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Semantic and Schematic Similarities between Objects in Databases A Context based approach

In a multidatabase system schematic con icts between two objects are usually of interest only when the objects have some semantic similarity In this paper we try to reconcile the schematic and semantic perspectives We propose the concept of semantic proximity which is essentially an abstraction mapping between the domains of the two objects associated with the context of comparison The need for making explicit the meaning and use of an object provides the motivation for explicit representation of the semantic fulcrum i e the context of comparison A partial representation of context as a collection of contextual coordinates and their values is proposed The semantics of the speci city relationship between two contexts is de ned The contexts are organized as a meet semi lattice Associated operations like the greatest lower bound glb of two contexts and other operations are also de ned These operations along with the information on the type of abstractions used to relate two object classes form the basis of a semantic taxonomy The schematic and data con icts between object classes are enumerated and classi ed We then try to achieve the reconcilia tion of the semantic and schematic perspectives by discussing possible semantic similarities between two object classes that have various types of schematic and data con icts We introduce a uniform formalism called schema correspondences to represent structural similarities between the object classes At the semantic level the intensional description of the object classes in a database is provided by the context expressed in a description logic like language The schema correspondences use a modi ed object algebra to store mappings from the semantic level to the actual data organization in the databases and are associated with the respective contexts We again try to achieve the reconciliation of the semantic and schematic perspectives by modeling the schema correspondences as the projection of semantic proximity with respect to wrt context Changes in the context lead to changes in the schema correspondences An algebra to model these is also presented and explained with the help of illustrative examples