Indirect Data Set Reference

Enhanced Definition

In the z/OS environment, an **indirect data set reference** occurs when a `DD` statement in JCL specifies a data set name that does not directly point to the physical data set but instead refers to an entry in the system catalog or a Generation Data Group (GDG) base, which then resolves to the actual data set. This mechanism provides a layer of abstraction, allowing applications to access data without needing to know the specific, current physical name or generation.

Key Characteristics

- Abstraction Layer: Provides a level of indirection between the logical data set name used in JCL and the physical data set name or its specific generation.
- Dynamic Resolution: The z/OS operating system resolves the actual physical data set name at execution time by consulting the system catalog or the GDG index.
- Common for GDGs: It is the standard and most prevalent method for referencing specific generations within a Generation Data Group (GDG), using a relative generation number (e.g., (0) for the current, (-1) for the previous).
- VSAM Cluster Access: When referencing a VSAM (Virtual Storage Access Method) cluster, the cluster name itself acts as an indirect reference to its underlying data and index components.
- Flexibility: Allows applications and batch jobs to remain unchanged while the underlying physical data sets (or their generations) are swapped, updated