WonderWeb. Ontology Infrastructure for the Semantic Web. IST Project Review Meeting, 11 th March, WP1: Language Architecture Sean Bechhofer University of Manchester

WonderWeb. Ontology Infrastructure for the Semantic Web. IST Project Review Meeting, 11 th March, Languages A language standard provides some of the “glue” that allows applications to interoperate.

WonderWeb. Ontology Infrastructure for the Semantic Web. IST Project Review Meeting, 11 th March, 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.

WonderWeb. Ontology Infrastructure for the Semantic Web. IST Project Review Meeting, 11 th March, 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

WonderWeb. Ontology Infrastructure for the Semantic Web. IST Project Review Meeting, 11 th March, 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

WonderWeb. Ontology Infrastructure for the Semantic Web. IST Project Review Meeting, 11 th March, 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)

WonderWeb. Ontology Infrastructure for the Semantic Web. IST Project Review Meeting, 11 th March, 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 Full DL Lite

WonderWeb. Ontology Infrastructure for the Semantic Web. IST Project Review Meeting, 11 th March, 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

WonderWeb. Ontology Infrastructure for the Semantic Web. IST Project Review Meeting, 11 th March, 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.

WonderWeb. Ontology Infrastructure for the Semantic Web. IST Project Review Meeting, 11 th March, 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 (1 st Order reasoner)

WonderWeb. Ontology Infrastructure for the Semantic Web. IST Project Review Meeting, 11 th March, 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

WonderWeb. Ontology Infrastructure for the Semantic Web. IST Project Review Meeting, 11 th March, 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).

WonderWeb. Ontology Infrastructure for the Semantic Web. IST Project Review Meeting, 11 th March, 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. spouse earns owns

WonderWeb. Ontology Infrastructure for the Semantic Web. IST Project Review Meeting, 11 th March, 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.

WonderWeb. Ontology Infrastructure for the Semantic Web. IST Project Review Meeting, 11 th March, 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 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)

WonderWeb. Ontology Infrastructure for the Semantic Web. IST Project Review Meeting, 11 th March, Next Steps Further Working Groups –Semantic Web Best Practice (GS) –Data Access –Rules Prototype implementations of SWRL based on 1 st order reasoners. Further Query Language investigations Further language extensions: –Complex roles [HS03] –Concrete datatype reasoning [PH03] –Keys [LAHS03]

WonderWeb. Ontology Infrastructure for the Semantic Web. IST Project Review Meeting, 11 th March, 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, [GHVD03] Benjamin N. Grosof, Ian Horrocks, Raphael Volz, and Stefan Decker. Description logic programs: Combining logic programs with description logic. WWW2003

WonderWeb. Ontology Infrastructure for the Semantic Web. IST Project Review Meeting, 11 th March, 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 [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