Schema Definition

Native VSAM Considerations › CA IDMS/DB Native VSAM Definitions › Schema Definition

Schema Definition

The schema establishes the correspondences between the logical characteristics of the native VSAM file and CA IDMS/DB, as follows:

A File

A CA IDMS file represents a VSAM cluster or path:

A KSDS with a prime index or alternate indexes or both
An ESDS with or without alternate indexes
An RRDS

An area represents a KSDS, ESDS, or RRDS data component. You map one area to each VSAM file; each area must have a unique page range. The page range is a function of the VSAM data set structure. For more information about how to determine the page range, see "AREA statements" in Physical Database DDL Statements.

A Schema Record

A schema record represents a VSAM data record:

All VSAM data records can be represented as a record with a location mode of VSAM
A KSDS with a prime index or alternate indexes and an ESDS with an alternate index can be represented as a CALC record

A Schema Set

A schema set represents the index of a VSAM data set and related records. These sets are sorted and maintained through the following types of native VSAM data set structures:

A KSDS with a prime or alternate index
An ESDS with an alternate index

You define sets with alternate indexes in the schema to allow record occurrences with duplicate sort keys. These record occurrences are retrieved in the order in which the records were stored, regardless of the order in which the set is searched. For sorted sets that do not allow duplicate sort keys, you can use any index to maintain the set.

Native VSAM sets allow you to code application programs that:

Access a specific record directly by sort key
Access records by generic sort key
Process the native VSAM file in sort-key sequence from the start of the file or from a specified starting point.

Relationships Between VSAM and CA IDMS/DB Structures

The schema, AREA, RECORD, SET, and SET statements, and the segment statements needed to represent native VSAM structures are listed in the following table.

VSAM Structure	CA IDMS/DB Structure	DDL Statement
KSDS ESDS RRDS PATH	File	CREATE FILE segment.file-name
Data component: KSDS, ESDS, RRDS	Area	Schema definition: ADD AREA NAME IS area-name ... Segment definition: CREATE AREA segment.area-name ...
VSAM data record	Record	ADD RECORD NAME IS record-name LOCATION MODE IS VSAM VSAM TYPE IS type WITHIN AREA area-name.
VSAM data record: KSDS with prime or alternate index ESDS alternate index	CALC record	ADD RECORD NAME IS record-name LOCATION MODE IS VSAM CALC USING calc-element-name DUPLICATES ARE duplicates-option VSAM TYPE IS type WITHIN AREA area-name.
KSDS prime or alternate index ESDS alternate index	Set (sorted by prime or alternate key)	ADD SET NAME IS set-name MODE IS VSAM INCLUDE MEMBER IS record-name MANDATORY AUTOMATIC ASCENDING KEY IS sort-key-name.