HSAM databases

Hierarchical sequential access method (HSAM) databases use the sequential method of accessing data. All database records and all segments within each database record are physically adjacent in storage.

An HSAM database can be stored on tape or on a direct-access storage device. They are processed using either basic sequential access method (BSAM) or queued sequential access method (QSAM) as the operating system access method. Specify your access method on the PROCOPT= parameter in the PCB. If you specify PROCOPT=GS, QSAM is always used. If you specify PROCOPT=G, BSAM is used.

HSAM data sets are loaded with root segments in ascending key sequence (if keys exist for the root) and dependent segments in hierarchical sequence. You do not need to define a key field in root segments. You must, however, present segments to the load program in the order in which they must be loaded. HSAM data sets use a fixed-length, unblocked record format (RECFM=F), which means that the logical record length is the same as the physical block size.

HSAM databases can only be updated by rewriting them. Delete (DLET) and replace (REPL) calls are not allowed, and insert (ISRT) calls are only allowed when the database is being loaded. Although the field-level sensitivity option can be used with HSAM databases, the following options cannot be used with HSAM databases:

• Multiple data set groups
• Logical relationships
• Secondary indexing
• Variable-length segments
• Segment edit/compression exit routine
• Data Capture exit routines
• Asynchronous data capture
• Logging, recovery, or reorganization

Multiple positioning and multiple PCBs cannot be used in HSAM databases.