CICS locates the application program associated with the transaction, loads it into storage by utilizing tables such as PCT,PPT and RCT etc... and if i am correct all these resource definitions are moved to CSD file. i got the information how transaction identify the program when cics used to read the PCT,PPT and RCT tables etc. now what i am unable to understand/get the information is how transaction identify the program and load into storage when all the cics resources are available in csd file.
thanks in advance...
Joined: 14 Jan 2008 Posts: 2504 Location: Atlanta, Georgia, USA
The CSD is read by CICS Internals, the requested Transaction-Id is located (this is defined to the PCT entry), the program associated with the Transaction-Id is determined (this is defined to the PCT entry as well), then the PPT entry is located and the program is launched.
If PPT-Autoinstall is being used (Dynamic PPT) and this is the first-time program-usage, the Autoinstall-Exit builds the PPT entry and the process continues.
I won't get into the real technical aspects of the CICS Internals, but from a rudimentary standpoint, this should be all you need.
Joined: 06 Jun 2008 Posts: 8555 Location: Dubuque, Iowa, USA
When you define a transaction, be it through RDO or PCT (which is now obsolete, by the way), you MUST provide two critical pieces of information: the transaction code (4 characters) and the program associated with the transaction. When an otherwise unused terminal gives data to CICS (via ENTER key or PA key or PF key or ....), the first four characters CICS gets are the transaction. CICS looks up that transaction, identifies the associated program, and if it is not in memory CICS loads it, then executes that program. This is a grossly simplified explanation but it should resolve your question.