Writing your program

 

The coding required to handle IMS™ transactions through WebSphere MQ depends on the message format required by the IMS transaction and the range of responses it can return. However, there are several points to consider when your application handles IMS screen formatting information.

When an IMS transaction is started from a 3270 screen, the message passes through IMS Message Format Services. This can remove all terminal dependency from the data stream seen by the transaction. When a transaction is started through OTMA, MFS is not involved. If application logic is implemented in MFS, this must be re-created in the new application.

In some IMS transactions, the end-user application can modify certain 3270 screen behavior, for example, highlighting a field that has had invalid data entered. This type of information is communicated by adding a two-byte attribute field to the IMS message for each screen field that needs to be modified by the program.

Thus, if you are coding an application to mimic a 3270, we need to take account of these fields when building or receiving messages.

You might need to code information in your program to process:

• Which key is pressed (for example, Enter and PF1)

• Where the cursor is when the message is passed to your application

• Whether the attribute fields have been set by the IMS application

  • High, normal, or zero intensity

  • Color

  • Whether IMS is expecting the field back the next time that Enter is pressed

• Whether the IMS application has used null characters (X'3F') in any fields.

If your IMS message contains only character data (apart from the LLZZ-data segment), and you are using an MQIIH structure, set the MQMD format to MQFMT_IMS and the MQIIH format to MQFMT_IMS_VAR_STRING.

If your IMS message contains only character data (apart from the LLZZ-data segment), and you are not using an MQIIH structure, set the MQMD format to MQFMT_IMS_VAR_STRING and ensure that your IMS application specifies MODname MQFMT_IMS_VAR_STRING when replying. If a problem occurs (for example, user not authorized to use the transaction) and IMS sends an error message, this has an MODname of the form DFSMOx, where x is a number between 1 and 5. This is put in the MQMD.Format.

If your IMS message contains binary, packed, or floating point data (apart from the LLZZ-data segment), code your own data-conversion routines. Refer to IMS/ESA Application Programming: Transaction Manager for information about IMS screen formatting.

• Writing WebSphere MQ applications to invoke IMS conversational transactions
  

• Triggering
  

• Writing programs containing IMS commands
  

 

Parent topic:

Writing WebSphere MQ-IMS bridge applications

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