Virtual Storage Access Method - IBM Mainframe

The CICS File Control Program (FCP) provides application programs with services to read, add, modify and delete records in a file. It also makes the application programs independent of the structure of the database, while manages exclusive control over the records in order to maintain the data integrity during record updates. CICS file control supports the Virtual Storage Access Method (VSAM) and Basic Direct Access Method (BDAM), but VSAM is the primary data access method under CICS. There are 3 types of VSAM files, all of which are supported under CICS. They are

  • VSAM/Key Sequenced Dataset (KSDS)
  • VSAM/Entry Sequenced Dataset (ESDS)
  • VSAM/Relative Record Dataset (RRDS)

A VSAM file used for CICS must have at least one record loaded to initialize the file, even if this single can be deleted later. Files are generally opened and closed when CICS is initialized and Shutdown respectively. Therefore, the programs need not open or close the files.

All CICS files must be defined in the File Control Table (FCT). Some of the details that is contained in FCT are dataset name, record size, permissible file access and update functions, etc. The FCT eliminates the need for the programmer to define those data-dependent variables in the INPUT-OUTPUT SECTION, SELECT statement, FD statement, JCL etc., thus giving data independence to the application programs. The file characteristics are defined to CICS in the FCT usually by the system programmer. So the application programmer can code application programs using the ClCS commands.

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