Chapter 5 - Logic
The formal foundation of the OWL language is a branch of knowledge representation and reasoning
called description logics. While this foundation is promising, there is a differnt approach to
representation and reasoning based on rules. Its main advantages are:
Rule engines exist and are quite powerful.
Rules are well known and used in mainstream IT, and is easier for users to learn.
Rule systems can be seen as an extension, or as an alternative to OWL. The first idea is driving
current research attempting to integrate description logics and rules, while maintaining somewhat
efficient reasoning support. The latter idea studies the use of RDF/S in conjunction with rules as
the basis of an alternative Web ontology language.
Apart from classical rule systems, it is interesting to consider systems that can deal with contradictory
conclusions. Such systems are interesting for modeling default inheritance and rules with exceptions. They
are also very useful for knowledge integration, where inconsitences can naturally occur when knowledge from
different sources is put together.