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

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 t he data may be facilitated by providing semantic views over the repositorie s that hide all the technical and organizative details associated with them . In this paper we present the definition of the mapping relation that perm its one to relate data elements of the semantic views and those of the unde rlying data repositories. We define the syntax and the semantics of the map ping. From the syntactic point of view, mapping expressions are tuples whos e main components are relational algebra expressions. From the semantic poi nt of view, the notions of well formed mapping relation and the extension d efined by that mapping are introduced. Moreover, we demonstrate the complet eness property Of the mapping relation in the sense that it allows for answ ers to all queries formulated over the semantic view using the data stored in the data repositories. Copyright (C) 1999 Published by Elsevier Science Ltd.