Transcript WP1: Language Architecture

WP1: Language Architecture
Sean Bechhofer
University of Manchester
WonderWeb. Ontology Infrastructure for the Semantic Web. IST-2001-33052
Project Review Meeting, 11th March, 2004.
Languages
• A language standard provides some of the “glue” that allows
applications to interoperate.
WonderWeb. Ontology Infrastructure for the Semantic Web. IST-2001-33052
Project Review Meeting, 11th March, 2004.
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-2001-33052
Project Review Meeting, 11th March, 2004.
Ontology Language
• OWL: a standard for a Web Ontology Language [OWL]
• Now a W3C Recommendation (as of Feb 2004)
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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-2001-33052
Project Review Meeting, 11th March, 2004.
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-2001-33052
Project Review Meeting, 11th March, 2004.
WonderWeb Contributions
• Members of the WonderWeb consortium made significant
contributions to the work of WebOnt
• GS: co-chair of the working group
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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-2001-33052
Project Review Meeting, 11th March, 2004.
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
WonderWeb. Ontology Infrastructure for the Semantic Web. IST-2001-33052
Project Review Meeting, 11th March, 2004.
Full
DL
Lite
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-2001-33052
Project Review Meeting, 11th March, 2004.
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-2001-33052
Project Review Meeting, 11th March, 2004.
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)
WonderWeb. Ontology Infrastructure for the Semantic Web. IST-2001-33052
Project Review Meeting, 11th March, 2004.
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-2001-33052
Project Review Meeting, 11th March, 2004.
Rules: SWRL
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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-2001-33052
Project Review Meeting, 11th March, 2004.
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
WonderWeb. Ontology Infrastructure for the Semantic Web. IST-2001-33052
Project Review Meeting, 11th March, 2004.
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-2001-33052
Project Review Meeting, 11th March, 2004.
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)
WonderWeb. Ontology Infrastructure for the Semantic Web. IST-2001-33052
Project Review Meeting, 11th March, 2004.
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]
WonderWeb. Ontology Infrastructure for the Semantic Web. IST-2001-33052
Project Review Meeting, 11th March, 2004.
Relevant Publications
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[D1] WonderWeb Deliverable D1: Ontology Language
[D2] WonderWeb Deliverable D2: Rules Language
[OWL] OWL Standardisation Documents
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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
WonderWeb. Ontology Infrastructure for the Semantic Web. IST-2001-33052
Project Review Meeting, 11th March, 2004.
Relevant Publications
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[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
WonderWeb. Ontology Infrastructure for the Semantic Web. IST-2001-33052
Project Review Meeting, 11th March, 2004.