This is part two of a series of three articles that will address conceptual, logical and physical models, object models and data model views. The goal of this series is to provide a clear vision of how all these elements relate to each other.
The ANSI three-schema architecture (that we have expanded here to four schemata) and John Zachman's information architecture provide a good basis for understanding the nature of data models.1,2 The ANSI architecture describes the external schema that represents the way a business owner views a business. Data models of this view tend to consist of terms for concrete things actually seen and manipulated by the business people. (This is the "business owner's view" in John Zachman's Architecture Framework.) The most important thing to capture in representing this view is the vocabulary. The conceptual schema represents the fundamental, underlying structure of the organization. The conceptual data model is inferred from multiple external business owners' views and is much more rigorous in its representation (the "architect's view").3 The internal schema is really two: the logical schema which represents data in terms appropriate to a particular data manipulation approach as usually expressed in a database management system or DBMS (the "designer's view") and the internal schema which is concerned with the physical characteristics of storage on a storage device ("builder's view").
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