Chapter 20. Customizing IMS

Customizing IMS is the process of tailoring IMS functions to fit the specific needs of your installation.

Some customization tasks are required before you can use IMS, but most are optional. If you elect not to do optional customization on a specific IMS function, that function then works according to IBM-provided defaults. If IMS is new to your installation, you initially might want to do a minimum amount of optional customization. You can use IMS and you can do additional customization when performance or IMS capabilities indicate the need to do so.

There are a number of ways for you to customize IMS. IMS provides:

• Initialization values you can change.

• Macros you can use.

• Procedures you can change.

• User exits (places in IMS's logic flow) for which you can write exit routines to perform special processing. IMS calls exit routines at various points and allows you to control how IMS performs its work.

One example of customizing might be to interrogate an in-flight message (in an MSC environment) to determine if it originated from a test or production system. If it came from a test system, you might want to route that message to an application that collects data about the test system. If the message originated from a production system, you probably would not want to change its destination.

To perform the interrogation of the message, you would code a TM and MSC Message Routing and Control User Exit routine. If you name this routine DFSMSCE0, place it in the IMS.SDFSRESL library, and bind it to that library (or a concatenated library), IMS calls your exit routine when IMS receives the message. When your exit routine is done with its processing, the exit routine returns control to IMS and then IMS resumes processing the message to either the original destination or the test application.

Certain exit routines are required and others are optional. Some IBM-supplied exit routines can be used as is and some require modification before using.

Recommendation:

Write IMS exit routines in assembler language rather than high-level languages. IMS does not support exit routines running under Language Environment for z/OS. If an exit routine is written in a high-level language executing in the Language Environment for z/OS, you might incur performance problems or abends.

In This Chapter:

• "What You Can Customize"

• "Naming the Routines" on page 349

• "Changeable Interfaces and Control Blocks" on page 349

• "IMS Standard User Exit Parameter List" on page 349

• "Binding the Routines" on page 349

• "Saving Registers" on page 350

• "IMS Callable Services" on page 350

• "Considering Performance" on page 351

• "Summary of IMS Exit Routines" on page 352