Information Management System (IMS) is a general term for software designed to facilitate the storage, organization, and retrieval of information.

Unlike DB2 (IBM’s relational database software), an IMS database uses segments, or data blocks, as building blocks of the hierarchical model. Within each segment are multiple data pieces, which are known as fields. At the top of the hierarchy, the segment is known as the root segment. Segments of a specific segment are known as child segments. The child segment order represents the order in which each entry is entered in a database.

Hierarchical IMS databases generally come in three forms:

• Full function database: Derived from the Data Language Interface (DL/I), this database form may have more than one single access method. Overflow Sequential Access Method (OSAM) or Virtual Storage Access Method (VSAM) may be used to store and access database fields.

• Fast path database: Designed to facilitate an optimum transaction rate. Examples are data entry databases (DEDB) and main storage databases (MSDB).

• High availability large databases (HALDB): Handles large volumes of data and provides reliable availability for each piece of data in the database.