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IMS-DL/I: A Hierarchical Database

An IMS-DL/I database is a large, centralized collection of information comprising one or more physical files that can be accessed by the SAS/ACCESS interface to IMS-DL/I. An IMS-DL/I database is a hierarchical database: one where information is structured in records that are subdivided into a hierarchy of related segments.

You can think of a record as a root segment and all of its dependent segments. Segments are further subdivided into fields. The data in any record relate to one entity. Ideally, information in the database records is subdivided into segments and fields on some logical basis, either by the inherent structure of the data or by consideration of the uses to which the data will be put.

The term hierarchical implies that there are levels of data. You can think of a hierarchical database as one that starts at the top with general information about the item, individual, or case. As you progress from level to level down through the hierarchy, more and more information related to the general information at the top level is given. Each level in the hierarchy has one or more segments.

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