Chapter 17. Using and writing WebSphere MQ-CICS bridge applications for z/OS

Throughout this chapter the terms "CICS bridge" and "bridge" mean "WebSphere MQ-CICS bridge".

Most CICS applications were developed when a 3270 terminal was the main way of interacting with users. To use these applications with new transport mechanisms, such as WebSphere MQ, CICS recommends that applications are written with the business logic of the application separated from the presentation logic. The business logic can be accessed by a CICS Distributed Program Link (DPL) request to run the program. However, not all applications can be restructured in this way, for example when the customer does not own the source code of the application. The CICS bridge protects the investment in these legacy applications by allowing them to be accessed from other platforms. This makes CICS resources readily available to programs not running under CICS. This can be done for DPL programs and for 3270 transactions.

A WebSphere MQ application can start a CICS application by sending a structured message to the CICS bridge request queue. Any data required by the CICS application can be included in the request message:

• For DPL programs, the data required is the CICS communication area (COMMAREA) data used by the application.
• For 3270 transactions, the data required is vectors describing the Application Data Structures (ADSs) used by the application.

Similarly, the CICS application can send data back to the WebSphere MQ application in a message that is sent to a reply queue:

• For DPL programs, the data sent back is the COMMAREA data output by the application.
• For 3270 transactions, the data sent back is vectors describing the Application Data Structures (ADSs) output by the application.

The WebSphere MQ application can run on any platform, but the bridge request queue must reside on the local z/OS queue manager that is connected to the CICS adapter.

This chapter describes how to use and design WebSphere MQ-CICS bridge applications, under these headings:

• Using CICS DPL programs with the bridge
• Using CICS transactions with the bridge
• Programming for the distributed environment
• From 3270 legacy to 3270 bridge - an example
• Setting fields in the MQMD and MQCIH structures
• Setting the open options and put message options for the bridge request queue
• Managing MsgId and CorrelId in a unit of work
• Error handling by the CICS bridge
• Debugging CICS bridge applications
• Application data structure terminology