In order to manage the subsystems, DSSM requires information in the form of a declaration. This declaration determines which main components and satellites belong to a subsystem, how the subsystem can be activated, and how to set up interfaces to it. Thus, anyone creating a declaration must be familiar with the subsystem concerned. For this reason the necessary declarations for all DSSM-compatible subsystems are supplied in a declaration file.
Depending on the declaration, DSSM activates the subsystem and sets up interfaces and relations to other subsystems and to DSSM itself. Interfaces to a subsystem can be monitored by DSSM. In this way it is possible to deactivate the subsystem under the control of DSSM. If the interfaces are not monitored, the subsystem itself is responsible for deactivation.
The declarations are not given as operands in every DSSM call, as this would be too complicated and excessive. The declarations are specified using SSCM and are stored in the subsystem catalog, because
these declarations are stable and rarely change
these declarations are complex and extensive
these declarations must frequently be accessed by DSSM
not only internal subsystem information exists, but also cross-subsystem information.
The declarations of all subsystems belonging to a configuration (= declaration state) make up the SSMCAT subsystem catalog and are stored in a PAM file. This file is read in on startup and remains in memory until system shutdown. The ADD-SUBSYSTEM command can be used to extend the catalog during a session.
The LOAD-LOCAL-SUBSYSTEM-CATALOG command can be used to read the catalog and dynamically load it into the user address space of the calling task.