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IMS Data Entry Database

A data entry database is a more conventional type of database than an MSDB. It is structured in a similar manner to an HDAM database and is maintained in direct access storage rather than in main storage. However the characteristics of a data entry database make it well suited for high-performance applications that must provide very rapid response times. DEDB is best suited for storing databases that use a simple hierarchical structures.

Although a DEDB behaves to the application program a similar manner to an HDAM data, its physical structure is quite different. In a conventional HDAM database, the entire logical data base structure is spread across the whole database. If multiple data sets are used, the structure is broken up on a segment basis, and parts of each data base record may be contained in multiple data sets.

In DEDB, multiple data sets can be used, with each data set designated as an area. Each area contains segment occurrences of all types, and all segment occurrences that make up a given data base record are always stored in the same physical area. The area approach makes it possible for the DBA to implement very large data bases. Each area is independent of all other areas. If a failure occurs in one area, it can be taken out of service without affecting access to segment occurrences in the other areas.

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