Wp1 language architecture
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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

WP1: Language Architecture

Sean Bechhofer

University of Manchester


Languages

Languages

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


Wp1 language architecture1

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.


Ontology language

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


Owl process

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 contributions

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)


Owl layering

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


Owl layering1

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


Layering and species recognition

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 contributions1

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)


Owl api

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


Rules swrl

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).


Rules

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


Rules dlp

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.


Query languages

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)


Next steps

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]


Relevant publications

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


Relevant publications1

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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