM

See coupling facility resource management.

CFRM policy

See coupling facility resource management policy.

character conversion

The process of changing data from one character coding representation to another.

Character Data Representation Architecture (CDRA)

An IBM architecture that defines a set of identifiers, resources, services, and conventions to achieve consistent representation, processing, and interchange of graphic character data in heterogeneous environments.

character large object (CLOB)

A data type whose value is a sequence of characters (single byte, multibyte, or both) that can range in size from 0 bytes to 2 gigabytes less 1 byte. In general, the CLOB data type is used whenever a character string might exceed the limits of the VARCHAR data type. See also large object.

character set

A defined set of characters with no coded representation assumed that can be recognized by a configured hardware or software system. A character set can be defined by alphabet, language, script, or any combination of these items.

character string

A sequence of bytes that represents bit data, single-byte characters, or a mixture of single-byte and multibyte characters.

check constraint

A user-defined constraint that specifies the values that specific columns of a base table can contain. See also constraint.

check integrity

The condition that exists when each row in a table conforms to the check constraints that are defined on that table.

check pending

In Db2 for z/OS, a state into which a table can be put where only limited activity is allowed on the table and constraints are not checked when the table is updated.

checkpoint

A point at which the database manager records internal status information in the log; the recovery process uses this information if the subsystem abnormally terminates.

child lock

In explicit hierarchical locking, a lock that is held on a table, a page, a row, or a large object. Each child lock has a parent lock. See also parent lock.

CI

See control interval.

CICS attachment facility

A facility that provides a multithread connection to a Db2 database to allow applications that run in the CICS environment to execute Db2 commands.

claim

A notification to Db2 for z/OS that an object is being accessed. A claim prevents a drain from occurring until the claim is released, which usually occurs at a commit point. See also drain, logical claim.

claim class

A type of object access that can be defined by one of the following characteristics: cursor stability (CS), repeatable read (RR), or write.

class of service

A VTAM term for a list of routes through a network, arranged in an order of preference for their use.

clause

In SQL, a distinct part of a statement in the language structure, such as a SELECT clause or a WHERE clause.

client

A software program or computer that requests services from a server.

CLOB

See character large object.

clone object

An object that is associated with a clone table, including the clone table itself and check constraints, indexes, and BEFORE triggers on the clone table.

clone table

A table that is structurally identical to a base table. The base and clone table each have separate underlying VSAM data sets, which are identified by their data set instance numbers. See also base table.

closed application

An application that requires exclusive use of certain statements on certain Db2 objects so that the objects are managed solely through the external interface of that application.

clustering index

An index that determines how rows are physically ordered (clustered) in a table space. If a clustering index on a partitioned table is not a partitioning index, the rows are ordered in cluster sequence within each data partition instead of spanning the partitions.

coded character set (CCS)

A set of unambiguous rules that establishes a character set and the one-to-one relationships between the characters of the set and their coded representations.

coded character set identifier (CCSID)

A 16-bit number that includes a specific set of encoding scheme identifiers, character set identifiers, code page identifiers, and other information that uniquely identifies the coded graphic-character representation. See also binary string.

code page

A particular assignment of code points to graphic characters. Within a specific code page, a code point can have only one specific meaning. A code page also identifies how undefined code points are handled. See also code point.

code point

A unique bit pattern that represents a character in a code page. See also code page.

code unit

The fundamental binary width in a computer architecture that is used for representing character data, such as 7 bits, 8 bits, 16 bits, or 32 bits. Depending on the character encoding form that is used, each code point in a coded character set (CCS) can be represented by one or more code units.

coexistence

During migration, the state during which two releases exist in the same data sharing group.

cold start

A process by which Db2 restarts without processing any log records. See also warm start.

collection

A group of packages that have the same qualifier.

column

The vertical component of a database table. A column has a name and a particular data type (for example, character, decimal, or integer).

column function

See aggregate function.

come from checking

An SNA LU 6.2 security option that defines a list of authorization identifiers that are allowed to connect to Db2 for z/OS from a partner LU.

command

A request from a terminal or automated operator for the performance of an operation or service, or for the execution of a particular program.

command prefix

A 1-character to 8-character command identifier. The command prefix distinguishes the command as belonging to an application or subsystem rather than to z/OS.

command recognition character (CRC)

A character that permits a z/OS console operator or an IMS subsystem user to route Db2 commands to specific Db2 for z/OS subsystems.

command scope

The breadth of the impact of a command in a data sharing group. In a data sharing environment, a command can have a group scope or a member scope.

commit

To end a unit of work by releasing locks so that the database changes made by that unit of work can be perceived by other processes. This operation makes the data changes permanent.

commit point

A point in time when data is considered to be consistent. See also point of consistency.

common service area (CSA)

In a z/OS operating system, a part of the common area that contains data areas that can be addressed by all address spaces but is protected during its use by the key of the requester.

communications database (CDB)

A set of tables in the Db2 for z/OS catalog that is used to establish conversations with remote database management systems.

comparison operator

In SQL, a symbol used in comparison expressions to specify a relationship between two values. Comparison operators are = (equal to), <> (not equal to), < (less than), > (greater than), <= (less than or equal to), and >= (greater than or equal to).

composite key

An ordered set of key columns of the same table.

compression dictionary

The dictionary that is referred to during the process of compression and decompression. In Db2 for z/OS, this dictionary is created from the data in a table space or table space partition. In Db2 for Linux, UNIX, and Windows, this dictionary is created from data in each table partition, data in each table in a database partition, or XML data stored in the XML storage object of a table. A compression dictionary is specific to the table space, table space partition, table, or XML storage object from which it was created.

concurrency

The shared use of resources by multiple interactive users or application processes at the same time.

conditional restart

A Db2 restart that is directed by a user-defined conditional restart control record (CRCR).

conditional restart control record (CRCR)

A queue of records in the bootstrap data set (BSDS) that is associated with a conditional restart of Db2 for z/OS. Each element in the queue indicates the choices that were made when the record was created and the progress of the restart operation it controls.

connection

In data communication, an association established between entities for conveying information. See also SQL connection.

connection context

In SQLJ, a Java object that represents a connection to a data source.

connection declaration clause

In SQLJ, a statement that declares a connection to a data source.

connection handle

The data object containing information that is associated with a connection that Db2 ODBC manages. This information includes general status information, transaction status information, and diagnostic information. See also handle, statement handle.

connection ID

See connection identifier.

connection identifier (connection ID)

A Db2 for z/OS identifier that is supplied by the attachment facility and that is associated with a specific address space connection.

consistency token

A unique identifier that is generated during precompilation, stored in the application source, and sent to the database when the package is bound. The consistency token is used to ensure the integrity of the shared application information that is stored in the database as a package.

constant

A language element that specifies an unchanging value. Constants are classified as string constants or numeric constants.

constraint

A rule that limits the values that can be inserted, deleted, or updated in a table. See also check constraint, foreign key, primary key, referential constraint, unique constraint.

context

An application's logical connection to the data source and associated Db2 ODBC connection information that allows the application to direct its operations to a data source. A Db2 ODBC context represents a Db2 thread.

contracting conversion

A process that occurs when the length of a converted string is smaller than that of the source string. See also expanding conversion.

control interval

In a key-sequenced data set or file, the set of records that an entry in the sequence-set index record points to.
A fixed-length area of direct access storage in which VSAM stores records and creates distributed free space. The control interval is the unit of information that VSAM transmits to or from direct-access storage. A control interval always includes an integral number of physical records.

conversation

A connection between two programs over a session that allows them to communicate with each other while processing a transaction. See also SQL processing conversation.

coordinator

The system component that coordinates the commit or rollback of a unit of work that includes work that is done on one or more other systems.

copy pool

A collection of names of storage groups that are processed collectively for fast replication operations.

copy target

A named set of SMS storage groups that are to be used as containers for copy pool volume copies. A copy target is an SMS construct that lets you define which storage groups are to be used as containers for volumes that are copied by using FlashCopy functions.

copy version

A point-in-time FlashCopy copy that is managed by hierarchical storage management (HSM.) Each copy pool has a version parameter that specifies the number of copy versions to be maintained on disk.

correlated column

In SQL, a relationship between the value of one column and the value of another column.

correlated reference

A reference to a column of a table or view that is outside a subquery. See also correlated subquery.

correlated subquery

A subquery that contains a correlated reference. See also correlated reference.

correlation ID

See correlation identifier.

correlation identifier (correlation ID)

In Db2 for z/OS, an identifier that is associated with a specific thread. In TSO, the correlation ID is either an authorization identifier or the job name.

correlation name

An identifier that is specified and used within a single SQL statement as the exposed name for objects such as a table, view, table function reference, nested table expression, or data change table reference. Correlation names are useful in an SQL statement to allow two distinct references to the same base table and to allow an alternative name to be used to represent an object.

cost category

A category into which Db2 for z/OS places cost estimates for SQL statements at the time the statement is bound. The cost category is externalized in the COST_CATEGORY column of the DSN_STATEMNT_TABLE when a statement is explained.

coupling facility (CF)

A special logical partition that provides high-speed caching, list processing, and locking functions in a sysplex.

coupling facility resource management (CFRM)

A component of z/OS that provides the services to manage coupling facility resources in a Parallel Sysplex. This management includes the enforcement of CFRM policies to ensure that the coupling facility and structure requirements are satisfied.

coupling facility resource management policy (CFRM policy)

The allocation rules for a coupling facility structure that are declared by a z/OS administrator.

CP

See central processor.

CPC

See central processor complex.

CRC

See command recognition character.

CRCR

See conditional restart control record.

created temporary table

A table whose definition is persistent and shared between sessions but whose data is deleted when the session in which the table was instantiated ends. The data in the table is available only within the session in which the table was instantiated. The table is defined by using the SQL statement CREATE GLOBAL TEMPORARY TABLE. See also base table, declared temporary table, temporary table.

cross-system coupling facility (XCF)

A component of z/OS that provides functions to support cooperation between authorized programs running within a sysplex.

cross-system extended services (XES)

A set of z/OS services with which multiple instances of an application or subsystem, running on different systems in a sysplex environment, can implement high-performance, high-availability data sharing by using a coupling facility.

CS

See cursor stability.

CSA

See common service area.

CT

See cursor table.

current data

Data within a host structure that is current with (that is, identical to) the data within the base table.

current SQL ID

In Db2 for z/OS, an identifier that, at a single point in time, holds the privileges that are exercised when certain dynamic SQL statements run. The current SQL ID can be a primary authorization ID or a secondary authorization ID.

current status rebuild

The second phase of restart processing during which the status of the subsystem is reconstructed from information on the log.

cursor

A named control structure used by an application program to point to and select a row of data from a set. See also cursor sensitivity, dynamic cursor, insensitive cursor, sensitive cursor, static cursor.

cursor sensitivity

The degree to which database updates made by the same application process or another application process are incorporated in the data returned by FETCH statements for a cursor after the database updates. See also cursor, insensitive cursor, sensitive cursor.

cursor stability (CS)

An isolation level under which a query in a transaction is prevented from reading any changes made to rows by statements in other transactions until the changes have been committed. A transaction using CS with an updatable cursor prevents statements in other transactions from changing and possibly reading a row until the cursor has moved from that row. See also isolation level, read stability, repeatable read, uncommitted read.

cursor table (CT)

The internal representation of a cursor.

cycle

A set of tables that can be ordered so that each table is a descendent of the one before it, and the first table is a descendent of the last table. A self-referencing table is a cycle with a single member. See also referential cycle.

D

database (DB): A collection of interrelated or independent data items that are stored together to serve one or more applications. See also database server.
database access thread (DBAT): A thread that accesses data on a local subsystem on behalf of a remote subsystem.
database administrator (DBA): A person who is responsible for the design, development, operation, maintenance, and use of a database.
database alias: The name of the target server if it is different from the location name. The database alias is used to provide the name of the database server as it is known to the network. See also alias.
database descriptor (DBD): An internal representation of a Db2 for z/OS database definition, which reflects the data definition that is in the Db2 for z/OS catalog. The objects that are defined in a database descriptor are table spaces, tables, indexes, index spaces, relationships, check constraints, and triggers. A DBD also contains information about accessing tables in the database.
database exception status: In a data sharing environment, an indication that something is wrong with a database.
database identifier (DBID): An internal identifier of the database.
database management system (DBMS): A software system that controls the creation, organization, and modification of a database and the access to the data that is stored within it.
database request module (DBRM): A data set member that is created by the Db2 for z/OS precompiler and that contains information about SQL statements. DBRMs are used in the bind process.
database server: A software program that uses a database manager to provide database services to other software programs or computers. See also database.
Data Control Language (DCL): A subset of SQL statements that is used to control access to data. GRANT, REVOKE, and TRANSFER OWNSERHIP are examples of data control language statements. See also Structured Query Language (SQL), Data Definition Language (DDL)
data currency: The state in which data that is retrieved into a host variable in a program is a copy of data in the base table.
Data Definition Language (DDL): A language for describing data and its relationships in a database. See also Structured Query Language (SQL), Data Manipulation Language (DML), Data Control Language (DCL).
data-dependent pagination: The process that is used when applications need to access part of a Db2 result set that is based on a logical key value.
data dictionary: A repository of information about an organization's application programs, databases, logical data models, users, and authorizations.
Data Manipulation Language (DML): A subset of SQL statements that is used to manipulate data. SELECT, INSERT, UPDATE, DELETE, and MERGE are examples of data manipulation language statements. See also Structured Query Language (SQL), Data Definition Language (DDL)
data partition: A VSAM data set that is contained within a partitioned table space.
data-partitioned secondary index (DPSI): A secondary index that is partitioned according to the underlying data. See also nonpartitioned secondary index.
data set: The major unit of data storage and retrieval, consisting of a collection of data in one of several prescribed arrangements and described by control information to which the system has access. See also page set.
data set instance number: A number that indicates the data set that contains the data for an object.
data sharing: The ability of subsystems or application programs to access data directly and to change it while maintaining data integrity.
data sharing group: A collection of one or more subsystems that directly access and change the same data while maintaining data integrity.
data sharing member: A Db2 subsystem that belongs to a data sharing group.
data source: A local or remote data manager. In Db2 for z/OS, a data source must be capable of supporting data access through an ODBC, or JDBC driver that supports current APIs.
data type: In SQL, a descriptor of a set of values and a set of permitted operations. A data type determines the kind of value that a column, literal, parameter, special register, or variable can have or that can be the result of an expression, a function, or a method.
data warehouse: A subject-oriented collection of data that is used to support strategic decision making. The warehouse is the central point of data integration for business intelligence. It is the source of data for data marts within an enterprise and delivers a common view of enterprise data.
DB: See database.
Db2 command: An instruction to the operating system to access and maintain the database manager. For example, Db2 commands can be used to start or stop a database and to display information about current users and the status of databases.
Db2.: See Db2 Interactive.
Db2 Interactive (Db2. ): An interactive service within Db2 for z/OS that facilitates the execution of SQL statements, Db2 operator commands, and programmer commands and the invocation of utilities.
Db2 thread: See thread.
DBA: See database administrator.
DBAT: See database access thread.
DBCLOB: See double-byte character large object.
DBCS: See double-byte character set.
DBD: See database descriptor.
DBID: See database identifier.
DBMS: See database management system.
DBRM: See database request module.
DCE: See Distributed Computing Environment.
DCLGEN: See declarations generator.
DDF: See distributed data facility.
DCL: See Data Control Language (DCL).
DDL: See Data Definition Language (DDL).
DML: See Data Manipulation Language (DML).
deadlock: Unresolved contention for the use of resources.
declarations generator (DCLGEN): A subcomponent of Db2 for z/OS that generates SQL table declarations and COBOL, C, or PL/I data structure declarations that conform to the table. The declarations are generated from Db2 system catalog information.
declared temporary table: A table that holds temporary data and is defined by using the SQL statement DECLARE GLOBAL TEMPORARY TABLE. Information about declared temporary tables is not stored in the Db2 catalog, so this kind of table is not persistent and can be used only by the application process that issued the DECLARE statement. See also base table, created temporary table, temporary table.
default subsystem name (DSN): The name of the Db2 subsystem that can connect to the control server (the default subsystem name is DSN).
default value: A predetermined value, attribute, or option that is assumed when no other value is specified. A default value can be defined for column data in Db2 tables by specifying the DEFAULT keyword in an SQL statement that changes data (such as INSERT, UPDATE, and MERGE).
deferred embedded SQL: SQL statements that are neither fully static nor fully dynamic. Like static statements, they are embedded within an application, but like dynamic statements, they are prepared during the execution of an application. See also static SQL.
deferred write: The process of asynchronously writing changed data pages to disk.
degree of parallelism: The number of concurrently executed operations that are initiated to process a query.
delete hole: A row in the result of a SELECT statement of a cursor that no longer has a corresponding row in the base table because that row was deleted. The row for the SELECT statement is no longer accessible though the cursor. See also hole, update hole.
delete rule: A rule associated with a referential constraint that either restricts the deletion of a parent row or specifies the effect of such a deletion on the dependent rows.
delete trigger: A trigger that is activated by a delete operation on the table or view that is specified in the trigger definition. See also insert trigger, instead of trigger, trigger, update trigger.
delimited identifier: A sequence of one or more characters enclosed by quotation marks ("").
delimiter token: A string constant, a delimited identifier, an operator symbol, or any of the special characters shown in syntax diagrams.
denormalization: The intentional duplication of columns in multiple tables to increase data redundancy. Denormalization is sometimes used to improve performance. See also normalization.
dependent: In SQL, an object (row, table, or table space) that has at least one parent. See also parent table space.
dependent row: A row that contains a foreign key that matches the value of a parent key in the parent row. The foreign key value represents a reference from the dependent row to the parent row. See also parent row.
dependent table: A table that is a dependent of an object. For example, a table with a foreign key is a dependent of the table containing the corresponding primary key. See also descendent table, parent table.
deprecated: Pertaining to an entity, such as a programming element or feature, that is supported but no longer recommended and that might become obsolete.
descendent: An object that is a dependent of another object or is a dependent of an object that is in turn a dependent of another object.
descendent row: A row that is a dependent of another row or is a descendent of a dependent of another row.
descendent table: A table that has a dependent relationship on a parent table or on another descendent table. See also dependent table.
deterministic function: A user-defined function with a result that is dependent on the values of the input arguments. Successive invocations with the same input values produce the same answer.
dimension: A data category that is used to organize and select monitoring context instances for reporting and analysis. Examples of dimensions are time, accounts, products, and markets.
dimension table: The representation of a dimension in a star schema. Each row in a dimension table represents all of the attributes for a particular member of the dimension. See also star join, star schema.
directory: The Db2 for z/OS system database that contains internal objects such as database descriptors and skeleton cursor tables.
disk: A storage device that includes one or more flat, circular plates with magnetic or optical surfaces on which information is stored.
distinct type: A user-defined data type that shares a common representation with a built-in data type. See also built-in data type, user-defined data type.
Distributed Computing Environment (DCE): In network computing, a set of services and tools that supports the creation, use, and maintenance of distributed applications across heterogeneous operating systems and networks.
distributed data: Data that is stored on more than one system and is available to remote users and application programs.
distributed data facility (DDF): A set of Db2 for z/OS components through which Db2 for z/OS communicates with another RDBMS.
Distributed Relational Database Architecture (DRDA): The architecture that defines formats and protocols for providing transparent access to remote data. DRDA defines two types of functions: the application requester function and the application server function.
DNS: See domain name server.
DOCID: See document ID.
document ID (DOCID): A value that uniquely identifies a row that contains an XML column. This value is stored with the row and never changes.
domain: In a database, the set of valid values for an attribute.
domain name: In Internet communications, a name of a host system. A domain name consists of a sequence of subnames that are separated by a delimiter character, for example, www.ibm.com.
domain name server (DNS): A server program that supplies name-to-address conversion by mapping domain names to IP addresses.
double-byte character large object (DBCLOB): A data type whose value is a sequence of double-byte characters that can range in size from 0 bytes to 2 gigabytes less 2 bytes. In general, the DBCLOB data type is used whenever a graphic string might exceed the limits of the VARGRAPHIC data type. See also large object.
double-byte character set (DBCS): A set of characters in which each character is represented by 2 bytes. These character sets are commonly used by national languages, such as Japanese and Chinese, that have more symbols than can be represented by a single byte. See also multibyte character set, single-byte character set.
double-precision floating-point number: A 64-bit approximate representation of a real number.
DPSI: See data-partitioned secondary index.
drain: The act of acquiring a locked resource by quiescing access to that object. See also claim.
drain lock: A lock on a claim class that prevents a claim from occurring.
DRDA: See Distributed Relational Database Architecture.
DRDA access: An open method of accessing distributed data that can be used to connect to another database server to execute packages that were previously bound at the server location.
DSN: See default subsystem name.
dynamic bind: A process by which SQL statements or XQuery expressions are bound when they are executed. See also automatic bind, static bind.
dynamic cursor: A named control structure that an application program uses to change the size of the result table and the order of its rows after the cursor is opened. See also cursor, static cursor.
dynamic dump: A dump that is issued during the execution of a program, usually under the control of that program.
dynamic IP address: A temporary IP address for a transient device or logical unit on a network: for example, a personal computer. See also IP address.

E

EA-enabled table space

A table space or index space that is enabled for extended addressability and that contains individual partitions (or pieces, for LOB table spaces) that are greater than 4 GB.

EB

See exabyte.

EBCDIC

See Extended Binary Coded Decimal Interchange Code.

element

An entity that satisfies all of the conditions of belonging to a given set. For example, an element within an array can be accessed by using the array index. See also array, ordinary array.
In markup languages, a basic unit consisting of a start tag, end tag, associated attributes and their values, and any text that is contained between the two. See also attribute.

embedded SQL

An SQL statement that is coded within an application program. See also static SQL.

enclave

In Language Environment, an independent collection of routines, one of which is designated as the main routine. An enclave is similar to a program or run unit.

encoding scheme

A set of rules to represent character data.

end column

In a system period or an application period, the column that indicates the end of the period. See also period.

entity

A person, object, or concept about which information is stored.

enumerated list

A set of Db2 objects that are defined with a LISTDEF utility control statement in which pattern-matching characters (*, %;, _, or ?) are not used.

environment

A named collection of logical and physical resources used to support the performance of a function.

environment handle

A handle that identifies the global context for database access. All data that is pertinent to all objects in the environment is associated with this handle. See also handle.

equijoin

A join whose join condition uses only the equals predicate. See also join.

error page range

A range of pages that are considered to be physically damaged.

ESC

See escape character.

escape character (ESC)

A symbol that is used to modify the interpretation of the character or characters that follow it. Examples of uses of escape characters in SQL are delimiting identifiers, delimiting character constants, and modifying the special meaning of the underscore (_) and percent (%) characters in the LIKE predicate.
A character that suppresses or selects a special meaning for one or more characters that follow.

exabyte (EB)

For processor, real and virtual storage capacities and channel volume, 2 to the power of 60 or 1 152 921 504 606 846 976 bytes. For disk storage capacity and communications volume, 1 000 000 000 000 000 000 bytes.

exception

An SQL operation that involves the EXCEPT set operator, which combines two result tables. The result of an exception operation consists of all of the rows that are in only one of the result tables.

exception table

A table that holds rows that violate referential constraints or check constraints that the CHECK DATA utility finds.

exclusive lock

A lock that prevents concurrently executing application processes from accessing database data. See also gross lock, share lock, shared lock.

executable statement

An SQL statement or XQuery expression that can be embedded in an application program, dynamically prepared and executed, or issued interactively.

execution context

In SQLJ, a Java object that can be used to control the execution of SQL statements.

exit routine

A program that receives control from another program to perform specific functions.

expanding conversion

A process that occurs when the length of a converted string is greater than that of a source string. See also contracting conversion.

explicit hierarchical locking

Locking that is used to make the parent-child relationship between resources known to the internal resource lock manager. This type of locking avoids global locking use when no inter-Db2 interest exists on a resource.

explicit privilege

A privilege that has a name and is held as the result of SQL GRANT and REVOKE statements: for example, the SELECT privilege.

exposed name

A name specified in a FROM clause such that it can be referenced elsewhere in the query. Exposed names include correlation names and, if correlation names are not specified for them, table names, view names, nicknames, and alias names.

expression

An operand or a collection of operators and operands that yields a single value.

extended addressability

The ability to create and access a Virtual Storage Access Method (VSAM) data set that is greater than 4 GB.

Extended Binary Coded Decimal Interchange Code (EBCDIC)

A coded character set of 256 8-bit characters developed for the representation of textual data. See also American Standard Code for Information Interchange.

extended recovery facility (XRF)

A facility that minimizes the effect of failures in z/OS, VTAM, the host processor, or high-availability applications during sessions between high-availability applications and designated terminals. This facility provides an alternative subsystem to take over sessions from the failing subsystem.

Extensible Markup Language (XML)

A standard metalanguage for defining markup languages that is based on Standard Generalized Markup Language (SGML).

external function

A function that has its functional logic implemented in a programming language application that is outside the database, in the file system of the database server. The association of the function with the external code application is specified by the EXTERNAL clause in the CREATE FUNCTION statement. See also external routine, function, user-defined function.

external procedure

A procedure that has its procedural logic implemented in an external programming language application. The association of the procedure with the external application is specified by a CREATE PROCEDURE statement with a LANGUAGE clause that has a value other than SQL and an EXTERNAL clause that implicitly or explicitly specifies the name of the external application. See also external routine, external SQL procedure, native SQL procedure, procedure, user-defined procedure.

external routine

A function, method, or procedure that has its routine logic implemented in a programming language application that is outside the database, in the file system of the database server. The association of the routine with the external code application is specified by the EXTERNAL clause in the CREATE statement for the routine. See also external function, external procedure, routine.

external SQL procedure

An SQL procedure that is processed using a generated C program that is a representation of the procedure. When an external SQL procedure is called, the C program representation of the procedure is executed in a stored procedures address space. See also external procedure, native SQL procedure.

F

failed member state

A state of a member of a data sharing group in which the member's task, address space, or z/OS system terminates before the state changes from active to quiesced.

fallback

The process of returning to a previous release of a software program after attempting or completing migration to a current release.

false global lock contention

A contention indication from the coupling facility that occurs when multiple lock names are hashed to the same indicator and when no real contention exists.

fan set

A direct physical access path to data, which is provided by an index, hash, or link; a fan set is the means by which Db2 supports the ordering of data.

federated database

In a federated system, the database that is within the federated server. Users and applications interface with the federated database. To these clients, the data sources and the federated database seem to be a single database.

fetch orientation

The specification of the placement of the cursor as part of a FETCH statement, for example, BEFORE or AFTER. See also scrollability.

field procedure

A user-written exit routine that receives a single value and encodes or decodes it as specified by the user.

file reference variable

A host variable that indicates that data is in a file on the client rather than in a client memory buffer.

filter factor

A number between zero and one that estimates the proportion of rows in a table for which a predicate is true.

fixed-length string

A character, graphic, or binary string whose length is specified and cannot be changed.

FlashCopy

An optional feature of the Storage System DS family that can make an instant copy of data, that is, a point-in-time copy of a volume.

foreign key

In a relational database, a key in one table that references the primary key in another table. See also constraint, primary key.
A column or set of columns that refers to a parent key.

forest

An ordered set of subtrees of XML nodes.

forward log recovery

The third phase of restart processing, during which Db2 for z/OS processes the log in a forward direction to apply all REDO log records.

free space

The total amount of unused space in a page, data set, file, storage medium, or file system. Free space is the space that is not used to store records, control information, or files.

full outer join

A join whose result consists of the matched rows of the two tables that were joined and the unmatched rows of both tables. See also join, left outer join, outer join, right outer join.

fullselect

A subselect, a values-clause, or a number of both that are combined by set operators. Fullselect specifies a result table. If UNION is not used, the result of the fullselect is the result of the specified subselect.

fully escaped mapping

A mapping of characters in an SQL identifier to characters in an XML name where some characters might be represented using XML character escapes.

function

A relationship between a set of input data values and a set of result values that is used to extend and customize SQL or XQuery. Functions are invoked from elements of SQL statements such as the select list or the FROM clause and from XQuery as primary expressions. See also aggregate function, built-in function, external function, routine, scalar function, sourced function, SQL function, table function, user-defined function.

function definer

The authorization ID of the owner of the schema of the function that is specified in the CREATE FUNCTION statement.

function package

A package that results from binding the DBRM for a function program.

function package owner

The authorization identifier of the user who binds the function program's DBRM into a function package.

function signature

The logical concatenation of a fully qualified function name with the data types of all of its parameters.

G

GB: See gigabyte.
GBP: See group buffer pool.
GBP-dependent: The status of a page set or page set partition that is dependent on the group buffer pool. Either read/write interest is active among Db2 subsystems for this page set, or the page set has changed pages in the group buffer pool that are not yet cast out to disk.
generalized trace facility (GTF): A z/OS service program that records significant system events such as I/O interrupts, SVC interrupts, program interrupts, and external interrupts.
generated column: A column for which the database manager assigns the value. An example of a generated column is an identity column, row change timestamp column, or row-begin column. See also generated expression column, row-begin column, row-end column, transaction-start-ID column.
generated expression column: A generated column that is defined using an expression. See also generated column.
generic resource name: A name used by VTAM to represent application programs that provide the same function in order to handle session distribution and balancing in a sysplex environment.
getpage: An operation in which Db2 for z/OS accesses a data page.
gigabyte (GB): For processor storage, real and virtual storage, and channel volume, two to the power of 30 or 1,073,741,824 bytes. For disk storage capacity and communications volume, 1,000,000,000 bytes.
globalization: The development of a product that is acceptable worldwide and includes internationalization and localization.
global lock: A lock that provides concurrency control within and among Db2 subsystems. The scope of the lock is across all Db2 subsystems of a data sharing group.
global lock contention: A conflict on locking requests between different members of a data sharing group when those members are trying to serialize shared resources.
governor: See resource limit facility.
graphic string: A sequence of double-byte character set (DBCS) characters.
GRECP: See group buffer pool recovery pending.
gross lock: The shared, update, or exclusive mode locks on a table, partition, or table space. See also exclusive lock, shared lock.
group buffer pool (GBP): A Db2 for z/OS coupling facility cache structure that is used by a data sharing group to cache data and to ensure that the data is consistent for all members. See also cache structure.
group buffer pool duplexing: The ability to write data to two instances of a group buffer pool structure: a primary group buffer pool and a secondary group buffer pool.
group buffer pool recovery pending (GRECP): Pertaining to the state that exists after the buffer pool for a data sharing group is lost. When a page set is in this state, changes that are recorded in the log must be applied to the affected page set before the page set can be used.
group level: The release level of a data sharing group, which is established when the first member migrates to a new release.
group name: The z/OS XCF identifier for a data sharing group.
group restart: A restart of at least one member of a data sharing group after the loss of either locks or the shared communications area.
GTF: See generalized trace facility.

H

handle: In Db2 ODBC, a variable that refers to a data structure and associated resources. See also connection handle, environment handle, statement handle.
hash access: Access to a table that uses the hash value of a key that is defined by the organization-clause of a CREATE TABLE statement or ALTER TABLE statement.
hash overflow index: A Db2 index used to track data rows that do not fit into the fixed hash space, and therefore, reside in the hash overflow space. Db2 accesses the hash overflow index to fetch rows from the hash overflow area.
heuristic damage: The inconsistency in data between one or more participants that results when a heuristic decision to resolve an indoubt LUW at one or more participants differs from the decision that is recorded at the coordinator.
heuristic decision: A decision that forces indoubt resolution at a participant by means other than automatic resynchronization between coordinator and participant.
histogram statistics: A technique for summarizing data distribution that divides the range of possible values in a data set into intervals, such that each interval contains approximately the same percentage of the values. A set of statistics are collected for each interval.
historical row: A row in a history table. See also history table.
history table: A table that is used by the database manager to store historical versions of rows from the associated system-period temporal table. See also historical row, system-period temporal table.
hole: A row of a result table that cannot be accessed because a delete operation or an update operation has been performed on that row. See also delete hole, update hole.
home address space: The area of storage that z/OS currently recognizes as dispatched.
host: In TCP/IP, any system that has at least one IP address associated with it.
host expression: A Java variable or expression that is referenced by SQL clauses in an SQLJ application program.
host identifier: A name that is declared in the host program.
host language: Any programming language in which SQL statements or XQuery expressions can be embedded.
host program: An application program that is written in a host language and that contains embedded SQL statements or XQuery expressions.
host structure: In an application program, a structure that contains a list of host variables that can be referred to by embedded SQL statements.
host variable: In an application program, a programming variable that is referred to by embedded SQL statements. The value of the host variable comes from the host program when a statement is executed or a cursor is opened. A host variable is a colon followed by a name (:name). See also parameter marker.
host variable array: An array of elements, each of which corresponds to a value for a column. The dimension of the array determines the maximum number of rows for which the array can be used.

I

IDCAMS: See access method services.
identity column: A generated column that is defined with the AS IDENTITY clause. An identity column provides a way for the database manager to automatically generate a numeric value for each row that is inserted into a table. A table can have no more than one identity column.
IFCID: See instrumentation facility component identifier.
IFI: See instrumentation facility interface.
IFI call: An invocation of the instrumentation facility interface (IFI) by means of one of its defined functions.
image copy: An exact reproduction of all or part of a table space. Db2 for z/OS provides utility programs to make full image copies (to copy the entire table space) or incremental image copies (to copy only those pages that were modified since the last image copy).
IMS attachment facility: A Db2 for z/OS subcomponent that uses z/OS subsystem interface (SSI) protocols and cross-memory linkage to process requests from IMS to Db2 for z/OS and to coordinate resource commitment.
in-abort: A status of a unit of recovery that occurs when Db2 for z/OS fails after a unit of recovery begins to be rolled back but before the process is completed. Db2 for z/OS continues to back out the changes when the process restarts. See also in-commit.
in-commit: A status of a unit of recovery that occurs when Db2 for z/OS fails after beginning its two-phase commit processing. When Db2 for z/OS is restarted, this status indicates that changes made to data are consistent. See also in-abort.
independent: Pertaining to an object (row, table, or table space) that is neither a parent nor a dependent of another object.
index: A set of pointers that is logically ordered by the values of a key. Indexes provide quick access to data and can enforce uniqueness of the key values for the rows in the table.
index-controlled partitioning: A type of partitioning in which partition boundaries for a partitioned table are controlled by values that are specified on the CREATE INDEX statement. Partition limits are saved in the LIMITKEY column of the SYSIBM.SYSINDEXPART catalog table.
index key: The set of columns in a table that is used to determine the order of index entries.
index partition: A VSAM data set that is contained within a partitioning index space.
index space: One or more page sets that stores the entries of an index. See also page set, partition.
indicator column: A 4-byte value that is stored in a base table in place of an LOB column.
indicator variable: A variable that is used with a host variable to represent the SQL null value in an application program.
indoubt: The status of a unit of recovery that occurs when the database manager fails after it finishes its phase 1 commit processing and before it starts phase 2. At emergency restart, the status of the unit of recovery is indoubt until the commit coordinator indicates to the database manager whether the unit of recovery is to be committed or rolled back.
indoubt resolution: The process of resolving the status of an indoubt logical unit of work to either the committed or the rollback state.
inflight: The state of a resource or unit of recovery that has not yet completed the prepare phase of the commit process.
inheritance: An object-oriented programming technique in which existing classes are used as a basis for creating other classes. Through inheritance, more specific elements incorporate the structure and behavior of more general elements.
initialization file: For Db2 ODBC applications, a file containing values that can be set to adjust the performance of the database manager.
inline copy: A copy that is produced by the LOAD or REORG utility. The data set that the inline copy produces is logically equivalent to a full image copy that is produced by running the COPY utility with read-only access.
inline SQL PL: A subset of SQL procedural language that can be used in SQL functions, triggers, and dynamic compound statements.
inner join: The result of a join operation that includes only the matched rows of both tables that are being joined. See also join, outer join.
inoperative package: A package that is not usable because one or more user-defined functions, procedures, or methods on which the package depends were dropped. See also invalid package.
insensitive cursor: A cursor that is not sensitive to inserts, updates, or deletes that are made to the underlying rows of a result table after the result table has been materialized. See also cursor, cursor sensitivity.
insert trigger: A trigger that is activated by an insert operation on the table or view that is specified in the trigger definition. See also delete trigger, instead of trigger, trigger, update trigger.
installation: The process of preparing a Db2 subsystem to operate as a z/OS subsystem.
instead of trigger: A trigger that is associated with a single view and is activated by an insert, update, or delete operation on the view and that defines how to propagate the insert, update, or delete operation on the view to the underlying tables of the view. See also after trigger, before trigger, delete trigger, insert trigger, trigger, update trigger.
instrumentation facility component identifier (IFCID): In Db2 for z/OS, a value that names and identifies a trace record of an event. As a parameter on the START TRACE and MODIFY TRACE commands, it specifies that the corresponding event is to be traced.
instrumentation facility interface (IFI): A programming interface that enables programs to obtain online trace data about Db2, to submit Db2 commands, and to pass data to Db2 .
Interactive System Productivity Facility (ISPF): An IBM licensed program that serves as a full-screen editor and dialog manager. Used for writing application programs, it provides a means of generating standard screen panels and interactive dialogs between the application programmer and the terminal user. See also Time Sharing Option.
inter-Db2 R/W interest: A property of data in a table space, an index, or a partition that has been opened by more than one member of a data sharing group for writing by at least one of those members.
intermediate database server: The target of a request from a local application or a remote application requester that is forwarded to another database server.
internal resource lock manager (IRLM): A global lock manager that resides in its own address space and provides the option of keeping most of its control blocks in local storage rather than the common storage area.
intersection: An SQL operation that involves the INTERSECT set operator, which combines two result tables. The result of an intersection operation consists of all of the rows that are in both result tables.
invalid package: In Db2 Version 9.1 for z/OS and earlier, a package that depends on an object (other than a user-defined function) that is dropped. Such a package is implicitly rebound on invocation. See also inoperative package.
IP address: A unique address for a device or logical unit on a network that uses the Internet Protocol standard. See also dynamic IP address, static IP address.
IRLM: See internal resource lock manager.
isolation level: An attribute that defines the degree to which an application process is isolated from other concurrently executing application processes. Isolation levels generally relate to the behavior of an application with respect to locks. See also cursor stability, read stability, repeatable read, uncommitted read.
ISPF: See Interactive System Productivity Facility.
iterator: In SQLJ, an object that contains the result set of a query. An iterator is equivalent to a cursor in other host languages.
iterator declaration clause: In SQLJ, a statement that generates an iterator declaration class. An iterator is an object of an iterator declaration class.

J

JAR: See Java archive.
Java archive (JAR): A compressed file format for storing all of the resources that are required to install and run a Java program in a single file.
Java Database Connectivity (JDBC): An industry standard for database-independent connectivity between the Java platform and a wide range of databases. The JDBC interface provides a call level interface for SQL-based and XQuery-based database access. See also Open Database Connectivity.
JCL: See job control language.
JDBC: See Java Database Connectivity.
JES: See Job Entry Subsystem.
job control language (JCL): A command language that identifies a job to an operating system and describes the job requirements.
Job Entry Subsystem (JES): An IBM licensed program that receives jobs into the system and processes all output data that is produced by those jobs.
join: An SQL relational operation in which data can be retrieved from two tables, typically based on a join condition specifying join columns. See also equijoin, full outer join, inner join, left outer join, outer join, right outer join, star join.

K

KB: See kilobyte.
Kerberos: A network authentication protocol that is based on symmetric key cryptography. Kerberos assigns a unique key, called a ticket, to each user who logs on to the network. The ticket is embedded in messages that are sent over the network. The receiver of a message uses the ticket to authenticate the sender.
Kerberos ticket: A transparent application mechanism that transmits the identity of an initiating principal to its target. A simple ticket contains the identity of the principal, a session key, a timestamp, and other information, which are sealed using the secret key of the target.
key: A column or an ordered collection of columns that is identified in the description of a table, index, or referential constraint. The same column can be part of more than one key.
key-sequenced data set (KSDS): A VSAM file or data set whose records are loaded in key sequence and controlled by an index.
keyword: One of the predefined words of a programming language, artificial language, application, or command.
kilobyte (KB): For processor storage, real and virtual storage, and channel volume, 2 to the power of 10 or 1,024 bytes. For disk storage capacity and communications volume, 1,000 bytes.
KSDS: See key-sequenced data set.

L

large object (LOB): A sequence of bytes with a size ranging from 0 bytes to 2 gigabytes less 1 byte. There are three types of LOBs: binary large objects (binary), character large objects (single-byte character or mixed), and double-byte character large objects (double-byte character). See also binary large object, character large object, double-byte character large object.
last agent optimization: An optimized commit flow for either presumed-nothing or presumed-abort protocols in which the last agent, or final participant, becomes the commit coordinator. This flow saves at least one message.
latch: An internal mechanism for controlling concurrent events or the use of system resources.
LCID: See log control interval definition.
LDS: See linear data set.
leaf page: A page that contains pairs of keys and record identifiers and that points to actual data. See also nonleaf page.
left outer join: A join whose result consists of the matched rows of the two tables that were joined and the unmatched rows of the first table. See also full outer join, join, outer join, right outer join.
limit key: The highest value of the index key for a partition.
linear data set (LDS): A VSAM data set that contains data but no control information. An LDS can be accessed as a byte-addressable string in virtual storage.
linkage editor: A computer program for creating load modules from one or more object modules or load modules by resolving cross-references among the modules and, if necessary, adjusting addresses.
link-edit: To create a loadable computer program by using a linkage editor.
list: A type of object, which Db2 utilities can process, that identifies multiple table spaces, multiple index spaces, or both. A list is defined with the LISTDEF utility control statement.
list structure: A coupling facility structure that lets data be shared and manipulated as elements of a queue.
L-lock: See logical lock.
load module: A program in a form suitable for loading into main storage for execution.
LOB: See large object.
LOB locator: A mechanism that allows an application program to manipulate a large object (LOB) value in the database system. An LOB locator is a simple token value that represents a single LOB value. An application program retrieves a LOB locator into a host variable and can then apply SQL operations to the associated LOB value using the locator.
LOB lock: A lock on an LOB value.
LOB table space: In Db2 for z/OS, a table space that contains all of the data for a particular LOB column in the related base table.
local: Pertaining to a device, file, or system that is accessed directly from a user system, without the use of a communication line. See also remote.
locale: A setting that identifies language or geography and determines formatting conventions such as collation, case conversion, character classification, the language of messages, date and time representation, and numeric representation.
local lock: A lock that provides intra-Db2 concurrency control, but not inter-Db2 concurrency control; its scope is a single Db2 .
local subsystem: The unique relational database management system to which a user or an application program is directly connected. In the case of Db2 for z/OS, the connection is established by means of an attachment facility.
location: A specific relational database server in a distributed relational database system. Each location has a unique location name.
location alias: An alternative name used by the database server to identify itself in the network. Applications can use the location alias to access a Db2 database server.
location name: The unique name of a database server. An application uses the location name to access a Db2 database server. See also LU name.
lock: A means of serializing a sequence of events or serializing access to data.
lock duration: The interval over which a Db2 lock is held.
lock escalation: The response that occurs when the number of locks issued for one agent exceeds the limit specified in the database configuration; the limit is defined by the maxlocks configuration parameter. During a lock escalation, locks are freed by converting multiple locks on rows of a table into one lock on a table. This process is repeated until the limit is no longer exceeded.
locking: A process that ensures the integrity of data. Locking prevents concurrent users from accessing inconsistent data.
lock mode: A representation for the type of access that concurrently running programs can have to a resource that a lock is holding.
lock object: The resource that is controlled by a lock.
lock promotion: The process of changing the size or mode of a lock to a higher, more restrictive level.
lock size: The amount of data that is controlled by a lock on table data. Examples of lock size values are table, row, and page.
lock structure: A coupling facility data structure that is composed of a series of lock entries to support shared and exclusive locking for logical resources.
log: A collection of records that sequentially describes the events that occur in a system.
log control interval definition (LCID): A suffix of the physical log record that tells how record segments are placed in the physical control interval.
logical claim: A claim on a logical partition of a nonpartitioning index. See also claim.
logical index partition: The set of all keys that reference the same data partition.
logical lock (L-lock): The lock type that transactions use to control intra-Db2 and inter-Db2 data concurrency between transactions. See also physical lock.
logically complete: A state in which the concurrent copy process is finished with the initialization of the target objects that are being copied. The target objects are available for update.
logical page list (LPL): A list of pages that are in error and that cannot be referenced by applications until the pages are recovered. These pages are in logical error even though the actual media (coupling facility or DASD) might not contain any errors. Usually, a connection to the media has been lost.
logical partition (LP, LPAR): A set of key or RID pairs in a nonpartitioning index that is associated with a particular partition.
logical recovery pending (LRECP): The state in which data and the index keys that refer to that data are inconsistent.
logical unit (LU): An access point through which a user or application program accesses the SNA network to communicate with another user or application program.
logical unit of work (LUW): The processing that a program performs between synchronization points.
logical unit of work identifier (LUWID): A name that uniquely identifies a thread within a network. This name consists of a fully qualified logical unit network name, a logical unit of work instance number, and a logical unit of work sequence number.
log initialization: The first phase of restart processing during which the current end of the log is located.
log record header (LRH): A prefix, in every log record, that contains control information.
log record sequence number (LRSN): A unique identifier for a log record that is associated with a data sharing member. Db2 for z/OS uses the LRSN for recovery in the data sharing environment.
log truncation: A process by which an explicit starting relative byte address (RBA) is established. This RBA is the point at which the next byte of log data is to be written.
LP: See logical partition.
LPAR: See logical partition.
LPL: See logical page list.
LRECP: See logical recovery pending.
LRH: See log record header.
LRSN: See log record sequence number.
LU: See logical unit.
LU name: The name by which VTAM refers to a node in a network. See also location name.
LUW: See logical unit of work.
LUWID: See logical unit of work identifier.

M

mapping table

A table that the REORG utility uses to map the associations of the RIDs of data records in the original copy and in the shadow copy. This table is created by the user.

mass delete

The deletion of all rows of a table.

materialize

To put rows from a view or nested table expression into a work file for additional processing by a query.
To place an LOB value into contiguous storage. Because LOB values can be very large, Db2 for z/OS avoids materializing LOB data until doing so becomes absolutely necessary.

materialized query table (MQT)

A base table whose definition is based on the result of a query and whose data is in the form of precomputed results that are taken from the table or tables on which the MQT definition is based.

MB

See megabyte.

MBCS

See multibyte character set.

megabyte (MB)

For processor storage, real and virtual storage, and channel volume, 2 to the 20th power or 1,048,576 bytes. For disk storage capacity and communications volume, 1,000,000 bytes.

member name

The z/OS XCF identifier for a particular Db2 for z/OS subsystem in a data sharing group.

metalanguage

A language that is used to create other specialized languages.

migrate

To install a new version or release of a program to replace an earlier version or release.

mixed data string

A character string that contains both single-byte and double-byte characters.

mode name

A name for the collection of physical and logical characteristics and attributes of a session.

modify lock

An L-lock or a P-lock with a MODIFY attribute. A list of these active locks is kept at all times in the coupling facility lock structure. If the requesting subsystem fails, that subsystem's modify locks are converted to retained locks.

MQT

See materialized query table.

multibyte character set (MBCS)

A character set that represents single characters with more than a single byte. See also double-byte character set, single-byte character set, Unicode.

multidimensional analysis

The process of assessing and evaluating an enterprise on more than one level. See also business dimension.

Multiple Virtual Storage (MVS)

An IBM operating system that accesses multiple address spaces in virtual storage.

multisite update

Distributed relational database processing in which data is updated in more than one location within a single unit of work. See also unit of work.

multithreading

A mode of operation in which the operating system can run different parts of a program, called threads, simultaneously.

MVS

See Multiple Virtual Storage.

N

native SQL procedure: An SQL procedure that is processed by converting the procedural statements to a native representation that is stored in the database directory, as is done with other SQL statements. When a native SQL procedure is called, the native representation is loaded from the directory, and Db2 executes the procedure. See also external procedure, external SQL procedure.
nested table expression: A fullselect surrounded by parentheses in a FROM clause.
network identifier (NID): The network ID that is assigned by IMS or CICS, or if the connection type is RRSAF, the RRS unit of recovery ID (URID).
NID: See network identifier.
node ID index: See XML node ID index.
non-deterministic function: A user-defined function whose result is not solely dependent on the values of the input arguments. That is, successive invocation with the same argument value can produce a different answer.
nonleaf page: An index page that contains keys and page numbers of other pages in the index (either leaf or nonleaf pages). Nonleaf pages never point to actual data. See also leaf page.
nonpartitioned index: An index that is not physically partitioned. Both partitioning indexes and secondary indexes can be nonpartitioned. See also secondary index.
nonpartitioned secondary index (NPSI): An index on a partitioned table space that is not the partitioning index and is not partitioned. See also data-partitioned secondary index.
nonscrollable cursor: A cursor that can be moved only in a forward direction. Nonscrollable cursors are sometimes called forward-only cursors or serial cursors. See also scrollable cursor.
normalization: The process of restructuring a data model by reducing its relations to their simplest forms. It is a key step in the task of building a logical relational database design. Normalization helps avoid redundancies and inconsistencies in data. An entity is normalized if it meets a set of constraints for a particular normal form (first normal form, second normal form, and so on). See also denormalization, repeating group.
not-variant function: See deterministic function.
NPSI: See nonpartitioned secondary index.
null terminator: In C, the value that indicates the end of a string. For EBCDIC, ASCII, and Unicode UTF-8 strings, the null terminator is a single-byte value (X'00'). For Unicode UTF-16 and UCS-2 (wide) strings, the null terminator is a double-byte value (X'0000').

O

ODBC: See Open Database Connectivity.
ODBC driver: A dynamically linked library (DLL) that implements ODBC function calls and interacts with a data source.
offset: The number of rows to skip from the beginning of a result table. The offset of the beginning row is 0 (not 1).
OLAP: See online analytical processing.
online analytical processing (OLAP): The process of collecting data from one or many sources; transforming and analyzing the consolidated data quickly and interactively; and examining the results across different dimensions of the data by looking for patterns, trends, and exceptions within complex relationships of that data.
Open Database Connectivity (ODBC): A standard application programming interface (API) for accessing data in both relational and nonrelational database management systems. Using this API, database applications can access data stored in database management systems on a variety of computers even if each database management system uses a different data storage format and programming interface. See also Java Database Connectivity.
ordinary array: An array with a defined upper boundary on the number of elements, which are referenced by their ordinal position in the array. See also array, associative array, element.
ordinary identifier: An uppercase letter followed by zero or more characters, each of which is an uppercase letter, a number, or the underscore character. An ordinary identifier should not be a reserved word.
ordinary token: A numeric constant, an ordinary identifier, a host identifier, or a keyword.
originating task: The primary agent in a parallel group that receives data from other execution units (referred to as parallel tasks) that are executing portions of the query in parallel. See also parallel task.
outer join: A join whose result consists of the matched rows of the two tables that were joined and the unmatched rows of one or both tables. See also full outer join, inner join, join, left outer join, right outer join.
overloaded function: A function name for which multiple function instances exist.

P

package: A control-structure database object produced during program preparation that can contain both executable forms of static SQL statements or XQuery expressions and placement holders for executable forms of dynamic SQL statements.
package list: An ordered list of package names that can be used to extend an application plan.
package name: The name of an object that is created by the BIND, PRECOMPILE, or REBIND command. The object is a bound version of a database request module (DBRM). The name consists of a location name, a collection ID, a package ID, and a version ID.
page: In Db2 for Linux, UNIX, and Windows and Db2 for z/OS, a unit of storage within a table space, an index space, or virtual memory. In a table space, a page can contain one or more rows of a table. In an LOB table space, an LOB value can span more than one page, but no more than one LOB value is stored on a page.
page set: A collection of VSAM data sets for a partition, table space, or index space. See also data set, index space, partition, table space.
page set recovery pending (PSRCP): A restrictive state of an index space in which the entire page set must be recovered. Recovery of a logical part is prohibited.
panel: A formatted display of information on a screen that can also include entry fields.
parallel complex: A cluster of machines that work together to handle multiple transactions and applications.
parallel group: A set of consecutive operations that execute in parallel and that have the same number of parallel tasks.
parallel I/O processing: A form of I/O processing in which Db2 for z/OS initiates multiple concurrent requests for a single user query and performs I/O processing concurrently (in parallel) on multiple data partitions.
parallelism assistant: In sysplex query parallelism, a Db2 subsystem that helps to process parts of a parallel query that originates on another Db2 subsystem in the data sharing group.
parallelism coordinator: In sysplex query parallelism, the Db2 subsystem from which the parallel query originates.
Parallel Sysplex: A set of z/OS systems that communicate and cooperate with each other through multisystem hardware components and software services to process customer workloads.
parallel task: The execution unit that is dynamically created to process a query in parallel. A parallel task is implemented by a z/OS service request block. See also originating task.
parameter marker: In the statement string of a dynamic SQL statement, a placeholder that represents a value that will be provided by the application program. The value of a parameter marker is provided on the EXECUTE or OPEN statement associated with the dynamic SQL statement. A parameter marker can be used where a host variable might be used if the statement string were a static SQL statement. A parameter marker is either a question mark (?) or a colon followed by a name (:name). See also host variable, typed parameter marker, untyped parameter marker.
parameter name: An identifier that names a parameter that can be referenced in a procedure or user-defined function.
parent key: A primary key or unique key that is used in a referential constraint. The values of a parent key determine the valid values of the foreign key in the constraint.
parent lock: For explicit hierarchical locking, a lock that is held on a resource that might have child locks that are lower in the hierarchy. A parent lock is usually the table space lock or the partition intent lock. See also child lock.
parent row: A row that has at least one dependent row. See also dependent row.
parent table: A table that is a parent in at least one referential constraint. See also dependent table.
parent table space: A table space that contains a parent table. A table space containing a dependent of that table is a dependent table space. See also dependent.
participant: An entity other than the commit initiator that takes part in the commit process.
partition: A page set that corresponds to a single data set that can be processed or extended independently. See also index space, page set, partitioned table space, universal table space.
partition-by-growth table space: A table space that has partitions based on data growth, and segmented organization. See also partition-by-range table space, partitioned table space, universal table space.
partition-by-range table space: A table space that has partitions based on data value ranges, and segmented organization. See also partition-by-growth table space, partitioned table space, range-partitioned table space.
partitioned data set (PDS): A data set on direct access storage that is divided into partitions, called members, each of which can contain a program, part of a program, or data. See also sequential data set.
partitioned index: An index that is physically partitioned. Both partitioning indexes and secondary indexes can be partitioned.
partitioned page set: A partitioned table space or an index space. Header pages, space map pages, data pages, and index pages reference data only within the scope of the partition.
partitioned table space: A table space that is divided into partitions. See also partition, partition-by-growth table space, partition-by-range table space, range-partitioned table space, universal table space.
partitioning index: An index in which the leftmost columns are the partitioning columns of the table. The index can be partitioned or nonpartitioned.
partner logical unit (partner LU): In SNA, the remote participant in a session.
partner LU: See partner logical unit.
PDS: See partitioned data set.
period: In a table, an interval of time that is defined by two datetime columns. A period contains a begin column and an end column. See also begin column, end column.
phase-in rebind: An operation in which the REBIND PACKAGE command might create a new current copy of the package and the existing current copy is retained as a phase-out copy. Although multiple copies of an existing package can exist, only one copy can ever be the current copy. At any point in time, there can be one original copy, one previous copy, and multiple phased-out copies. See also autobind phase-in.
physical consistency: The state of a page that is not in a partially changed state.
physical lock (P-lock): A type of lock that Db2 acquires to provide consistency of data that is cached in different Db2 subsystems. Physical locks are used only in data sharing environments. See also logical lock.
physically complete: The state in which the concurrent copy process is completed and the output data set has been created.
piece: A data set of a nonpartitioned page set.
plan allocation: The process of allocating Db2 for z/OS resources to a plan in preparation to execute it.
plan member: The bound copy of a database request module (DBRM) that is identified in the member clause.
plan name: The name of an application plan.
P-lock: See physical lock.
point of consistency: A time when all of the recoverable data that a program accesses is consistent. The point of consistency occurs when updates, insertions, and deletions are either committed to a physical database or rolled back. See also commit point, roll back.
postponed abort UR: A unit of recovery that was inflight or in-abort, was interrupted by system failure or cancellation, and did not complete backout during restart.
precision: An attribute of a number that describes the total number of binary or decimal digits.
precompile: To process programs that contain SQL statements before they are compiled. SQL statements are replaced with statements that will be recognized by the host language compiler. The output from a precompile process includes source code that can be submitted to the compiler and used in the bind process.
predicate: An element of a search condition that expresses or implies a comparison operation.
prefix: A code at the beginning of a message or record.
preformat: To prepare a VSAM linear data set for Db2 use, by writing specific data patterns.
prepare: To convert an SQL statement from text form to an executable form. See also program preparation.
prepared SQL statement: A named object that is the executable form of an SQL statement that was processed by the PREPARE statement.
prepare phase: The first phase of a two-phase commit process in which all participants are requested to prepare for commit.
primary authorization ID: The authorization identifier used to identify an application process to Db2 for z/OS. See also secondary authorization ID.
primary group buffer pool: For a duplexed group buffer pool, the structure that is used to maintain the coherency of cached data. This structure is used for page registration and cross-invalidation. The z/OS equivalent is old structure. See also secondary group buffer pool.
primary index: An index that enforces the uniqueness of a primary key.
primary key: In a relational database, a key that uniquely identifies one row of a database table. See also constraint, foreign key.
principal: An entity that can communicate securely with another entity. A principal is identified by its associated security context, which defines its access rights.
principal name: The name by which a principal is known to the Distributed Computing Environment (DCE) security services.
privilege: The capability of performing a specific function, sometimes on a specific object.
privilege set: For the predefined SYSADM ID, the set of all possible privileges. For any other authorization identifier, the set of all privileges that are recorded for that identifier in the Db2 for z/OS catalog.
procedure: A routine that can be invoked using the SQL CALL statement to perform operations that can include both host language statements and SQL statements. See also external procedure, routine, SQL procedure, user-defined procedure.
process: An instance of a program running on a system and the resources that it uses.
program: A single, compilable collection of executable statements in a programming language.
program preparation: The process of producing a program. The process includes precompilation, compilation, and bind. See also prepare.
program temporary fix (PTF): For IBM i, System p, and IBM® zSystems products, a package containing individual or multiple fixes that is made available to all licensed customers. A PTF resolves defects and might provide enhancements.
protected conversation: A conversation that supports the two-phase commit process for the synchronization of changes.
PSRCP: See page set recovery pending.
PTF: See program temporary fix.
public alias: An alias defined in the SYSPUBLIC schema that can always be referenced by its unqualified name without any impact from the current default schema name. See also alias.

Q

QSAM: See queued sequential access method.
query: A component of certain SQL or XQuery statements that specifies a result set.
query block: The part of a query that is represented by one of the FROM clauses. Each FROM clause can have multiple query blocks, depending on how Db2 for z/OS processes the query.
query CP parallelism: Parallel execution of a single query, which is accomplished by using multiple tasks. See also sysplex query parallelism.
query I/O parallelism: Parallel access of data, which is accomplished by triggering multiple I/O requests within a single query.
queued sequential access method (QSAM): An access method for storing and retrieving logical records in a continuous sequence. Input data blocks awaiting processing or output data blocks awaiting transfer to auxiliary storage are queued on the system to minimize delays in I/O operations.
quiesce point: A point at which data is consistent as a result of running the Db2 QUIESCE utility.

R

RACF

See Resource Access Control Facility.

range-partitioned table space

A table space that has partitions based on data value ranges. See also partition-by-range table space, partitioned table space, universal table space.

RBA

See relative byte address.

RCT

See resource control table.

RDB

See relational database.

RDBMS

See relational database management system.

RDMS

See relational database management system.

RDO

See resource definition online.

read stability (RS)

An isolation level under which a query that is issued more than once in a transaction is guaranteed to read the same rows for each subsequent execution. However, in subsequent executions, the query might read additional (phantom) rows that were inserted or updated and then committed by statements in concurrently running transactions. A query in a transaction using RS is prevented from reading any rows changed by statements in other transactions until the changes have been committed. Also, until the transaction using RS has been committed, any rows that a query in that transaction reads cannot be changed by statements in other transactions. See also cursor stability, isolation level, repeatable read, uncommitted read.

rebind

To create a package for an application program by using information from the previously bound package. For example, in Db2 for Linux, UNIX, and Windows and Db2 for z/OS, if an index is added for a table that is accessed by a program, the package must be rebound for it to take advantage of the new index.

rebuild

To restore a database or a subset of its table spaces by using a set of table space restore operations.

record

The storage representation of a row or other data. See also row.

record identifier (RID)

A unique identifier that the Db2 database manager uses internally to identify a row of data in a table.

record identifier pool (RID pool)

An area of main storage that is used for sorting record identifiers during list-prefetch processing.

record length

The total length of all the columns in a table. The record length is the length of the data as physically stored in the database. Records can be fixed or variable in length, depending on how the columns are defined. If all columns are fixed-length columns, the record is a fixed-length record. If one or more columns are varying-length columns, the record is a varying-length record.

Recoverable Resource Manager Services attachment facility

A Db2 subcomponent that uses Resource Recovery Services to coordinate resource commitments between Db2 and all other resource managers that also use RRS in a z/OS system.

recovery

The process of re-creating a database or table space that became unusable because of hardware failure, software failure, or both. The process includes restoring a backup image and can also include rolling database logs forward in time.

recovery log

A collection of records that describes the events that occur during Db2 execution and indicates their sequence. The recorded information is used for recovery in the event of a failure during Db2 execution.

recovery manager

A subcomponent that supplies coordination services that control the interaction of Db2 resource managers during commit, abort, checkpoint, and restart processes. The recovery manager also supports the recovery mechanisms of other subsystems (for example, IMS) by acting as a participant in the other subsystem's process for protecting data that has reached a point of consistency.
A coordinator or a participant (or both), in the execution of a two-phase commit, that can access a recovery log that maintains the state of the logical unit of work and names the immediate upstream coordinator and downstream participants.

recovery pending (RECP)

The state of a database or table space when it is restored from a backup. While the database or table space is in this state, its data cannot be accessed.

recovery token

An identifier for an element that is used in recovery (for example, NID or URID).

RECP

See recovery pending.

redo

A state of a unit of recovery that indicates that changes are to be reapplied to the disk media to ensure data integrity.

reentrant code

Executable code that can reside in storage as one shared copy for all threads. Reentrant code is not self-modifying and provides separate storage areas for each thread. See also threadsafe.

referential constraint

The requirement that the nonnull values of a designated foreign key are valid only if they are also values of the primary key of the parent table. The referential constraint is always defined from the perspective of the dependent file. See also constraint.

referential cycle

A set of referential constraints such that each table in the set is a descendent of itself. See also cycle.

referential integrity

The state of a database in which all values of all foreign keys are valid. Maintaining referential integrity requires the enforcement of a referential constraint on all operations that change the data in a table where the referential constraints are defined.

referential structure

A set of tables and relationships such that for every table in the set, the set includes all relationships in which that table participates and all the tables to which it is related.

refresh age

The time duration between the current time and the time during which a materialized query table was last refreshed.

registry database

In a z/OS environment, a database of security information about principals, groups, organizations, accounts, and security policies.

relational database (RDB)

A database that can be perceived as a set of tables and manipulated in accordance with the relational model of data. Each database includes a set of system catalog tables that describe the logical and physical structure of the data, a configuration file containing the parameter values allocated for the database, and a recovery log with ongoing transactions and archivable transactions.

relational database management system (RDBMS, RDMS)

A collection of hardware and software that organizes and provides access to a relational database.

relational schema

See SQL schema.

relationship

A defined connection between the rows of a table or the rows of two tables. A relationship is the internal representation of a referential constraint.

relative byte address (RBA)

The offset of a data record or control interval from the beginning of the storage space that is allocated to the data set or file to which it belongs.

remigration

The process of returning to a current release of a Db2 database system following a fallback to a previous release. This procedure constitutes another migration.

remote

Any object that is maintained by a remote Db2 subsystem (that is, by a Db2 subsystem other than the local one). A remote view, for example, is a view that is maintained by a remote Db2 subsystem. See also local.

remote subsystem

Any relational database management system (RDBMS), except the local subsystem, with which the user or application can communicate. The subsystem need not be remote in any physical sense and might even operate on the same processor under the same z/OS system.

reoptimization

The process of reconsidering, at run time, the access path of an SQL statement that has already been optimized. During reoptimization, the actual values of host variables, parameter markers, and special registers might be considered in choosing the access path.

reordered row format

A row format that facilitates improved performance in retrieval of rows that have varying-length columns. Db2 rearranges the column order, as defined in the CREATE TABLE statement, so that the fixed-length columns are stored at the beginning of the row and the varying-length columns are stored at the end of the row. See also basic row format.

REORG pending (REORP)

A condition that restricts SQL access and most utility access to an object that must be reorganized.

REORP

See REORG pending.

repeatable read (RR)

An isolation level under which a query that is issued more than once in a transaction reads the same rows again for each subsequent execution, except for rows that might have been changed earlier in the same transaction. Additional (phantom) rows are not read. A query in a transaction using RR is prevented from reading any rows changed by statements in other transactions until the changes have been committed. Also, until the transaction using RR has been committed, any rows that a query in that transaction reads cannot be changed by statements in other transactions. See also cursor stability, isolation level, read stability, uncommitted read.

repeating group

An entity that includes multiple attributes that are inherently the same. The presence of a repeating group violates the requirement of first normal form. In an entity that satisfies the requirement of first normal form, each attribute is independent and unique in its meaning and its name. See also normalization.

replay detection mechanism

A method that allows a principal to detect whether a request is a valid request from a source that can be trusted or whether an untrustworthy entity has captured information from a previous exchange and is replaying the information exchange to gain access to the principal.

request commit

The vote that is submitted to the prepare phase if the participant has modified data and is prepared to commit or roll back.

requester

The source of a request to access data at a remote server.

resource

The object of a lock or claim, which can be a table space, an index space, a data partition, an index partition, or a logical partition.

Resource Access Control Facility (RACF)

An IBM licensed program that provides access control by identifying users to the system; verifying users of the system; authorizing access to protected resources; logging unauthorized attempts to enter the system; and logging accesses to protected resources.

resource allocation

The part of plan allocation that deals specifically with database resources.

resource control table (RCT)

A Db2 control table that defines the relationship between CICS transactions and Db2 resources.

resource definition online (RDO)

A method for defining CICS resources interactively while CICS is running.

resource limit facility (RLF)

A portion of Db2 code that prevents dynamic manipulative SQL statements from exceeding specified time limits. The resource limit facility is sometimes called the governor.

resource limit specification table

A site-defined table that specifies the limits to be enforced by the resource limit facility.

resource manager

A participant, in the execution of a one-phase or two-phase commit, that has recoverable resources that could have been modified. The resource manager has access to a recovery log so that it can commit or roll back the effects of the logical unit of work to the recoverable resources.
A function that is responsible for managing a particular resource and that guarantees the consistency of all updates made to recoverable resources within a logical unit of work. The resource that is being managed can be physical (for example, disk or main storage) or logical (for example, a particular type of system service).

Resource Recovery Services attachment facility (RRSAF)

A Db2 subcomponent that uses Resource Recovery Services to coordinate resource commitment between Db2 and all other resource managers that also use RRS in a z/OS system. See also call attachment facility.

restart pending (RESTP)

A restrictive state of a page set or partition that indicates that restart (backout) work must be performed on the object.

RESTP

See restart pending.

result set

A set of row values as returned by, for example, a cursor or procedure. See also result table.

result set locator

A value used by a Db2 application to uniquely identify a query result set returned by a procedure.

result table

The set of rows produced by the evaluation of a SELECT statement. See also base table, result set, temporary table.

retained lock

A MODIFY lock that a Db2 subsystem was holding at the time of a subsystem failure. The lock is retained in the coupling facility lock structure across a Db2 for z/OS failure.

RID

See record identifier.

RID pool

See record identifier pool.

right outer join

A join whose result consists of the matched rows of the two tables that were joined and the unmatched rows of the second table. See also full outer join, join, left outer join, outer join.

RLF

See resource limit facility.

role

A database entity that groups together one or more privileges and that can be assigned, for example, to users, PUBLIC, other roles, or trusted contexts.

rollback

The process of restoring data that was changed by SQL statements to the state at its last commit point. All locks are freed.

roll back

To restore data that is changed by an SQL statement to the state at its last commit point. See also backout, point of consistency.

root page

The index page that is at the highest level (or the beginning point) in an index.

routine

A database object that can encapsulate procedural logic and SQL statements, is stored on a database server, and can be invoked using an SQL statement such as the CALL statement. The three main classes of routines are procedures, functions, and methods. See also aggregate function, built-in function, external routine, function, procedure, scalar function, sourced function, SQL function, SQL procedure, SQL routine, table function, user-defined function, user-defined procedure.

row

The horizontal component of a table, consisting of a sequence of values, one for each column of the table. See also record.

row-begin column

A generated column that is defined with the AS ROW BEGIN clause. The value is assigned whenever a row is inserted into the table or any column in the row is updated. A row-begin column is intended for use as the first column of a SYSTEM_TIME period. See also generated column, row-end column, transaction-start-ID column.

row change timestamp column

A generated column that is defined with the AS ROW CHANGE TIMESTAMP clause. A row change timestamp column provides a way for the database manager to automatically generate and maintain a timestamp value for each row that is inserted or updated in a table. A table can have no more than one row change timestamp column.

row-end column

A generated column that is defined with the AS ROW END clause. The value is assigned whenever a row is inserted into the table or any column in the row is updated. A row-end column is intended for use as the second column of a SYSTEM_TIME period. See also generated column, row-begin column, transaction-start-ID column.

rowid

A value that uniquely identifies a row in a table and does not change.

row lock

A lock on a single row of data.

row-positioned fetch orientation

The specification of the desired placement of the cursor as part of a FETCH statement, with respect to a single row (for example, NEXT, LAST, or ABSOLUTE n). See also rowset-positioned fetch orientation.

rowset

A set of rows for which a cursor position is established.

rowset cursor

A cursor that is defined so that one or more rows can be returned as a rowset for a single FETCH statement and the cursor is positioned on the set of rows that is fetched.

rowset-positioned fetch orientation

The specification of the desired placement of the cursor as part of a FETCH statement, with respect to a rowset (for example, NEXT ROWSET, LAST ROWSET, or ROWSET STARTING AT ABSOLUTE n). See also row-positioned fetch orientation.

row trigger

A trigger whose granularity is defined by using the FOR EACH ROW clause.

RR

See repeatable read.

RRSAF

See Resource Recovery Services attachment facility.

RS

See read stability.

S

savepoint

A named entity that represents the state of data and schemas at a particular point in time within a unit of work.

SBCS

See single-byte character set.

SCA

See shared communications area.

scalar function

An SQL function that optionally accepts arguments and that returns a single scalar value each time that it is invoked. A scalar function can be referenced in an SQL statement wherever an expression is valid. See also function, routine.

scale

The number of digits in the fractional part of a number.

schema

A collection of database objects such as tables, views, indexes, or triggers that define a database. A schema provides a logical classification of database objects.

scrollability

A property of a cursor that indicates whether the cursor can fetch in a backward direction. See also fetch orientation.

scrollable cursor

A cursor that can be used to fetch in backward and forward directions. See also nonscrollable cursor.

search condition

A criterion for selecting rows from a table. A search condition consists of one or more predicates.

secondary authorization ID

In Db2 for z/OS, an authorization identifier that is associated with a primary authorization ID by an authorization exit routine. See also primary authorization ID.

secondary group buffer pool

For a duplexed group buffer pool, the structure that is used to back up changed pages that are written to the primary group buffer pool. No page registration or cross-invalidation occurs using the secondary group buffer pool. The z/OS equivalent is "new structure." See also primary group buffer pool.

secondary index

A nonpartitioning index on a partitioned table. See also nonpartitioned index.

section

The segment of a plan or package that contains the executable structures for a single SQL statement.

security label

A classification of users' access to objects or data rows in a multilevel security environment.

segment

A group of pages that hold rows of a single table. All segments in a table space are equal in size. See also segmented table space, universal table space.

segmented table space

A table space that is divided into equally sized segments. See also segment, universal table space.

self-referencing constraint

A referential constraint that defines a relationship in which a table is a dependent of itself.

self-referencing table

A table that is both a parent and a dependent table in the same referential constraint.

sensitive cursor

A cursor whose result table is affected by changes made to a database after the result table has been materialized. See also cursor, cursor sensitivity.

sequence

A database object that is independent of any one table that automatically generates unique key values based on initial user specifications.

sequential data set

A data set whose records are organized based on their successive physical positions, such as on magnetic tape. See also partitioned data set.

sequential prefetch

A mechanism that triggers consecutive asynchronous I/O operations. Pages are fetched before they are required, and several pages are read by using a single I/O operation.

serialized profile

A Java object, one or more of which are produced by the SQLJ translator, that contains SQL statements and descriptions of host variables. A serialized profile file is used to describe the SQL statements so that they can be run with either a JDBC-based or a customized runtime library.

server

The target of a request from a remote requester. In a Db2 database system, the server function is provided by the distributed data facility, which is used to access a Db2 database from remote applications.

service class

A group of work that has the same service goals or performance objectives, resource requirements, or availability requirements. For workload management, a service goal and, optionally, a resource group is assigned to a service class.

service request block (SRB)

A control block that represents a routine that performs a particular function or service in a specified address space.

session

A logical or virtual connection between two stations, software programs, or devices on a network that allows the two elements to communicate and exchange data for the duration of the session. See also SQL connection.

session protocol

The available set of SNA communication requests and responses.

set operator

An operator in SQL that corresponds to a relational operator. A set operator derives a result table by combining two other result tables. An example of a set operator is UNION, which corresponds to the union relational operator.

shared communications area (SCA)

A coupling facility list structure that a Db2 for z/OS data sharing group uses for communication between members of the data sharing group.

shared lock

A lock that limits concurrently running application processes to read-only operations on database data. See also exclusive lock, gross lock.

share lock

A lock that prevents concurrently executing application processes from changing data, but not from reading data. See also exclusive lock.

shift-in character

A control character (X'0F') that is used in EBCDIC systems to denote that the subsequent bytes represent single-byte character set (SBCS) characters. See also shift-out character.

shift-out character (SO)

A control character (X'0E') that is used in EBCDIC systems to denote that the subsequent bytes, up to the next shift-in control character, represent double-byte character set (DBCS) characters. See also shift-in character.

sign-on

A request made by an application process or terminal user to verify authorization to use resources.

sign on

To connect to a computer system or network.

simple page set

A nonpartitioned page set. A simple page set initially consists of a single data set (page set piece).

simple table space

A table space that is neither partitioned nor segmented.

single-byte character set (SBCS)

A coded character set in which each character is represented by a 1-byte code. A 1-byte code point allows representation of up to 256 characters. See also double-byte character set, multibyte character set.

single-precision floating-point number

A 32-bit approximate representation of a real number.

SMF

See System Management Facilities.

SNA

See Systems Network Architecture.

SNA network

The part of the user application network that conforms to the formats and protocols of Systems Network Architecture (SNA). The SNA network consists of network addressable units (NAUs), a gateway function, intermediate session routing function components, and the transport network.

SO

See shift-out character.

socket

A means for directing data to an application in a TCP/IP network using a unique identifier that is a combination of an IP address and a port number.

sourced function

A function that duplicates the semantics of another function, called a source function. Only scalar and aggregate functions can be sourced functions. See also function, routine, user-defined function.

source program

A set of host language statements and SQL statements that is processed by an SQL precompiler.

source table

A table that contains data that is to be replicated to a target table.

source type

An existing type that is used to internally represent a distinct type.

space

A sequence of one or more blank characters.

special register

A storage area that is defined for an application process by the database manager and is used to store information that can be referenced in SQL statements. Examples are USER and CURRENT DATE. See also built-in global variable.

specific function name

A particular user-defined function that is known to the database manager by its specific name. Many specific user-defined functions can have the same function name. When a user-defined function is defined to the database, every function is assigned a specific name that is unique within its schema. Either the user can provide this name, or a default name is used.

SPUFI

See SQL Processor Using File Input.

SQL

See Structured Query Language.

SQL authorization ID (SQL ID)

In Db2 for z/OS, the ID that is used for checking the authorization of dynamic SQL statements in some situations.

SQLCA

See SQL communication area.

SQL communication area (SQLCA)

A set of variables that provides an application program with information about the execution of its SQL statements, XQuery expressions, or requests from the database manager.

SQL connection

An association between an application process and a local or remote application server or database server. See also connection, session.

SQLDA

See SQL descriptor area.

SQL descriptor area (SQLDA)

A set of variables in a structure used in the processing of certain SQL statements that describe input variables, output variables, or the columns of a result table. The SQLDA is intended for dynamic SQL programs.

SQL escape character

The symbol that is used to enclose an SQL delimited identifier. This symbol is the double quotation mark (").

SQL function

A function that is implemented entirely by using a subset of SQL statements and SQL procedural language (SQL PL) statements. See also function, routine, user-defined function.

SQL ID

See SQL authorization ID.

SQLJ

See Structured Query Language for Java.

SQL path

An ordered list of schema names that is used to resolve unqualified references to user-defined functions, distinct types, and procedures.

SQL PL

See SQL Procedural Language.

SQL Procedural Language (SQL PL)

A language extension of SQL that consists of statements and language elements that can be used to implement procedural logic in SQL statements. SQL PL provides statements for declaring variables and condition handlers, assigning values to variables, and for implementing procedural logic.

SQL procedure

A user-written program that is implemented entirely by using a subset of SQL statements and SQL PL statements and that is invoked by using the SQL CALL statement. See also procedure, routine, SQL routine, user-defined procedure.

SQL processing conversation

Any conversation that requires access of Db2 for z/OS data, either through an application or by dynamic query requests. See also conversation.

SQL Processor Using File Input (SPUFI)

A facility of the TSO attachment subcomponent that enables the DB2I user to run SQL statements without embedding them in an application program.

SQL return code

The SQLSTATE or SQLCODE value that indicates whether the previously run SQL statement completed successfully, with one or more warnings, or with an error.

SQL routine

A function, method, or procedure that has its routine logic implemented entirely with SQL statements and SQL PL language elements and statements. See also routine, SQL procedure.

SQL schema

A collection of database objects such as tables, views, indexes, functions, user-defined types, or triggers that defines a database. An SQL schema provides a logical classification of database objects.

SQL statement coprocessor

An alternative to the Db2 for z/OS precompiler that can be used to process SQL statements at compile time. The user invokes an SQL statement coprocessor by specifying a compiler option.

SQL string delimiter

See string delimiter.

SRB

See service request block.

stand-alone

Pertaining to a program that can run separately from the Db2 database system, without using Db2 services.

star join

A method of joining a dimension column of a fact table to the key column of the corresponding dimension table. See also dimension table, join, star schema.

star schema

A type of relational database schema that is composed of a set of tables comprising a single, central fact table surrounded by dimension tables. See also dimension table, star join.

statement handle

The data object that contains information about an SQL statement or XQuery expression that is managed by the Db2 call level interface. Such information includes dynamic arguments, bindings for dynamic arguments and columns, cursor information, result values, and status information. Each statement handle is associated with a connection handle. See also connection handle, handle.

statement string

The character string form of a dynamic SQL statement.

statement trigger

A trigger that is defined with the trigger granularity FOR EACH STATEMENT.

static bind

A process by which SQL statements are bound after they are precompiled. All static SQL statements are prepared for execution at the same time. See also automatic bind, dynamic bind.

static cursor

A named control structure that does not change the size of the result table or the order of its rows after an application opens the cursor. See also cursor, dynamic cursor.

static IP address

A fixed IP address for a persistent device or logical unit on a network that uses the IP standard. See also IP address.

static SQL

SQL statements that are embedded within a program and are bound before the program is executed. After being bound, a static SQL statement does not change, although values of host variables specified by the statement can change. See also deferred embedded SQL, embedded SQL.

storage group

A named set of disks on which Db2 for z/OS data can be stored.

stored procedure

A user-written application program that can be invoked through the use of the SQL CALL statement.

string

In programming languages, the form of data used for storing and manipulating text.

string delimiter

A symbol that is used to enclose a string constant. The SQL string delimiter is the apostrophe (') except in COBOL applications, where the user assigns either a quotation mark (") or an apostrophe (').

strong typing

A process that prevents two objects with mismatched data types from being compared to each other and prevents data from being assigned to an object defined to accept data of a different type.

structure

A construct that uses z/OS to map and manage storage on a coupling facility.
A name that refers collectively to different types of Db2 objects, such as tables, databases, views, indexes, and table spaces.

Structured Query Language (SQL)

A standardized language for defining and manipulating data in a relational database.

Structured Query Language for Java (SQLJ)

A standard for embedding SQL in Java programs, defining and calling Java procedures and user-defined functions, and using database structured types in Java.

structure owner

In relation to group buffer pools, the Db2 member that is responsible for the following activities: coordinating rebuild, checkpoint, and damage assessment processing; and monitoring the group buffer pool threshold and notifying castout owners when the threshold has been reached

subcomponent

A group of closely related Db2 for z/OS modules that work together to provide a general function.

subject table

The table for which a trigger is created. When the defined triggering event occurs on this table, the trigger is activated.

subpage

The unit into which a physical index page can be divided.

subquery

A form of a fullselect that is enclosed within parentheses and used as a component of a query.

subselect

The form of a query that does not include a UNION, INTERSECT, or EXCEPT operator. Subselect query syntaxes can differ depending on the platform.

substitution character

A unique character that is substituted during character conversion for any characters in the source program that do not have a match in the target coding representation.

subsystem

In z/OS, a service provider that performs one or many functions but does nothing until a request is made. For example, each IBM MQ for z/OS queue manager or instance of a Db2 for z/OS database management system is a z/OS subsystem.

surrogate pair

A coded representation for a single character that consists of a sequence of two 16-bit code units, in which the first value of the pair is a high-surrogate code unit in the range U+D800 through U+DBFF, and the second value is a low-surrogate code unit in the range U+DC00 through U+DFFF. Surrogate pairs provide an extension mechanism for encoding an additional 1,048,576 characters without using any 32-bit code units.

SVC dump

A dump that is issued when a z/OS or a Db2 functional recovery routine detects an error.

sync point

See point of consistency.

sync point tree

The tree of recovery managers and resource managers that are involved in a logical unit of work, starting with the recovery manager, that make the final commit decision.

synonym

In SQL, an alternative name for a table view. Synonyms can be used to refer only to objects at the subsystem in which the synonym is defined. A synonym cannot be qualified and can therefore not be used by other users.

sysplex

A set of z/OS systems that communicate with each other through certain multisystem hardware components and software services.

sysplex query parallelism

Parallel execution of a single query that is accomplished by using multiple tasks on more than one Db2 for z/OS subsystem. See also query CP parallelism.

system administrator

A Db2 database user with administrative authority. In Db2 for Linux, UNIX, and Windows and in Db2 for z/OS, this authority is SYSADM. In Db2 for IBM i, this authority is *ALLOBJ.

system agent

A work request that Db2 for z/OS creates, such as prefetch processing, deferred writes, and service tasks. See also allied agent.

system authorization ID

The primary Db2 authorization ID that is used to establish a trusted connection. A system authorization ID is derived from the system user ID that is provided by an external entity, such as a middleware server.

system conversation

The conversation that two Db2 for z/OS subsystems must establish to process system messages before any distributed processing can begin.

system-defined routine

An object (function or procedure) for which system DBADM and SQLADM authorities have implicit execute privilege on the routine and any packages executed within the routine.

System Management Facilities (SMF)

A component of z/OS that collects and records a variety of system and job-related information.

system period

A pair of columns with system-maintained values that indicates the period of time when a row is valid. See also system-period data versioning, system-period temporal table.

system-period data versioning

Automatic maintenance of historical data by the database manager by using a system period. See also system period, system-period temporal table.

system-period temporal table

A table that is defined with system-period data versioning. See also bitemporal table, history table, system period, system-period data versioning.

Systems Network Architecture (SNA)

The description of the logical structure, formats, protocols, and operational sequences for transmitting information through and controlling the configuration and operation of networks.

T

table: In a relational database, a database object that consists of a specific number of columns and is used to store an unordered set of rows. See also base table, temporary table, view.
table-controlled partitioning: A type of partitioning in which partition boundaries for a partitioned table are controlled by values that are defined in the CREATE TABLE statement.
table function: A function that receives a set of arguments and that returns a table to the SQL statement that references the function. A table function can be referenced only in the FROM clause of a subselect. See also function, routine, user-defined function.
table locator: A mechanism that allows access to trigger tables in SQL or from within user-defined functions. A table locator is a fullword integer value that represents a transition table. See also transition table.
table space: A logical unit of storage in a database. In Db2 for z/OS, a table space is one or more page sets that stores data for one or more tables. In Db2 for Linux, UNIX, and Windows, a table space is a collection of containers, and the data, index, long field, and LOB portions of a table can be stored in the same table space or in separate table spaces. See also page set.
table space set: A set of table spaces and partitions that should be recovered together because the tables contained in the table spaces have dependencies on one another. The dependencies can, for example, be between parent table and descendent table or between base table and auxiliary table.
task control block (TCB): A z/OS control block that is used to communicate information about tasks within an address space that is connected to a subsystem. See also address space connection.
TB: See terabyte.
TCB: See task control block.
TCP/IP: See Transmission Control Protocol/Internet Protocol.
TCP/IP port: A 2-byte value that identifies a TCP/IP network application within a TCP/IP host.
template: A Db2 utilities output data set descriptor that is used for dynamic allocation. A template is defined by the TEMPLATE utility control statement.
temporal table: A table that records the period of time when a row is valid.
temporary table: A table that holds temporary data. Temporary tables are useful for holding or sorting intermediate results from queries that contain many rows. The two kinds of temporary tables, which are created by different SQL statements, are the created temporary table and the declared temporary table. See also base table, created temporary table, declared temporary table, result table, table.
terabyte (TB): For processor storage, real and virtual storage, and channel volume, 2 to the 40th power or 1 099 511 627 776 bytes. For disk storage capacity and communications volume, 1 000 000 000 000 bytes.
textual XML format: A representation of XML data that uses character values, an approach that allows for direct reading by people.
thread: The Db2 structure that describes the connection of an application, traces its progress, processes resource functions, and delimits its accessibility to Db2 resources and services. Most Db2 functions execute under a thread structure.
threadsafe: Pertaining to a function, macro, or operating system service that can be called from multiple threads in a process at the same time. See also reentrant code.
three-part name: The full name of a table, view, or alias that consists of a location name, an authorization identifier, and an object name, separated by periods.
time: A three-part value that designates a time of day in hours, minutes, and seconds. See also timestamp.
timeout: Abnormal termination of either an application or the Db2 for z/OS subsystem because of the unavailability of resources.
Time Sharing Option (TSO): A base element of the z/OS operating system with which users can interactively work with the system. See also Interactive System Productivity Facility.
timestamp: A seven-part value that consists of date and time. The timestamp is expressed in years, months, days, hours, minutes, seconds, and fractional seconds. See also time.
timestamp with time zone: A two-part value that consists of a timestamp and time zone. The timestamp with time zone is expressed in years, months, days, hours, minutes, seconds, microseconds, time zone hours, and time zone minutes.
trace: A Db2 for z/OS facility that provides the ability to collect monitoring, auditing, performance, accounting, statistics, and serviceability (global) data.
transaction: An atomic series of SQL statements that make up a logical unit of work. All of the data modifications made during a transaction are either committed together as a unit or rolled back as a unit.
transaction lock: A lock that is used to control concurrent execution of SQL statements.
transaction program name: In SNA LU 6.2 conversations, the name of the program at the remote logical unit that is to be the other half of the conversation.
transaction-start-ID column: A generated column that is defined with the AS TRANSACTION START ID clause. The value is assigned whenever a row is inserted into the table or any column in the row is updated. A transaction-start-ID column is intended for use in a system-period temporal table. See also generated column, row-begin column, row-end column.
transition table: A temporary table that contains all of the affected rows of a subject table in their state before or after a triggering event occurs. Triggered SQL statements in the trigger definition can reference the table of changed rows in the old state or the new state. See also table locator.
transition variable: A variable that is valid only in FOR EACH ROW triggers. It allows access to the transition values for the current row. An old transition variable is the value of the row before the modification is applied, and the new transition variable is the value of the row after the modification is applied.
Transmission Control Protocol/Internet Protocol (TCP/IP): An industry-standard, nonproprietary set of communication protocols that provides reliable end-to-end connections between applications over interconnected networks of different types.
tree: A data structure whose elements are linked in a hierarchical fashion.
trigger: A database object that is associated with a single base table or view and that defines a rule. The rule consists of a set of SQL statements that runs when an insert, update, or delete database operation occurs on the associated base table or view. See also after trigger, before trigger, delete trigger, insert trigger, instead of trigger, trigger activation, trigger activation time, trigger granularity, update trigger.
trigger activation: The process that occurs when the trigger event that is defined in a trigger definition is executed. Trigger activation consists of the evaluation of the triggered action condition and conditional execution of the triggered SQL statements. See also after trigger, before trigger, trigger, trigger activation time.
trigger activation time: An indication in a trigger definition of whether the trigger should be activated before or after a trigger event. See also after trigger, before trigger, trigger, trigger activation.
trigger body: The set of triggered SQL statements that is run when a trigger is activated and its triggered action condition evaluates to true. See also triggered action, triggered action condition, triggered SQL statement.
trigger cascading: The process that occurs when the triggered action of a trigger causes the activation of another trigger.
triggered action: The SQL logic that is performed when a trigger is activated. The triggered action consists of an optional triggered action condition and a set of triggered SQL statements that is run only if the triggered action is true. See also trigger body, triggered action condition, triggered SQL statement.
triggered action condition: An optional part of a triggered action. This Boolean condition is defined by a WHEN clause and specifies a condition that is evaluated to determine whether the triggered SQL statements should be run. See also trigger body, triggered action, triggered SQL statement.
triggered SQL statement: One of a set of SQL statements that is run when a trigger is activated and its triggered action condition evaluates to true. The set of triggered SQL statements is also called the trigger body. See also trigger body, triggered action, triggered action condition.
trigger granularity: In SQL, the characteristic of a trigger that determines whether the trigger is activated only once for the triggering SQL statement or once for each row that the SQL statement modifies. See also trigger.
triggering event: The specified operation in a trigger definition that causes the activation of that trigger. The triggering event is comprised of a triggering operation (insert, update, or delete) and a subject table or view on which the operation is performed.
triggering SQL operation: The SQL operation that causes a trigger to be activated when the operation is performed on the subject table.
trigger package: In Db2 for z/OS, a package that is created when a CREATE TRIGGER statement is executed. The package is executed when the trigger is activated.
trust attribute: An attribute upon which to establish trust. A trusted relationship is established based on one or more trust attributes.
trusted connection: A database connection whose attributes match the attributes of a unique trusted context that is defined at the database server.
trusted connection reuse: The ability to switch the current user ID on a trusted connection to a different user ID.
trusted context: A database security object that enables the establishment of a trusted relationship between a database management system and an external entity.
trusted context default role: The role that is inherited by all users of a trusted context unless it is overridden by a user-specific role in the trusted context definition. See also trusted context user-specific role.
trusted context user: A user ID to which switching the current user ID on a trusted connection is permitted.
trusted context user-specific role: A role that is associated with a specific trusted context user. It overrides the trusted context default role if the current user ID on the trusted connection matches the ID of the specific trusted context user. See also trusted context default role.
trusted relationship: A privileged relationship between two entities such as a middleware server and a database server. This relationship allows for a unique set of interactions between the two entities that would be impossible otherwise.
TSO: See Time Sharing Option.
TSO attachment facility: A Db2 facility consisting of the DSN command processor and DB2I. Applications that are not written for the CICS or IMS environments can run under the TSO attachment facility.
type-2 index: An index that supports marking an index entry as pseudo deleted.
typed parameter marker: A parameter marker that is specified along with its target data type. It has the general form CAST (? AS data type). See also parameter marker, untyped parameter marker.

U

UCS: See universal character set.
UCS-2: Universal Character Set, coded in 2 octets, which means that each character is represented by 16 bits. UCS-2 is a subset of UTF-16. See also UTF-16, UTF-8.
UDF: See user-defined function.
UDT: See user-defined data type.
uncommitted read (UR): An isolation level under which a query in a transaction can read any rows, even if there are uncommitted changes to those rows made by statements in other transactions. The UR isolation level is upgraded to CS when data is being modified. See also cursor stability, isolation level, read stability, repeatable read.
underlying view: The view on which another view is directly or indirectly defined.
undo: A state of a unit of recovery that indicates that the changes that the unit of recovery made to recoverable Db2 resources must be backed out.
Unicode: A character encoding standard that supports the interchange, processing, and display of text that is written in the common languages around the world, plus many classical and historical texts. See also multibyte character set.
union: An SQL operation that combines the results of two select statements. Unions are often used to merge lists of values that are obtained from several tables.
unique constraint: The rule that no two values in a primary key or key of a unique index can be the same. See also constraint.
unique index: An index that ensures that no identical key values are stored in a column or a set of columns in a table.
unit of recovery: A recoverable sequence of operations within a single resource manager, such as an instance of Db2 for z/OS. See also unit of work.
unit of work (UOW): A recoverable sequence of operations within an application process. At any time, an application process is a single UOW, but the life of an application process can involve many UOWs as a result of commit or rollback operations. In a multisite update operation, a single UOW can include several units of recovery. See also multisite update, unit of recovery.
universal character set (UCS): The ISO standard that allows all data to be represented as 2 bytes (UCS-2) or 4 bytes (UCS-4). Encoding in the UCS-2 form can accommodate the necessary characters for most of the written languages in the world.
universal table space (UTS): A table space that has partitions and segmented organization, including partition-by-range and partition-by-growth table spaces. See also partition, partition-by-growth table space, partitioned table space, range-partitioned table space, segment, segmented table space.
unlock: To release an object or system resource that was previously locked and return it to general availability.
untyped parameter marker: A parameter marker that is specified without its target data type. See also parameter marker, typed parameter marker.
UOW: See unit of work.
updatability: The ability of a cursor to perform positioned updates and deletes. The updatability of a cursor can be influenced by the SELECT statement and the cursor sensitivity option that is specified on the DECLARE CURSOR statement.
update hole: The location on which a cursor is positioned when a row in the result table is fetched again but values in the underlying tables have been updated such that the row no longer satisfies the search condition. See also delete hole, hole.
update trigger: A trigger that is activated by an update operation on the table or view that is specified in the trigger definition. See also delete trigger, insert trigger, instead of trigger, trigger.
UR: See uncommitted read.
user-defined data type (UDT): A data type that is defined to the Db2 database system by using the CREATE TYPE statement, and can be referenced thereafter in SQL statements. See also distinct type.
user-defined function (UDF): A function that is defined to the Db2 database system by using the CREATE FUNCTION statement and that can be referenced thereafter in SQL statements. See also built-in function, external function, function, routine, sourced function, SQL function, table function.
user-defined global variable: A global variable that is defined to the Db2 database system by using the CREATE VARIABLE statement and that can be referenced thereafter in SQL statements. See also built-in global variable.
user-defined procedure: A procedure that is defined to the Db2 database system by using the CREATE PROCEDURE statement and that can be referenced thereafter in SQL statements. See also external procedure, procedure, routine, SQL procedure.
user view: In logical data modeling, a model or representation of critical information that a business requires.
UTF-16: Unicode Transformation Format, 16-bit encoding form, which is designed to provide code values for over a million characters and is a superset of UCS-2. The CCSID value for data in UTF-16 format is 1200. See also UCS-2, UTF-8.
UTF-8: Unicode Transformation Format, 8-bit encoding form, which is designed for ease of use with existing ASCII-based systems. The CCSID value for data in UTF-8 format is 1208. See also UCS-2, UTF-16.
UTS: See universal table space.

V

value: The smallest unit of data manipulated in SQL.
variable: A representation of a changeable value.
variant function: See non-deterministic function.
varying-length string: A character, graphic, or binary string with a length that is not fixed but that can range within set limits.
version: A member of a set of similar programs or packages and, in Db2 for z/OS, similar database request modules (DBRMs) or large objects (LOBs).
view: A logical table that is based on data stored in an underlying set of tables. The data returned by a view is determined by a SELECT statement that is run on the underlying tables. See also base table, table.
Virtual Storage Access Method (VSAM): An access method for direct or sequential processing of fixed-length and variable-length records on disk devices. The records in a VSAM data set or file can be organized in logical sequence by a key field (key sequence), in the physical sequence in which they are written on the data set or file (entry sequence), or by relative-record number.
Virtual Telecommunications Access Method (VTAM): An IBM licensed program that controls communication and the flow of data in an SNA network.
volatile table: A table whose cardinality can vary significantly over relatively short periods of time. Compared to statistics that are collected for non-volatile tables, statistics that are collected for volatile tables are less likely to represent the actual data in the tables. The optimizer takes this situation into account when determining access plans involving a volatile table.
VSAM: See Virtual Storage Access Method.
VTAM: See Virtual Telecommunications Access Method.

W

warm start: The normal Db2 restart process, which involves reading and processing log records so that data that is under the control of Db2 is consistent. See also cold start.
WLM application environment: A z/OS Workload Manager attribute that is associated with one or more procedures. The WLM application environment determines the address space in which a given procedure runs.
WLM enclave: A construct that can span multiple dispatchable units (service request blocks and tasks) in multiple address spaces, allowing them to be reported on and managed by Workload Manager (WLM) as part of a single work request.
write to operator (WTO): A system service used to send messages to an operator console informing the operator of errors or system conditions that might need correcting. A response is not required.
WTO: See write to operator.

X

XCF: See cross-system coupling facility.
XES: See cross-system extended services.
XML: See Extensible Markup Language.
XML attribute: A name-value pair within a tagged XML element that modifies certain features of the element.
XML column: A column of a table that stores XML values and is defined using the SQL built-in data type XML.
XML data type: A data type for XML values.
XML element: A logical structure in XML that is delimited by a start tag and an end tag.
XML index: An index on an XML column that provides efficient access to nodes within an XML document by providing index keys that are based on XML patterns.
XML lock: A column-level lock for XML data. The operation of XML locks is similar to the operation of LOB locks.
XML node: The smallest unit of valid, complete structure in a document. For example, a node can represent an element, an attribute, or a text string.
XML node ID index: An implicitly created index, on an XML table that provides efficient access to XML documents and navigation among multiple XML data rows in the same document.
XML pattern: A slash-separated list of element names that describes a path through an XML document and through specific node characteristics. The pattern selects elements that match the specifications. XML patterns are specified to create indexes on XML columns in a database.
XML publishing function: A function that returns XML values from SQL values.
XML schema: A mechanism for describing and constraining the content of XML files by indicating which elements are allowed and in which combinations. XML schemas are an alternative to document type definitions (DTDs) and can be used to extend functionality in the areas of data typing, inheritance, and presentation.
XML schema repository (XSR): A repository that allows the Db2 database system to manage dependencies on externally referenced XML artifacts in XML instance documents within a database. Supported XSR objects include XML schemas, document type definitions (DTDs), and other external entities. When registered with the XSR, these objects have a unique identifier and can be used to validate XML instance documents.
XML serialization function: A function that returns a serialized XML string from an XML value.
XML table: An auxiliary table that is implicitly created when an XML column is added to a base table. This table stores the XML data and the column in the base table points to it.
XML table space: A table space that is implicitly created when an XML column is added to a base table. The table space stores the XML table. If the base table is partitioned, one partitioned table space exists for each XML column of data.
X/Open: An industrial consortium that produces specifications and test suites to resolve incompatibilities among different computer systems and software components.
XRF: See extended recovery facility.
XSR: See XML schema repository.

Z

z/OS: An IBM mainframe operating system that uses 64-bit real storage.