For CICS or IMS screen service interfaces, operations can specify any of the following:
- Active Screen
- The screen that the operation is intended to process. It contains the fields you use in the operation. This screen appears in the CICS or IMS screen pane of the Interface Mapper when you are defining the operation. The operation that is intended to be performed first has no active screen. Typically, the operation that is performed first starts an application using a transaction ID.
- Previous Screen
- The screen that is presented immediately before the active screen is presented during execution of the service. Most of the time, you should set this to ANY SCREEN (see below). Specifying a particular previous screen is only important when you want to interact with a screen differently depending on which screen preceded it. In this case, you would create multiple operations with the same active screen and differentiate them by specifying a particular previous screen for one or more of the operations.
- Transaction ID
- After any interaction with the active screen, this starts a new transaction using the ID specified. Most operations do not have a transaction ID. When you do not specify a transaction ID, the operation returns to the application with any data for the active screen.
It is common practice for COBOL IMS applications to specify a transaction ID in the MFS MID definition. In this case, to ensure that offsets are calculated properly, select the USE TRANSACTION ID FROM SCREEN DEFINITION option when specifying the transaction ID for your operation.
Active and previous screens can be derived from a map included in your project, or one of the following special screens:
- EMPTY SCREEN
- A screen that is devoid of any fields. For example, you can specify EMPTY SCREEN for the screen that appears after executing an operation that clears the screen.
- TEXT-SENT SCREEN
- A screen that appears as a result of the application executing a SEND TEXT command (CICS only).
- ANY SCREEN
- Indicates that the screen can be any screen and that the specification of a particular screen is either unnecessary or irrelevant to the operation.
You can also opt to automatically create default mappings between interface fields and all of the fields on the active screen.
In general, you want to create an initial operation to start your application. This operation consists of only a name and the transaction ID that starts the application. We recommend you use an operation name that clearly identifies this operation, such as
Start.
Note: Service interfaces written for IMS conversational applications must include an operation that enables the service to gracefully exit the application and ensure that the application’s state is properly maintained and that its SPA is properly cleared. While this type of operation is not required for other types of service interfaces, it is good practice to include one.
