CA IDMS/DB Schema and VSAM File Correspondences › Key-Sequenced Data Set

Key-Sequenced Data Set

In VSAM, a key-sequenced data set (KSDS) contains records that are indexed by a prime key. When a KSDS is initially loaded, the physical sequence of the records may match the logical key sequence. After updates are made, the physical sequence and logical key sequence may or may not be in sync with each other.

The following rules apply to a VSAM KSDS:

• The prime key must be unique (duplicates are not allowed).
• The prime key must reside at a fixed displacement in the record-key field, even if the records are of variable length.