OWL inference engine using XSLT and JESS

 This page contains source code and instructions to load OWL ontologies and annotations into a JESS knowledge base. Using JESS, an open-source Java-based inference engine, one can infer new knowledge and solve queries. In the following we suppose that you are familiar with:

• JAVA - you should have JAVA 1.4 correctly installed;
• XSLT 1.0;
• JESS 6 -you should have JESS 6 correctly installed.
• OWL 1.0;
  

 Overview

  The code provided herein will help you load OWL ontologies and annotations into JESS, an inference engine that uses a CLIPS-like language. Using JESS you will then be able to reason about these ontologies and annotations. The code is organized into three main files:

• OWL Meta-model (OWL.clp) : a file describing the OWL meta-model in the JESS language. It is to be loaded directly into the JESS engine.
• Ontology Stylesheet (OWLOntology2Jess.xsl) : an XSLT stylesheet that transforms a file with OWL schemata (in XML syntax) into a set of JESS assertions based on the OWL meta-model. The resulting assertions can the be loaded into the JESS engine.
  
• Annotation Stylesheet (OWLAnnotation2Jess.xsl) : an XSLT stylesheet that transforms a file with OWL annotations (in XML syntax) into a set of JESS assertions based on the OWL meta-model. The resulting assertions can the be loaded into the JESS engine.

 As shown in figure 1, these three files are used to provide the basis of an OWL inference engine based on JESS and they can be complemented with other stylesheets and other sources to add assertions and rules to the base (e.g. formal definitions, queries in QOWL, security enforcement, etc.)

Figure 1. Overall architecture

 Comments on the code

 OWL Meta-model

• Section (1): we declare a template to represent RDF triples as unordered facts in JESS .
• Section (2): the facts of the meta-models are defined using instances of the previous template.
• Section (3): the logic of the definitions of the meta-model of OWL is formalized as forward chaining rules that ensure the completion of the knowledge base with facts that correspond to positive entailments.
• Section (4): a set of exception rules to detect inconsistencies and to print exception messages for the corresponding negative entailments.
  

(4)

;;; Adding rule for coherence checking  ----------------------------------

;;; Check the extension of Nothing is empty
(defrule nothing-is-nothing  (declare (salience 100))
   (triple
          (predicate "http://www.w3.org/1999/02/22-rdf-syntax-ns#type")
          (subject ?s) (object "http://www.w3.org/2002/07/owl#Nothing")
        )
   =>
   (printout t "Error: " ?s " was found to be of type Nothing, which is not possible." crlf)
)

;;; A resource cannot be different from it-self
(defrule different-from-it-self  (declare (salience 100))
   (triple (predicate "http://www.w3.org/2002/07/owl#differentFrom") (subject ?o) (object ?o))
   =>
   (printout t "Error: " ?o " was found to be different from it-self, which is not possible." crlf)
)

;;; Two resources cannot be different and identical
(defrule different-and-identical  (declare (salience 100))
   (triple (predicate "http://www.w3.org/2002/07/owl#differentFrom") (subject ?o1) (object ?o2))
   (triple (predicate "http://www.w3.org/2002/07/owl#sameIndividualAs") (subject ?o1) (object ?o2))
   (test (neq ?o1 ?o2))
   =>
   (printout t "Error: " ?o1 " and " ?o2 " were found to be different and the same, which is not possible." crlf)
)

;;; A class cannot be disjoint with it-self
(defrule disjoint-with-it-self  (declare (salience 100))
   (triple (predicate "http://www.w3.org/2002/07/owl#disjointWith") (subject ?c) (object ?c))
   =>
   (printout t "Error: " ?c " was found to be disjoint with it-self, which is not possible." crlf)
)

;;; Two classes cannot be disjoint and equivalent
(defrule disjoint-and-equivalent  (declare (salience 100))
   (triple (predicate "http://www.w3.org/2002/07/owl#disjointWith") (subject ?c1) (object ?c2))
   (triple (predicate "http://www.w3.org/2002/07/owl#equivalentClass") (subject ?c1) (object ?c2))
   (test (neq ?c1 ?c2))
   =>
   (printout t "Error: " ?c1 " and " ?c2 " were found to be disjoint and equivalent, which is not possible." crlf)
)

 Ontology stylesheet

• Section (1): we extract the base of the XML document to get the namespace of the ontology and we ignore the root of the XML document and the rdf:RDF tag.
• Section (2):a template is declared for each element of the OWL meta-model to translate it into an appropriate triple.
• Section (3): a set of named templates is used to deal with recurrent tasks such as the extraction of an ID.
  

 Annotation stylesheet

  Finally comes the stylesheet to transform an annotation into a set of triples supposing that the OWL meta-model and the ontologies used by the annotation have been pre-loaded:

• Section (1): we extract the base of the XML document to get the namespace of the facts contained in the annotation and we ignore the root of the XML document and the rdf:RDF tag.
• Section (2): a set of named templates uses the alternating nesting of objects and properties to transform the annotation into corresponding triples.
  
• Section (3): a set of named templates is used to deal with recurrent tasks such as the extraction of an ID.
  

 Copyright Notice and Disclaimer

Acknowledgements