Mapping among knowledge bases and data repositories: Precise definition of its syntax and semantics

摘要

Nowadays there is an explosion of data repositories available in the Global Information System. In this context, users meet with the problems related to the heterogeneity and distribution of the data repositories. Access to the data may be facilitated by providing semantic views over the repositories that hide all the technical and organizative details associated with them. In this paper we present the definition of the mapping relation that permits one to relate data elements of the semantic views and those of the underlying data repositories. We define the syntax and the semantics of the mapping. From the syntactic point of view, mapping expressions are tuples whose main components are relational algebra expressions. From the semantic point of view, the notions of well formed mapping relation and the extension defined by that mapping are introduced. Moreover, we demonstrate the completeness property of the mapping relation in the sense that it allows for answers to all queries formulated over the semantic view using the data stored in the data repositories.