Integrity Constraints Representation in Object-Oriented Databases

This paper presents a Data Definition Language (DDL), called TQL, based on an Object-Oriented data model characterized by the possibility of expressing integrity constraints in the schema of the database. The work originates from the need to enrich the amount of knowledge represented, declaratively, in the database schema and processed by the Database Management System (DBMS). The proposed approach allows the reduction of the amount of code in methods. However, by increasing the power of the DDL, the possibility of introducing errors in the schema also increases. Therefore, rich data models require enhanced checking facilities in order to support the design phase. In the paper, after having formally presented the language TQL, the notions of satisfiability and correctness of a TQL schema, which are strictly related to the notion of a legal database state, are introduced. These issues are presented using a formal approach based on a denotational semantics which concerns both the structural part of the schema and the integrity constraints.