Use of Native VSAM Data Sets

Database Access Commands › Navigational DML › Use of Native VSAM Data Sets

Use of Native VSAM Data Sets

Native VSAM data sets can be defined in an CA IDMS/DB database schema and accessed by CA ADS database commands as if they were standard database files. CA IDMS/DB supports all three types of VSAM data sets: key sequenced (KSDS), entry sequenced (ESDS), and relative record (RRDS).

Existing VSAM data structures are accessed by equating them to CA IDMS/DB structures in the schema. The dialog issues standard process command statements for the equivalent CA IDMS/DB structures and the DBMS converts these statements to native VSAM access requests for the appropriate VSAM structures.

When a dialog's subschema includes records in a native VSAM file, process code for the dialog is affected in the following ways:

The set status condition cannot be used with sets defined for native VSAM data records.
Some database commands are affected, as listed below.

The following table lists considerations that apply to specific database commands when using native VSAM data sets.

Database Commands and Native VSAM Data Sets

Command	Consideration
ACCEPT DB-KEY RELATIVE TO CURRENCY	Next, prior, and owner currency cannot be requested for sets defined for native VSAM records.
CONNECT	The CONNECT command is not allowed because all sets in native VSAM data sets must be defined as mandatory automatic.
DISCONNECT	The DISCONNECT command is not allowed because all sets in native VSAM data sets must be defined as mandatory automatic.
ERASE	ERASE record-name is the only form of the ERASE command that is valid for use with native VSAM data sets. No form of the ERASE command is permitted against records contained in an ESDS.
FIND/OBTAIN DB-KEY	The FIND/OBTAIN DB-KEY command cannot be used to access records in a native VSAM KSDS because the database key does not necessarily remain static in a KSDS.
FIND/OBTAIN OWNER	The FIND/OBTAIN OWNER command is not allowed because owner records are not defined in native VSAM data sets.
FIND/OBTAIN WITHIN SET/AREA	When an end-of-set or end-of-area condition occurs, all currencies remain unchanged. The FIRST, LAST, and sequence-vn WITHIN AREA options cannot be used to access spanned data records in a native VSAM data set.
MODIFY	The length of a record in an ESDS file cannot be changed even if the record is variable length. The prime key for a KSDS cannot be modified.
STORE	If the object record is to be stored in a native VSAM RRDS, the DIRECT-DBKEY field must be initialized with the relative record number of the record being stored.

More information:

Conditional Expressions