Mapping external views to a common data model

摘要

In the context of a multilevel database management system architecture, the problem arises of translating, or mapping, operations at the user's representation level (the External Schema) into operations at the system's common logical level (the Conceptual Schema).In order to support different structured user's data models, the need for an unstructured, view-independent and yet carefully defined data model at the Conceptual Schema level is recognized.In this paper a binary model for the Conceptual Schema is illustrated through the specification of a set of primitives, and the elements of a language for the definition of a binary Schema and of the corresponding operations are given.Procedures are then illustrated for translating external into conceptual operations through exploitation of the primitives of the binary model. Two types of mapping specifications are illustrated: the operational mapping, in which the translation is explicitly defined, and the structural mapping, in which only the structural correspondences between elements of the External and the Conceptual Schema are defined. The automatic mapping between n-ary relational views and the binary Conceptual Schema is finally discussed.