A HIGH-ORDER LOGIC FOR OBJECT-ORIENTED LOGIC PROGRAMMING

Abstract

Deductive and object-oriented databases are two important extensions of the traditional database technology. Deductive databases extend the expressive power of traditional databases by means of recursion and declarative querying. Object-oriented databases extend the data modelling power of traditional databases by means of object identity, complex objects, classes, class hierarchy and inheritance. However both extensions have short-comings. Deductive databases lack powerful data modelling mechanisms while object-oriented databases lack logical semantics and declarative query language. Therefore, by combining the two approaches together, the respective shortcomings can be eliminated mid the advantages of both approaches reaped as well. There had been many other attempts which sought to integrate these two paradigms and many differ in their approaches. Some followed the evolutionary approach by extending the object-oriented database to incorporate the desired properties of the deductive databases or vice versa. Others adopted the revolutionary approach by building new logical theories to encompass the deductive object-oriented features. We will examine the systems already implemented and make comparison. From which, we will propose our own deductive object-oriented database: D02. The proposed database system will feature the following properties: • use of key value instead of object identity for object identification. • a powerful declarative language which incorporates object-oriented features: - referencing attributes by names - referencing inherited attributes directly from the subclass - supports method implementation - supports aggregation - supports recursion in rule declaration • an analytical approach to resolving (multiple) inheritance conflict within the ISA hierarchy • a more natural and powerful interpretation of negation using "not" predicates which allows for nested not predicates • a simple approach to extend the relational database to incorporate D00D features Our proposed approach is unique in that it allows any relational database to easily incorporate the desirable features of the two paradigms over it. We also examine the strength of D02 and highlight what separates it from the other deductive object-oriented database systems in this thesis. Finally, we will also discuss the possible extensions and development trends in the related fields of deductive object-oriented databases.