Modelling Semantic Integrity Constraints in Object-Oriented Database Schemas

Recent years have witnessed a continuous evolution of database models towards richer and more expressive paradigms. Along the line of enriching the modeling capabilities, Object-Oriented databases (OODBs) have been introduced. In this paper, we propose a further enhancement to OODB models aiming at enriching the database schema by explicitly declaring semantic integrity constraints therein. In the paper we present an Object-Oriented data definition language, referred to as TQL. It allows the construction of an OODB schema using the well-known data structuring mechanisms, such as NF2 attributes, complex types, and multiple inheritance in class (type) hierarchies. In addition, TQL allows the further enrichment of the schema by expressing explicit integrity constraints. The proposal includes the definition of the formal semantics of TQL, according to a denotational approach, and the notion of correctness of schemas, with particular emphasis on the legality of ISA hierarchies. The proposed language is the basis of the prototype MOSAICO, an environment for the design and rapid prototyping of OODB applications developed at IASI.