Database versioning

When database versioning and the IMS™ catalog are enabled in an IMS system, you can maintain multiple different versions of a database. Application programs can access the older versions of the database without being changed, while the newer versions of the database can be changed to support new application program requirements.

Database versioning overview
To create a new version of a database, database versioning must be enabled by specifying DBVERSION=Y in the DFSDFxxx PROCLIB member.
IMS catalog support for database versioning
The IMS catalog is required for database versioning.
Database modifications supported by database versioning
When you maintain multiple versions of a database, you can make only certain structural changes to the new versions of the database.
Database versioning, existing free space, and new fields
In the IMS definition of a segment, any bytes in the length of the segment that are not used by the fields that are defined in the segment are considered free space.
System default for database versioning
When an application program does not specify a specific version of a versioned database, by default IMS returns data to the application program by using the version of the database definition (DBD) that is currently active in the IMS catalog. You can change the default so that IMS returns data by using version 0 of the DBD instead.
Implementing database versioning
To maintain and access multiple versions of a database, you must enable database versioning, define the new version of the database, and generate the necessary DBD, PSB, and ACB members.
Logical relationships, secondary indexes, and database versioning
IMS database versioning supports both databases that have logical relationships and databases that have secondary indexes, as long as the segments that are involved in the relationship between the two databases, or that are paired with another segment in the same database, do not change in new versions of the DBD.

Parent topic: Database types and functions