APPC/IMS application program interface

Implicit API

The implicit API is an extension of the IMS standard DL/I API (call xxxTDLI). It allows IMS application programs to communicate with LU 6.2 application programs without being sensitive to LU 6.2 protocols and without requiring the programmer to have any knowledge of LU 6.2. APPC/IMS provides functions not normally available to an LU 6.2 application program: message queuing, and automatic asynchronous message delivery and recovery. Existing IMS transactions use the implicit API to communicate with APPC.

Implicit API messages are placed on the IMS message queues or the Fast Path expedited message handling (EMH) buffers for Fast Path transactions. The originating IMS determines whether to mark the input messages as discardable or nondiscardable.

When the implicit API is used, IMS issues all required CPI Communications calls. The application program interacts strictly with the IMS message queues or the Fast Path EMH buffers.

Explicit API

The explicit API is the CPI Communications API and is available to any IMS application program. The application program makes calls to APPC using the CPI Communications interface without using IMS. These CPI calls are handled directly by APPC/MVS™. Messages sent or received by the CPI Communications interface are not stored on the IMS message queues or in the EMH buffers, and these messages are not available for transaction restart. No IMS-provided functions are involved for these messages.

Alternatively, you can also use z/OS® the ATBxxxx calls of the APPC/MVS TP services. For information on using these calls, see z/OS MVS Programming: Writing Transaction Programs for APPC/MVS.