Three-schema approach

It proposes three different views in systems development, with conceptual modelling being considered the key to achieving data integration.

From the user view, which will be referred to as the “external schema,” the definition of data is in the context of reports and screens designed to aid individuals in doing their specific jobs.

From the computer view, which will be referred to as the "internal schema", data is defined in terms of file structures for storage and retrieval.

Data was defined by the layout of physical records and processed sequentially in early information systems.

The need for flexibility, however, led to the introduction of Database Management Systems (DBMSs), which allow for random access of logically connected pieces of data.

Furthermore, most large companies have had to develop multiple databases which are often under the control of different DBMSs and still have the problems of redundancy and inconsistency.

Over the next twenty years, various groups attempted to define standards for the conceptual schema and its mappings to databases and programming languages.

The notion of a three-schema model was first introduced in 1975 by the ANSI/X3/SPARC three level architecture , which determined three levels to model data. [ 1 ]
Figure 1: Traditional View of Data [ 6 ]
Figure 2: Three schema approach [ 6 ]
Image of the six layers in the Zachman Framework .