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WP1: Language Architecture

WP1: Language Architecture. Sean Bechhofer University of Manchester. Languages. A language standard provides some of the “glue” that allows applications to interoperate. WP1: Language Architecture. Development of Ontology Language Layer [ D1 ]

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WP1: Language Architecture

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  1. WP1: Language Architecture Sean Bechhofer University of Manchester

  2. Languages • A language standard provides some of the “glue” that allows applications to interoperate.

  3. WP1: Language Architecture • Development of Ontology Language Layer [D1] • Participation in W3C Web Ontology Language working group • Development of OWL standard • Editorship of key documents • Language Extensions • Query languages • Rules languages [D2] • WP1 has strong links with WP2: language design feeds into tool development and the development of tools is crucial to supporting language design.

  4. Ontology Language • OWL: a standard for a Web Ontology Language [OWL] • Now a W3C Recommendation (as of Feb 2004) • Use Cases and Requirements • Overview • Guide • Reference • Semantics and Abstract Syntax • Test Cases • Additional WG Notes • XML Concrete Syntax • Parsing OWL in RDF/XML

  5. OWL Process • August 2003: Candidate Recommendation • Exit criteria included implementation experience demonstrating that the specifications are implementable. • December 2003: Proposed Recommendation • Feb 2004: Recommendation • WG Note on parsing

  6. WonderWeb Contributions • Members of the WonderWeb consortium made significant contributions to the work of WebOnt • GS: co-chair of the working group • Use Cases and Requirements (RV) • Overview (FvH) • Guide (RV) • Reference (FvH, IH, SB) • Semantics and Abstract Syntax (IH) • Test Cases (IH, SB) • Parsing Note (SB)

  7. Full DL Lite OWL Layering • OWL has a layered architecture with successive layers providing more expressivity. • OWL Full corresponds to RDF. • OWL DL is OWL restricted to a DL/FOL fragment, allowing the use of DL reasoning techniques. • OWL Lite has further restrictions intended to ease implementation and provide easy entry for those familiar with frame-like languages. • Layered syntax and semantics • DL semantics are normative

  8. OWL Layering • OWL Lite • Quantification; Simple number restrictions (0/1) • Subclass and Equivalence axioms relating class names • OWL DL • Boolean expressions; Arbitrary number restrictions • Axioms relating arbitrary descriptions • Disjointness • OWL Full • No restrictions on separation of interpretations (class-as-instance, class-as-property etc.) • Redefinition of built-in vocabulary allowed

  9. Layering and Species Recognition • All OWL species are represented using RDF. • Thus a key task is species recognition – determining when an RDF document is in the DL or Lite fragment. • Not just checking whether vocabulary is present but how vocabulary is used. • This allows applications to use appropriate reasoning technology.

  10. WonderWeb Contributions • Tools developed during the project (WP2) were crucial to the success of the standardisation activity. • W3C standardisation requires demonstration of implementation experience, in particular: • Implementations of syntax checkers and recognisers. • OWL API including OWL Validator • Implementations of reasoners. • FaCT++ • Hoolet (1st Order reasoner)

  11. OWL API • The OWL API provides programmatic access to OWL ontologies. [BVL03] • Although this could be considered part of WP2 activity, the API has been important in promoting the use of OWL. • Includes RDF Parser and Validator [BC04] • demonstration that the specifications are implementable • useful in education and explanation – why are ontologies not in OWL DL? • framework for implementation of reasoners, again a key requirement of the standardisation activity. • Crossover interest from other communities • OMG’s RFP for Ontology Definition Metamodel

  12. Rules: SWRL • SWRL: A proposal for a Semantic Web Rule Language [HP04] • IH proposal editor. • Extends OWL with Horn-like rules • Rules can make use of OWL descriptions in both head and body • Currently produced under the auspices of the Joint US/EU ad hoc Agent Markup Language Committee • Soon to be W3C Note, which can then provide a starting point for forthcoming W3C Semantic Web Rules WG • Model-theoretic semantics (extension of OWL DL semantics).

  13. Rules • Extends OWL expressivity, allowing inference of relations: • hasParent(?x1,?x2)  hasBrother(?x2,?x3)  hasUncle(?x1,?x3) • An uncle is the brother of a parent. • Extends rules to allow existential quantification in rule heads: • HighEarner(?x)  spouse(?x, ?y)  earns(?x, ?a)  earns(?y, ?a)  owns.FastCar(?x) • If you’re a high earner and you earn the same amount as your spouse, then you own a fast car. earns earns owns spouse

  14. Rules: DLP • An investigation of the use of logic programming for OWL reasoning. [GHVD03, V03, VSM03] • Semantics-preserving translation of a fragment of OWL into Prolog. • SubClassOf( intersectionOf( Genius Composer) restriction( hasComposed allValuesFrom ( Masterpiece )) • Masterpiece(Y) :- Genius(X), Composer(X), hasComposed(X,Y) • Is the fragment sufficiently expressive for realistic ontologies? • Empirical analysis of ontologies available on the web.

  15. Query Languages • DQL (DAML Query Language) now updated as OWL Query Language • IH proposal editor. • Will form input document to W3C’s Data Access WG to be formed early 2004. • Query Example: • Query: (“Who owns a red car?”)Query Pattern: {(owns ?p ?c) (type ?c Car) (has-color ?c Red)}Must-Bind Variables List: (?p)May-Bind Variables List: (?c)

  16. Next Steps • Further Working Groups • Semantic Web Best Practice (GS) • Data Access • Rules • Prototype implementations of SWRL based on 1st order reasoners. • Further Query Language investigations • Further language extensions: • Complex roles [HS03] • Concrete datatype reasoning [PH03] • Keys [LAHS03]

  17. Relevant Publications • [D1] WonderWeb Deliverable D1: Ontology Language • [D2] WonderWeb Deliverable D2: Rules Language • [OWL] OWL Standardisation Documents • Technical Reports • WG Notes • [BC04] Sean Bechhofer and Jeremy J. Carroll. OWL DL: Trees or triples? To appear in WWW2004. • [BVL03] Sean Bechhofer, Raphael Volz, and Phillip Lord. Cooking the Semantic Web with the OWL API, ISWC 2003 • [HP04] Ian Horrocks and Peter F. Patel-Schneider. A proposal for an OWL rules language. To appear in WWW2004. • [HPH03] Ian Horrocks, Peter F. Patel-Schneider, and Frank van Harmelen. From SHIQ and RDF to OWL: The making of a web ontology language. Journal of Web Semantics, 1(1):7–26, 2003. • [GHVD03] Benjamin N. Grosof, Ian Horrocks, Raphael Volz, and Stefan Decker. Description logic programs: Combining logic programs with description logic. WWW2003

  18. Relevant Publications • [HS03] Ian Horrocks and Ulrike Sattler. The effect of adding complex role inclusion axioms in description logics. IJCAI 2003 • [LAHS03] Carsten Lutz, Carlos Areces, Ian Horrocks, and Ulrike Sattler. Keys, nominals, and concrete domains. IJCAI 2003 • [PH03] Jeff Pan and Ian Horrocks. Web ontology reasoning with datatype groups. ISWC2003 • [V03] Raphael Volz. Web Ontology Reasoning with logic databases. PhD thesis, Universitaet Karlsruhe (TH), February 2004. • [VSM03] Raphael Volz, Steffen Staab, and Boris Motik. Incremental maintenance of dynamic datalog programs. PSSS2003 • [VSM03a] Raphael Volz, Steffen Staab, and Boris Motik. Incremental Maintenance of Materialized Ontologies. ODBASE2003

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