Formalization of an IS-A based extended nested relation data model

摘要

Complex objects have values that are made up of components that can themselves be complex objects. These components are often intricately interrelated and can be portrayed as aggregation, association, and IS-A relationships. Traditional nested relations, while capable of supporting the aggregation and association semantics of complex objects, do not have any mechanism to support IS-A semantics. In this paper, we present a formalism to extend the nested relational model to include mechanisms to support the IS-A semantics associated with complex objects. The extension is achieved by the introduction of reference and discriminant attributes in the nested relational data model. The concept of a Semantic Normal Form (SNF) is also presented to ensure the elimination of uncontrolled redundancy in such nested relations. An algorithm that creates an extended nested relational scheme in SNF from an existing complex object scheme is also presented.