Editing messages

Within IMS, the communication interface is transparent to application programs.

In support of this, IMS provides some common editing that:
  • Appends protocols and function management headers to outbound messages
  • Strips function management headers from incoming messages and moves the messages to appropriate points within the IMS control blocks
Subsequent to this common editing, messages received by IMS are edited by ISC edit, Message Format Service (MFS), or basic edit in accordance with the input ATTACH or SCHEDULER DPN parameter. Messages sent by IMS are edited by Message Format Service before they are sent. The edit functions of ISC edit and basic edit are unique. However, the associated protocols are the same.
  • ISC edit is the default editor. When ISC edit is requested and that request does not contain the SNA-defined PRN parameter following the input data, the message is edited with partial input data transparency. That is, only the IMS-required destination code and optional password, which must occur at the beginning of the message, are subjected to editing by ISC edit. The balance of the input message is not edited prior to processing unless the transaction is defined to translate to uppercase. Full input data transparency is provided through ISC edit using the SNA-defined PRN parameter on the ATTACH or SCHEDULER FM header. This enables the IMS transaction code to be external to the message and enables IMS to receive input and route it to its proper destination (terminal or transaction) without examining the input message itself. Because the transaction code is external to the data stream, the optional password is not available to the session. Therefore, password security should not be defined. If password security is defined, an error results.
  • Message Format Service's Distributed Presentation Management (DPM) option divides responsibility for message formatting between MFS and a program residing in another subsystem. When using DPM-Bn, physical terminal characteristics are not defined to MFS. Instead, IMS sends MFS-formatted data to a program in the other subsystem. That program must complete the formatting, if necessary, and present the data to the physical device. DPM also allows user involvement in specifying input and output ISC message routing parameters. You can also use the PRN parameter on the ATTACH or SCHEDULER FM header to specify the IMS destination externally, relative to the resulting MFS-formatted input data stream.
  • Basic edit provides standard editing for terminal input. It is used to edit device and operator control characters and can be used in an ISC session when it is important to maintain input compatibility for existing applications. Protocols for basic edit are the same as those for ISC edit. Use of the ATTACH or SCHEDULER FM header PRN parameter has no effect when basic edit is used. The message destination is determined from the first field of the input data stream.

IMS permits basic edit, ISC edit, or MFS to be invoked in order to handle communication of transactions, commands, and message switches. MFS DPM facilities are defined as optional on a component-by-component basis. Any of these available processes are selectable on a message-by-message basis by using the ATTACH or SCHEDULER FM header.

ISC input and output can be edited by most IMS data communication exit routines. The exceptions are the MSC-related exit routines, and the hardware-required routines.