O!-LOLA - Extending the Deductive Database System LOLA by Object-Oriented Logic Programming

نویسنده

Günther Specht

چکیده

This paper presents the declarative extension of the deductive database system LOLA to the object-oriented deductive database system O!-LOLA. The model used for O!-LOLA is \objects as theories", extended by state evolution. O!-LOLA combines logic programming and OO programming in two diierent w ays: First, methods are implemented as logic programs. These methods can be inherited, encapsulated and overloaded. Second, logic programs can be deened over classes, meta-classes, instances, attributes and values. Dynamic updates of attributes of objects and dynamic instantiations of classes are supported. O!-LOLA is implemented as a preprocessor. O!-LOLA programs are transformed into LOLA rules and facts, which are evaluated set-oriented and bottom-up, using xpoint s e m a n tics. Some object-oriented features concerning dynamic aspects are handled via built-in predicates in LOLA. We describe the applied theory, the system and the preprocessor, including an example of how methods are translated and we discuss dynamic updates of objects in O!-LOLA. The beneets of our system in contrast to others are: a single integrated language, clear semantics and a set-oriented evaluation. O!-LOLA uses xpoint semantics (not any procedural semantics like other systems) and still evaluates set-oriented (and not in a mixed manner like other systems). Thus, we can fully use all optimization techniques developed for deductive databases and gain a very eecient system. 1. Introduction. Within the last years the two main areas of research in extending database programming languages have been deduc-tive database languages and object-oriented database languages. Logic (or deductive) databases augment the relational model by Herbrand terms in

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