Catalog
The system's index of where datasets live, so you can refer to a dataset by name without knowing which disk it is on.
Also written ICF catalog, master catalog, user catalog
The catalog records which volume each dataset resides on. Because of it, you name a dataset and the system finds it; without it you would have to state the disk volume every time.
The structure has two levels. A master catalog is the entry point for the system, and it points to user catalogs that hold the actual entries. Which user catalog a dataset belongs to is decided by an alias on its high-level qualifier, which is another reason the first qualifier of a name matters so much.
A dataset described by the catalog is catalogued; one that exists on a volume without an entry is uncatalogued, and you have to specify its volume to reach it. Uncatalogued datasets are rare in normal work and usually a sign something went wrong.
Catalog entries are created and removed automatically as JCL creates and deletes datasets. They can also be managed directly with IDCAMS, which is how you list what a catalog knows about a dataset and repair entries that have got out of step with reality.
Related terms
- Dataset nameThe full name of a dataset, written as dot-separated qualifiers of up to eight characters each.
- High-level qualifierThe first part of a dataset name, which usually identifies the owner and drives how security and storage rules apply.
- VolumeA single unit of disk storage with a six-character label, on which datasets are placed.
- IDCAMSThe utility used to create, list, copy and delete datasets, and the standard tool for anything involving VSAM.
- DispositionThe DISP parameter, which says whether a dataset already exists, and what to do with it when the step ends normally or fails.