A transaction (task) may use several programs in the course of completing its work.
The installed program definition contains one entry for every program used by any application in the CICS system. Each entry holds, among other things, three particularly important pieces of information:
The language in which the program is written, which CICS needs to know in order to set up its linkages and control blocks properly
How many tasks are using the program at the moment
Where the program is (in main storage and/or on disk)
The installed transaction definition has an entry for every transaction identifier in the system (using “transaction” in the CICS sense of the word). The important information kept about each transaction is the transaction identifier and the name of the first program to be executed on behalf of the transaction.
You can see how these two sets of definitions work in concert:
The user types in a transaction identifier at the terminal (or the previous transaction may have determined it).
CICS looks up this identifier in the list of installed transaction definitions.
This tells CICS which program to invoke first.
CICS looks up this program in the list of installed program definitions, finds out where it is, and loads it if it isn’t already in main storage.
CICS builds the control blocks necessary for this transaction, using information from the definition of the transaction, program, and principle facility. For programs in ...