6
WEB ONTOLOGY LANGUAGE (OWL)
OVERVIEW
Although XML Schema is sufficient to enable the exchange of data between parties who have agreed to the definitions beforehand, the lack of semantics prevents machines using this technology from reliably performing the task of data exchange when new XML vocabularies are introduced.1 In addition, the expressive power of RDF and RDF Schema (RDFS) is inherently limited because RDF is restricted to binary ground predicates and RDF Schema is restricted to a subclass hierarchy and a property hierarchy with domain and range definitions.2
In order for machines to perform automatic reasoning on Web documents, the language that machines use will need to go well beyond the basic semantics of XML Schema and RDF Schema.3 They will require a more expressive and reasoning ontology language, as a result, the W3C has defined Web Ontology Language (called OWL).
OWL enhances RDF with more vocabulary for describing properties and classes, including relations between classes (e.g., disjointedness), cardinality (e.g., “exactly one”), equality, richer typing of properties, characteristics of properties (e.g., symmetry), and enumerated classes.4
In this chapter, we first describe the requirements for OWL and its relationship with RDF Schema. Then we introduce Web Ontology Language and each of the three OWL versions currently available: Lite, DL, and Full. Some comparisons of OWL and RDFS are made and several illustrative examples are included.
ONTOLOGY LANGUAGE
Get Thinking on the Web: Berners-Lee, Gödel and Turing now with the O’Reilly learning platform.
O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.
