Introduction to the New Mainframe: z/VSE Basics

146 Introduction to the New Mainframe: z/VSE Basics

򐂰 Entry Sequence Data Set (ESDS)

This form of VSAM keeps records in sequential order. Records can be

accessed sequentially.

򐂰 Relative Record Data Set (RRDS)

This VSAM format allows retrieval of records by number: record 1, record 2,

and so forth. This provides random access and assumes that the application

program has a way to derive the desired record numbers.

򐂰 Variable-length Relative-record Data Set (VRDS)

This is the same as a Relative Record Data Set (RRDS), however, with the

ability to handle variable length records.

5.5.1 What is a VSAM catalog?

VSAM uses a central file called a catalog to perform space and file management.

The catalog itself is a VSAM file. It is self-describing and contains ...