General flow of CICS EXEC commands within a CICS application

The design of a CICS® application program using the CICS EXEC command level application programming interfaces is determined by whether the transaction being sent on the ISC session is to be processed using SEND/RECEIVE, SEND LAST, or START/RETRIEVE.

The sequence of EXEC commands issued is determined by whether the transaction is defined as recoverable or nonrecoverable. Program design can also depend on whether CICS is the front-end system (initiating a transaction) or back-end system (replying to an IMS transaction).

This topic presents an overview of synchronous and asynchronous transaction processing flow within CICS. Understanding the content and functions of the ATTACH and SCHEDULER FM headers is helpful in understanding this topic.