Identification through catalog

A catalog contains pointers to previously cataloged data sets. The system uses these pointers to locate data sets when a DD statement requests an old data set without UNIT or VOLUME parameters. For example: 
   //ddname  DD  DSNAME=dsname,DISP=OLD

Allocation and unallocation of catalog volume

When the DSNAME parameter requests a cataloged data set, the system mounts the catalog volume, if it is not already mounted. From the catalog, the system obtains the pointer to the requested data set.

The operating system no longer supports DD statements with the names of JOBCAT or STEPCAT. You can use aliases to direct catalog requests to the appropriate catalog. For more information see z/OS DFSMS Access Method Services Commands.

To locate a data set, the system searches catalogs in the following order:
  1. The catalog pointed to by an alias in the system master catalog that matches the first one to four qualifiers, if any, of the data set name.
  2. The master catalog.
Parent topic: Data set resources - identification