Wednesday, April 18, 2007

Review topic: CICS, misc capabilities

The RETRIEVE command gets data passed to it from a (previous) starting task, usually from a Queue named in the START command in the starting task.. Asynchronous processing may result on a remote system from a START. On the other hand, Distrubuted Transaction Processing (DTP) simulates a client-server relationship (front and back end).

The ENQ and DEQ command single thread requests (like printing) in a manner conceptually similar to the UPDATE option on the READ statement.

To access storage other than that provided in the linkage section, use the GETMAIN command.

The SYNCPOINT command commits updates, and they are not backed out or rolled back even if there is an abend.

An MRO is a Multi-Region Operation, with a File Owning Region, Application Owning Region, and Terminal Owning Region. Intersystem Communications (ISC) provides for systems on different machines (processors) communicate. ISC’s can enable groups of MRO’s to talk to one another, as could be shown by Venn-like diagrams.

The CRTE command connects a terminal owned by one CICS system to another system.

With function shipping, a concept that often comes up in writing system specs, a command on one system accesses a resource on another. The most common example is a READ or update on a VSAM file whose FCT entry indicates that the file is on another system (SYSID). The application READ command will need to process DFHRESP(SYSIDERR) which will usually mean that the remote system is not up.

EXCI, the External CICS interface, provides the ability to execute CICS programs from a batch program with a CICS LINK. This feature could be useful in quality assurance mass testing of many transactions and looking at the results on a log. We used a similar facility with Datacomm DC at Chilton in the 1980s to test implementations.

CICS web support can provide a sockets listener task to communicate with an HTTP converter, or it can provide its own transaction gateway in Java, with less robust graphics. But XML has become a more flexible way to teleport data to web applications.

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