Data entry databases (DEDBs)

A DEDB contains a root segment and as many as 127 dependent segment types. One of these can be a sequential dependent; the other 126 are direct dependents. Sequential dependent segments are stored in chronological order. Direct dependent segments are stored hierarchically.

Restriction: IMS does not support inserting SDEP segments into the same DEDB area from multiple distributed IMS PSTs or UORs, as a global UOR, instanced from a non-IMS resource manager.

This restriction applies to ODBA users, ODBM users, CCTL DRA users such as CICS, and Db2 stored procedures that access IMS using ODBA.

DEDBs can provide high data availability. Each DEDB can be partitioned, or divided into multiple areas. Each area contains a different collection of database records. In addition, you can make as many as seven copies of each area data set. If an error exists in one copy of an area, application programs continue to access the data by using another copy of that area. Use of the copy of an area is transparent to the application program. When an error occurs to data in a DEDB, IMS does not stop the database. IMS makes the data in error unavailable but continues to schedule and process application programs. Programs that do not need the data in error are unaffected.

DEDBs can be shared among application programs in separate IMS systems. Sharing DEDBs is virtually the same as sharing full-function databases, and most of the same rules apply. IMS systems can share DEDBs at the area level (instead of at the database level as with full-function databases), or at the block level.

Restriction: IMS does not support inserting SDEP segments into the same DEDB area from multiple distributed IMS PST or UORs as a global UR, instanced from a non-IMS resource manager.
This restriction applies to users of:
  • ODBA
  • ODBM
  • CCTL DR, such as CICS
  • Db2 stored procedures that access IMS using ODBA

Related reading: For more information on DEDB data sharing, see the explanation of administering IMS systems that share data in IMS Version 15.3 System Administration.