Allocating and Formatting Files › Considerations for Native VSAM Files

Considerations for Native VSAM Files

About Native VSAM Files

A native VSAM file is a file that is already defined to VSAM and contains VSAM records. Even though a native VSAM file is not structured as a CA IDMS database file, users can gain access to it using CA IDMS/DB DML. To access data in native VSAM data sets, CA IDMS/DB converts DML statements issued by an application program into record-level (not control-interval) VSAM requests and passes control to VSAM. A CA IDMS/DB local run unit or the central version appears to VSAM as a single application that:

1. Opens VSAM data clusters
2. Activates VSAM paths using local-shared resources (LSR) or non-shared resources (NSR)
3. Accesses data records
4. Closes the clusters and paths

Native VSAM Files Contain Data

CA IDMS/DB can access native VSAM files only if they contain at least one record; that is, the files cannot be empty. This also implies that empty native VSAM files cannot be loaded using CA IDMS/DB services.

Defining Native VSAM to CA IDMS

Before an existing VSAM file can be accessed using CA IDMS/DB DML statements, both a logical and physical description must be provided using non-SQL schema and physical DDL statements.

Note: For more information about defining native VSAM files, see Appendix D, "Native VSAM Considerations".