SPECIAL SERVICES OF FILE CONTROL - IBM Mainframe

The special file control services that CICS provide are data independence, exclusive control over resources over update, and file open and close. By data independence we mean that the program should be independent of the structure of the database or data access methods. CICS File control provides the application programmer with data independence, so that they do not have to be concerned with the data dependent parameters. The system programmer defines the File Control Table (FCT) to specify the characteristics of the files used by CICS and the application programmer codes the CICS Commands in his program. So the structure of the database and access methods are transparent to application developer.

If a task is updating a record, some other task must be prevented from the access of that record to preserve data integrity. This is called exclusive control during updates. CICS automatically gives exclusive control to the program or task, which is performing the data update. For an application to do a file access it must be open. The FCT defines the initial open/close status of the entire file. The application programmer can open or close a file using the CEMT command.


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