Ontologies and the Semantic Web

Horrocks

owl rdf semantic web description logic ontologies

@article{horrocks:cacm-2008,
  title={Ontologies and the {Semantic Web}},
  author={Ian Horrocks},
  journal={Communications of the {ACM}},
  volume={51},
  number={12},
  month={December},
  year={2008}
}

Overviews RDF and OWL ontologies

IRIs: Internationalized Resource Identifiers

• A generalization of URLs (Uniform Resource Locators)

Ontologies in computer science are engineering artifacts

• A model of some aspect of the world
• Provides an explicit specification of the meaning of the vocabulary

OWL ontologies are similar to database schemas in many ways, but different in major ways

• OWL has open-world semantics
• OWL makes no unique-names assumption
• Ontology tools typically don't reject inconsistent updates, simply warn about the problem

Treating schema as constraints & balking at updates allows DBs to process queries very fast

• The additional inference is costly in OWL
• But can be useful for applications without complete information where inferences have high value

Primary DL reasoners

• FaCT++
• Racer
• Pellet

Ontology development tools

• SWOOP
• Protege
• TopBraid Composer

Very useful for development tools to generate hierarchy, report inconsistencies, be able to explain inferences and help debug the ontology

Very solid examples of ontologies playing critical roles in national medical information management systems

OWL 2.0 in development

• Based on more expressive SROIQ DL
  • Qualify cardinality restrictions
  • Asserts properties as reflexive, irreflexive, asymmetric, disjoint
  • Compose properties into property chains
  • Extended datatype and annotation supports
• Includes three profiles: http://www.w3.org/TR/owl2-profiles/
  • One based on DL Lite which reduces to SQL
  • One based on EL++
  • One based on DLP, which can be implemented in rule based systems

Other work

• SWRL: Semantic Web Rules Language
  • If Horn like rules are applied to named individuals only then it does not affect decidability of the DL; it's "DL-safe"
• SPARQL: RDF query language
• RDFa: Embed RDf in existing XHTML documents (already possible???)

Of note:

• Motik, Sattler, Studer. Query Answering for OWL-DL with Rules. Journal of Web Semantics, 2005.
• Cuenca Grau, Horrocks, Kazakov, Sattler. Module Reuse of Ontologies. JAIR, 2008.
• Doyle, Patil. Two Theses of Knowledge Representation. AI, 1991.
• Goodwin. Experiences of Using OWL at the Ordnance Survey. OWL Experiences and Directions Workshop, 2005. ceur-ws.org/Vol-188/
• Kalyanpur, Parsia, Sirin, Hendler. Debugging Unsatisfiable Classes is OWL Ontologies. Journal of Web Semantics, 2005.
• Lacy, Aviles, Fraser, Gerber, Mulvehill, Gaskill. Experiences Using OWL in Military Applications. OWL Experiences and Directions Workshop, 2005. ceur-ws.org/Vol-188/