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Thea

Thea is an Prolog library that provides complete support for querying and processing OWL2 ontologies directly from within Prolog programs.
Thea uses an SWI-Prolog’’s RDF library for parsing and serializing ontologies, but the core model is independent of RDF and is based on the OWL2 functional style syntax, allowing direct manipulation of ontology axioms through the Prolog database rather than indirectly via RDF triples.
While previous versions of Thea (up until 0.5.5) provided a small number of predicates to support the basic OWL entities – classes, properties and individuals, Thea2 was redesigned to support OWL2 following precisely its structural syntax specification: every axiom in the ontology would correspond on a one-to-one basis with facts in the prolog database. This allows querying the Ontology by simply query the prolog database using goals with variables as arguments.
Thea has support from the Semantic Web Rule Language (SWRL). SWRL antecedent-consequent rules are represented in the prolog database as facts using a two-argument implies/2 predicate, rather than directly as prolog rules. Thea also offers additional capabilities including a bridge to the java OWL API and translation of ontologies to Description Logic programs.