Connecting and Disconnecting Subsystems

Before an IMS subsystem can access databases in an external subsystem (another program executing in a z/OS address space) such as DB2, you must connect the IMS subsystem to this other subsystem. IMS can connect to another subsystem only if that subsystem is identified in the subsystem member in IMS.PROCLIB. Specify the subsystem member name in the SSM EXEC parameter. When specified to and accessed by IMS, the subsystem member name cannot be changed without stopping IMS.

Related Reading: For information on the SSM EXEC parameter, see IMS Version 9: Installation Volume 2: System Definition and Tailoring.

Connections between an IMS subsystem and another subsystem can occur with or without operator intervention, and without regard to which subsystem is available first.

• Automatic connection: When the SSM EXEC parameter is specified, IMS automatically establishes the connection when it processes the parameter.

• Operator-controlled connection: When the SSM EXEC parameter is not specified, the connection is established when the /START SUBSYS SSM command is entered. The /START SUBSYS SSM command specifies the subsystem member in IMS.PROCLIB that IMS uses to connect to subsystems.

Disconnecting IMS from another subsystem is initiated with the /STOP SUBSYS command, and normally completes without operator intervention. IMS quiesces all dependent region external subsystem activity prior to stopping the subsystem.