Thinking on the Web: Berners-Lee, Gödel and Turing

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LOGIC, RULES, AND INFERENCE

OVERVIEW

The architecture of the Semantic Web is comprised of a series of layers that form a hierarchy of content and logic. The ontology layer defines knowledge about content, concepts, and relationships. Currently, the RDF Schema (RDFS) is recognized as an ontology language that provides classes, properties, sub/superclasses, range, and domain. However, RDFS has no localized range and domain constraints, no cardinality constraints, no provision for negation, and no transitive, inverse, or symmetrical properties. As a result, RDFS is unable to provide sufficient expressive power for machine processing on the Semantic Web.

To expand the expressive capabilities of RDFS, three versions of the Web Ontology Language (OWL) have been developed: OWL Full is the union of OWL syntax and RDF, but it is undecidable and therefore cannot provide complete reasoning support. OWL DL is a sublanguage of OWL Full that has efficient reasoning support, but is not fully compatible with RDF. OWL Lite is an “easier-to-implement” subset of OWL DL.

RDF and OWL DL are both consistent with predicate logic (also known as first-order logic (FOL)) and are used to enable Web knowledge representation. They provide a syntax that promotes their use on the Web where key information is carried in tags, delimiters of the material content. OWL DL and OWL Lite are simplifications of the OWL Full that are designed to enable the use of descriptive logic, which is a subset of predicate logic ...