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   Invited Talks

The limits and possibilities for combining Description Logics and Datalog

Riccardo Rosati, Universita di Roma


Description Logics are currently the most used formalisms for building ontologies, and have been proposed as standard languages for the specification of ontologies in the Semantic Web. The problem of adding rules to Description Logics is currently a hot research topic, due to the interest of Semantic Web applications towards the integration of rule-based systems with ontologies. Most of the approaches in this field concern the study of description logic knowledge bases augmented with rules expressed in Datalog and its nonmonotonic extensions. In this talk we present a set of computational results which identify, from the viewpoint of the expressive abilities of the two formalisms, minimal combinations of Description Logics and (nonmonotonic) Datalog in which reasoning is undecidable. Then, based on the above results, we briefly survey some recent proposals for overcoming such expressive limitations.

Rule-based intelligence in the Semantic Web -or- "I'll settle for a web that's just not so dumb!"

Dean Allemang, Top Quadrant


My keynote will give both a retrospective and prospective view of rules and the semantic web.

The role of rules in the semantic web has been controversial; in the few short years since the first publication of the Semantic Web stack, Rules have sometimes been given a central role, at other times a peripheral role, and sometimes left out completely. Why such variation for an technology with thirty years of background?

The reason for these differences of opinion stem from different goals for the inclusion of rules in the Semantic Web stack. At one extreme are the Description Logicians who see no need for a general-purpose programming language in the semantic web stack. At the other extreme are those who want to build a web infrastructure with the capacity for emergent intelligence.

Our experience with deploying semantic web solutions using OWL alongside rules suggests a moderate middle path; we don't need or even want our web infrastructure to exhibit intelligence; that's what our applications are for. We just need a consistent and coherent web of information to work from. Simply put, we just want our web infrastructure not to be so dumb. Armed with this understanding, I see the rules in the Semantic Web in a different light, and see a clear role of rules in the semantic web stack.

This keynote will illustrate these themes with experiences in the field.