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In many cases, prerequisite criteria must be satisfied before the status of an object is changed (for example, VTAM must be up before CICS can be activated).
It is therefore necessary to provide Control-O/COSMOS with appropriate prerequisite information so that Control-O/COSMOS can ensure that prerequisites are satisfied before changing the status of an object. This prerequisite information is stored in the Prerequisite database. Each row in the Prerequisite database describes an object that must be up before another specified object is brought up.
Before attempting to change the (current) status of an object, Control-O/COSMOS checks the Prerequisite database for prerequisite criteria that must be satisfied.
If all prerequisites for changing the object’s status are satisfied (or if there are no prerequisites), Control-O/COSMOS triggers a rule that modifies the object’s status.
If certain prerequisites are not satisfied, the change is not performed at that time (for example, if VTAM is not up, CICS is not started). Control-O/COSMOS, however, continues to scan the Object and Prerequisite databases. This is important because environments are dynamic, and a prerequisite that is not satisfied at one point in time may be satisfied at a later time. (If, for example, VTAM is brought to an UP status, and therefore the prerequisites for starting CICS are satisfied, Control-O/COSMOS starts CICS the next time it scans the databases.)
All objects referenced in the Prerequisite database must be Control-O/COSMOS-controlled objects (meaning, objects defined in a Control-O/COSMOS Object database).
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