Michael Kifer
Rule Interchange Format: The Framework
Slides (PPT)
The Rule Interchange Format (RIF) is a W3C activity aimed at developing a
Web standard for exchanging rules. The need for rule-based information
processing on the Semantic Web has been felt ever since RDF was introduced
in the late 90's. As ontology development picked up pace this decade and
the limitations of OWL became more apparent, rules were firmly put back on
the agenda. RIF is therefore a major opportunity for the introduction of
rule based technologies into the main stream of knowledge representation
and information processing.
Despite its humble name, RIF is not just a format and is not primarily
about syntax. It is an extensible framework for rule-based languages,
called RIF dialects, which includes precise and formal specification of
the syntax, semantics, and XML serialization of the dialects. In this
talk we will discuss the main principles behind RIF, introduce the RIF
extensibility framework, and present the Basic Logic Dialect---the only
fully developed RIF dialect so far. We will also discuss the opportunities
for community involvement in furthering this standard.
Boris Motik
Semantics and Reasoning Algorithms for a Faithful Integration of Description Logics and Rules
Slides (PPT)
Description logics (DLs) and rule-based systems are two prominent families of knowledge representation formalisms. While DLs are
focused on describing and reasoning about conceptual knowledge, rules are focused on answering queries about facts in the knowledge
base. So far, research on DLs has been largely isolated from the research on rules. With the advent of the Semantic Web, however, it
became apparent that neither formalism alone can cover all the practical use cases. The integration between DLs and rules, however,
is technically challenging due to significant differences in the underlying semantic assumptions. In particular, DLs are based on
standard first-order semantics and open-world assumption, whereas rules typically employ closed-world semantics based on a variant
of circumscription.
In my talk, I shall present an overview of the benefits of integrating DLs and rules in a coherent semantic framework, and shall
discuss the main challenges in achieving a tight integration. I shall present an overview of the approaches currently discussed in
literature. Finally, I shall present in more detail the approach that is based on the nonmonotonic logic MKNF by Lifschitz. This
approach is tight in the sense that DLs and rules are given a common model-theoretic semantics. Furthermore, it is faithful in the
sense that it is compatible with the original semantics of both DLs and rules. Finally, it is expressive and can naturally capture
many of the existing proposals. I shall discuss the definitions of the semantics of the hybrid formalism, present a decision
procedure for a particular decidable fragment, and discuss the complexity bounds of reasoning.