2.5. Summary
An information system for a given application may be viewed from at least four levels: conceptual, logical, physical, and external. At each level the formal model or knowledge base comprises a schema that describes the structure or design of the UoD and a database that is populated with the fact instances. Each schema determines what states and transitions are permitted for its database(s).
The conceptual schema does this in terms of simple, human-oriented concepts. The logical schema groups information into structures supported by the generic logical architecture (e.g., relational). The physical schema specifies the physical storage and efficient access structures (e.g., indexes) for the specific DBMS or platform being used to ...
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