SHISAM databases

A simple HISAM (SHISAM) database is a HISAM database containing only one type of segment, a root segment.

SHISAM databases have the following restrictions:

• They have no dependent segments. Only root segments are allowed.
• They cannot have secondary indexes.
• They cannot have logical relationships.
• All segments are fixed length. They do not support variable length segments.
• Compression is not allowed.

The segment has no prefix, because no need exists for a segment code (there is only one segment type) or for a delete byte (deletes are done using a VSAM erase operation). SHISAM databases must be KSDSs; they are accessed through VSAM. Because SHISAM segments contain user data only (no IMS prefixes), they can be accessed by VSAM macros and DL/I calls. All the DL/I calls can be issued against SHISAM databases.

Since SHISAM segments have no prefix and SHISAM requires only one data set, it requires less space than a root-only HISAM, HIDAM, or PHIDAM database.

To select SHISAM, specify ACCESS=SHISAM on the DBD statement. To process a KSDS with fixed length records as an IMS database, define it as SHISAM.