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Concept
Three-schema approach
Résumé
The three-schema approach, or three-schema concept, in software engineering is an approach to building information systems and systems information management that originated in the 1970s. It proposes three different views in systems development, with conceptual modelling being considered the key to achieving data integration.
The three-schema approach provides for three types of schemas with schema techniques based on formal language descriptions:
External schema for user views
Conceptual schema integrates external schemata
Internal schema that defines physical storage structures
At the center, the conceptual schema defines the ontology of the concepts as the users think of them and talk about them. The physical schema according to Sowa (2004) "describes the internal formats of the data stored in the database, and the external schema defines the view of the data presented to the application programs." The framework attempted to permit multiple data models to be used for external schemata.
Over the years, the skill and interest in building information systems has grown tremendously. However, for the most part, the traditional approach to building systems has only focused on defining data from two distinct views, the "user view" and the "computer view". 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. The required structure of data from a usage view changes with the business environment and the individual preferences of the user. 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. The required structure of data for computer storage depends upon the specific computer technology employed and the need for efficient processing of data.
These two traditional views of data have been defined by analysts over the years on an application by application basis as specific business needs were addressed, see Figure 1.
Source officielle
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