Abstract
Expert systems use sophisticated programs, often in conjunction with large but highly specific databases. A fifth-generation information system (5GIS) is like a “user-definable” expert system, in that it allows the user to enter a description of the universe of discourse and then conduct a conversation about this, all in a natural language. An information system for a given application may be viewed from at least four levels: conceptual, logical, internal, and external. The conceptual level is the most fundamental, portraying the application domain naturally in human concepts. The conceptual schema specifies the structure for all permitted states and transitions of the conceptual database. An external schema specifies the UoD design and the operations accessible to a particular user or group of users. This chapter provides an overview of how conceptual schemas may be implemented in relational database systems. Each database management system (DBMS) conforms to a logical data model, that is, network, hierarchic, or relational. If a relational DBMS is chosen for the implementation, the conceptual schema is mapped to a relational schema, or relational database schema. Various frameworks also exist for information system architecture.
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