Identification, genericity and consistency in object-oriented databases
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It is claimed that object-oriented databases overcome many of the limitations of the relational data model especially by generalizing the notion of object identification. A clear distinction between objects and values turns out to be essential for the object-oriented approach whereas the relational model is based exclusively on values. Since, however, value uniqueness within scopes is a quite natural constraint for a wide class of applications, identification by value is also of interest for object-oriented datamodels.
Hence, in this paper we concentrate on those classes where the extents are completely representable by values. We formalize some basic concepts of object-oriented databases and show that the finiteness of a database and the existence of finitely representable recursive types are sufficient to decide value-representability.
Another advantage of the relational approach is the existence of structurally determined canonical update operations. We show that this property can be carried over to object-oriented datamodels iff classes are value-representable. Moreover, in this case database consistency with respect to implicitly specified referential and inclusion constraints will be automatically preserved.
KeywordsRepresentation Type Uniqueness Constraint Identification Graph Object Identifier Explicit Constraint
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