Defining user files

This section tells you how to define user files and how to access VSAM data sets, BDAM data sets, data tables, and coupling facility data tables.

About this task

CICS® application programs process files, which, to CICS, are logical views of a physical data set or data table. For data tables, the file provides a view of the data table, which resides either in data space storage or in a coupling facility structure. Except in the case of coupling facility data tables, for which an underlying physical data set is optional, a data table is also associated with a source data set from which the table is loaded. For non-data-table files, the file provides a view of the data set.

A file is identified to CICS by a file name of up to eight characters, and there can be many files defined to CICS that refer to the same physical data set or data table. This has the following effect, depending on the type of object the file is defining:
  • For non data table files, if more than one file refers to the same data set, each file refers to the same physical data.
  • For user-maintained data tables, if more than one file refers to the same data set, each file represents a view of a unique data table.
  • For CICS-maintained data tables, if more than one file refers to the same data set, only one can be defined as a CMT. The other files access data from the CMT created by the CMT file definition.
  • For coupling facility data tables, if more than one file refers to the same data set, each file represents a view of a unique coupling facility data table in a CFDT pool (unless each file specifies the same tablename and poolname, in which case each they provide a separate view of the same table.
A data set, identified by a data set name (DSNAME) of up to 44 characters, is a collection of data held on disk. CICS file control processes only VSAM or BDAM data. Any data sets referred to by CICS files must be created and cataloged, so that they are known to MVS™ before any CICS job refers to them. Also, the data sets are usually initialized by being preloaded with at least some data before being used by CICS transactions.

You can use CICS-maintained or user-maintained data tables to improve the performance and function of CICS regions using files that refer to VSAM data sets. Data tables offer a method of constructing, maintaining, and gaining rapid access to data records contained in tables held in data space storage, above 16MB. Each data table is associated with a VSAM KSDS, known as its source data set. For more information about data tables, see Defining data sets with multiple extents and volumes.

You can use coupling facility data tables to share data across a sysplex, using the CICS file control API, subject to some restrictions, such as a 16 byte key length.

You can use RLS access mode to share VSAM data sets between CICS application-owning regions throughout a sysplex. See VSAM record-level sharing (RLS) for further information.

Each of the above methods is discussed under the following topics: