IMS DB is a DBMS that helps you organize business data with both program and device independence.

Hierarchical databases and data manipulation language (DL/I calls) are at the heart of IMS DB. Data within the database is arranged in a tree structure, with data at each level of the hierarchy related to, and in some way dependent upon, data at the higher level of the hierarchy. Figure 1 shows the hierarchical database model. In a hierarchical database, data is stored within the database only once. The data item is then available to any user who is authorized to use it. Users do not need to have personal copies of the data.

Figure 1. Hierarchical Database Model

With IMS DB, you can:

• Maintain data integrity. The data in each database is guaranteed to be consistent and guaranteed to remain in the database even when IMS DB is not running.
• Define the database structure and the relationships among the database elements.
• Provide a central point of control and access for the IMS data that is processed by IMS applications.
• Perform queries against the data in the database.
• Perform database transactions (inserts, updates, and deletes) as a single unit of work so that the entire transaction either occurs or does not occur.
• Perform multiple database transactions concurrently with the results of each transaction kept isolated from the others.
• Maintain the databases. IMS DB provides facilities for tuning the databases by reorganizing and restructuring them.

Additionally, IMS DB lets you adapt IMS databases to the requirements of varied applications. Application programs can access common and, therefore, consistent data, thereby reducing the need to maintain the same data in multiple ways in separate files for different applications.

IMS databases are accessed internally using a number of IMS's database organization access methods. The actual database data is stored on disk storage using normal z/OS access methods. See the complete version of An Introduction to IMS.

IMS DB provides access to these databases from applications running under:

• IMS Transaction Manager
• CICS Transaction Server for OS/390® and z/OS
• z/OS batch jobs
• WebSphere Application Server for z/OS
• DB2 UDB for z/OS stored procedures