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Deriving Relationships between Integrity Constraints for Schema Comparison.pdf

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Deriving Relationships between Integrity Constraints for Schema Comparison

Deriving Relationships between IntegrityConstraints for Schema ComparisonCan Turker and Gunter SaakeOtto-von-Guericke-Universitat MagdeburgInstitut fur Technische und Betriebliche InformationssystemePostfach 4120, D{39016 Magdeburg, Germanyftuerkerjsaakeg@iti.cs.uni-magdeburg.de To appear in: W. Litwin, T. Morzy and G. Vossen, editors, Second East-EuropeanSymposium on Advances in Databases and Information Systems (ADBIS98),September 8-11, 1998, Poznan, Poland, LNCS, Springer-Verlag, Berlin, 1998. Abstract. Schema comparison is essential for integrating dierentdatabase schemata. Since the semantics of a schema is also representedby its integrity constraints, they must be considered by a correct schemacomparison method. Especially the extensional relationships betweenclasses are determined by the relationship between the correspondingintegrity constraint sets. In this paper, we work out the relationships be-tween dierent types of integrity constraints. As a result, we present rulesfor comparing integrity constraint sets. These rules can be used after aschema conforming step, where naming, type and structural con icts aresolved, to exactly x the extensional relationship between object classes.1 IntroductionSchema integration [1] is one of the central issues in logically integrating databasesystems [6]. Schema integration aims at deriving an integrated schema which isa virtual view on all database classes to be integrated. Traditionally, all existingschema integration methods, e.g. [4, 7, 3, 2, 5], assume that the database designer{ as integrator { is an expert of the application domain who has complete know-ledge about the semantics of the schemata to be integrated. Thus, the databasedesigner should be able to exactly dene the extensional relationship betweentwo classes of dierent schemata in the schema comparison step. Obviously, thisis a very hard task for the database designer.A key point which is not regarded by the existing integration approaches isthe cor