Hierarchical databases
The hierarchical model of data formed the basis for a number of early database management systems, the most prominent being IBM’s Information Management System (IMS). IMS was first released in 1968 and is still in use today with many legacy mainframe-hosted applications used for accounting and inventory control.
Figure B.3 shows an example of a schema diagram for a hierarchical database. The schema in Figure B.3 has only one hierarchy, but there could be many hierarchies in a single database. Each hierarchy comprises a number of record types, with each record type comprising a number of field types. Each hierarchy has a root record type. In Figure B.3 the root is the DEPARTMENT
FIGURE B.1 Conceptual data model
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