Data entry database: DEDB

DEDBs are designed to provide access to and efficient storage for large volumes of data. The primary requirement a DEDB satisfies is a high level of data availability.

DEDB characteristics

DEDBs are hierarchic databases that can have as many as 15 hierarchic levels, and as many as 127 segment types. They can contain both direct and sequential dependent segments. Because the sequential dependent segments are stored in chronological order as they are committed to the database, they are useful in journaling applications.

DEDBs support a subset of functions and options that are available for a HIDAM or HDAM database. For example, a DEDB does not support logically related segments or access with primary indexes. Access with secondary indexes is supported.

An overview of how DEDBs work

This topic contains Diagnosis, Modification, and Tuning information.

A DEDB can be partitioned into multiple areas, with each area containing a different collection of database records. The data in a DEDB area is stored in a VSAM data set. Root segments are stored in the root-addressable part of an area, with direct dependents stored close to the roots for fast access. Direct dependents that cannot be stored close to their roots are stored in the independent overflow portion of the area. Sequential dependents are stored in the sequential dependent portion at the end of the area so that they can be quickly inserted. Each area data set can have up to seven copies, making the data easily available to application programs.