Web Ontology Language (OWL) is built on top of RDF and RDF-S but has an increased vocabulary for handling classes and their properties. Some examples include cardinality (minimum and maximum occurrences of a property), class intersection and union, and equivalence and subset relationships. For instance, using OWL we can say that a SnakeRobot is a subclass of Robot:
<owl:Class rdf:ID="SnakeRobot"> <rdfs:subClassOf rdf:resource="#Robot" /> </owl:Class>
Or that a SnakeRobot looksLike a snake:
<owl:Class rdf:ID="SnakeRobot"> <owl:Restriction> <owl:onProperty rdf:resource="#looksLike" /> <owl:someValuesFrom rdf:resource="http://xmlns.com/wordnet/1.6/Snake"/> </owl:Restriction> </owl:intersectionOf> </owl:Class>
A W3C recommendation since February 2004, W3C's Semantic Web Interest Group has labeled OWL as one of the "principle technologies of the Semantic Web." As such, OWL can be found in many projects including the University of Maryland's Mindswap that utilizes OWL for many of its different projects. The First International Semantic Web Services Symposium website and other websites include semantic annotations in OWL. Several OWL reasoners are available as well, and more OWL implementations may be found on W3C's website.
OWL is similar to its predecessor, DAML+OIL.
- W3C's OWL W3C's OWL site with good lists of tools, projects, and specifications
- W3C's OWL Overview An overview of the features available in OWL
- OWL on Wikipedia
- W3C's OWL Guide A great W3C OWL guide that explains ontology creation from beginning to end. Also contains a list of links of background basics and OWL history.
- W3C OWL Language Reference For when you're looking for a specific term
- OWL Glossary
- W3C's Semantic Web Interest Group
- UMD's Mindswap
- OWL Implementations