What is OWL (and why should I give a hoot)?


by Peter F. Patel-Schneider

What is OWL (and why should I give a hoot)?

Abstract

OWL is the new ontology language produced by the W3C Web Ontology Working Group. As such, it is poised to be a major formalism for the design and dissemination of ontology information, particularly in the Semantic Web, a part of the World-Wide Web. OWL has influences from several communities, including the RDF community, the Description Logic community, and the frame community. These influences have resulted in a wide variety of requirements on OWL, several of which appear to be conflicting. OWL contains innovative solutions to several of these apparent conflicts but other conflicts have meant that it has not been possible to satisfy all the desired requirements for OWL.

In this talk I will describe the design and development of OWL concentrating on what makes OWL important, the relationship of OWL to other efforts, the innovative solutions that were required in its design, and the impact of the conflicting requirements on OWL.

Acknowledgments and Caveats

Acknowledgments

This talk reports on the work of a large group of researchers, including many in the W3C RDF Core and Web Ontology Working Groups, but, of course, has my particular prejudices built into it.

Caveats

Outline

  1. The Semantic Web
  2. Introduction to OWL
  3. Influences on OWL
  4. Design of OWL
  5. A new Semantic Web Vision
  6. Conclusions

The Semantic Web

The Semantic Web Vision

The Semantic Web

A (Modest) Example

Outline

  1. The Semantic Web
  2. Introduction to OWL
  3. Influences on OWL
  4. Design of OWL
  5. A new Semantic Web Vision
  6. Conclusions

OWL Ontology Fragment (in RDF/XML syntax)

Taken from the OWL wine and food ontologies.


<owl:Class rdf:ID="WhiteWine">
  <owl:intersectionOf rdf:parseType="Collection">
    <owl:Class rdf:about="#Wine" />
    <owl:Restriction>
      <owl:onProperty rdf:resource="#hasColor" />
      <owl:hasValue rdf:resource="#White" />
    </owl:Restriction>
  </owl:intersectionOf>
</owl:Class>

In other (more readable) words

A WhiteWine is precisely a Wine that has color White.
(From now on, I will not use the RDF/XML syntax!)

OWL Ontology Fragment (in DL syntax)

wine:Wine ≤ food:PotableLiquid ∩ (≥1 wine:madeFromGrape) ∩
                     (=1 wine:hasMaker) ∩ (∀ wine:hasMaker wine:Winery) ∩
                     (=1 wine:hasColor) ∩ ...
wine:madeFromGrape ≤ wine:Wine × wine:WineGrape
wine:hasColor ≤ wine:Wine × wine:WineColor
wine:WineColor = { wine:White, wine:Rose, wine:Red }
wine:White ≠ wine:Rose   wine:White ≠ wine:Red   wine:Rose ≠ wine:Red
wine:WineDescriptor = wine:WineTaste ∪ wine:WineColor

wine:WhiteWine = wine:Wine ∩ ( wine:hasColor wine:White )
wine:Riesling = wine:Wine ∩ (≤1 wine:madeFromGrape) ∩
                          (wine:madeFromGrape wine:RieslingGrape )
wine:Riesling ≤ wine:hasColor wine:White

wine:CorbansDryWhiteRiesling ∈ wine:Riesling ∩
                          (wine:hasMaker wine:Corbans) ∩ ...

Consequences of the Ontology Fragment

OWL is a logic, with an entailment (consequence) relationship.
For example, the ontology fragment above entails:

wine:Riesling ≤ wine:WhiteWine
wine:Riesling ≤ wine:WhiteWine ∩ (=1 wine:hasMaker)
wine:Riesling ≤ wine:WhiteWine ∪ (=7 wine:hasMaker)
wine:Riesling ∩ (wine:hasColor : wine:Red) ≤ wine:WineDescriptor
wine:CorbansDryWhiteRiesling ∈ wine:WhiteWine

Determining consequence in OWL is difficult

What you can't Say in OWL

What can be Done in OWL

Ontologies (An AI Approach)

What OWL Is

How OWL Fits into the Web

How OWL Fits into the World Wide Web

How OWL Fits into the Semantic Web

Why You Should Give a Hoot About OWL

Outline

  1. The Semantic Web
  2. Introduction to OWL
  3. Influences on OWL
  4. Design of OWL
  5. A new Semantic Web Vision
  6. Conclusions

Influences on OWL

Influences on OWL (Initial)

The Semantic Web

The Semantic Web Layer Cake

Semantic Web Tower

 

Not yet specified

Not yet specified

Not yet specified

OWL ontology language

RDF provides semantics

XML provides syntax

Identifiers are URIs (IRIs)


RDF

RDF Example

Exchange Syntax (RDF/XML) Abstract Syntax (RDF Triples)
<ex:Person:id="john"> john <rdf:type> <ex:Person>.
  <ex:name:datatype="&xsd;string"> john <ex:name>
    John Smith</ex:name>         "John Smith"^^xsd:string.
  <ex:spouse> john <ex:spouse> sally.
     <ex:Person:id="sally"> sally <rdf:type> <ex:Person>.
         <ex:father:resource="paul"/> sally <ex:father> paul.
    </ex:Person>
  </ex:spouse>
</ex:Person>
<rdf:description:about="#sally"> sally <ex:name>
  <ex:name:datatype="&xsd;string">         "Sally Brown"^xsd:string.
    Sally Brown</ex:name>
</rdf:description>

RDF Semantics

RDFS

RDFS Example

Information about the vocabulary in the previous example:

RDF and RDFS Summary

Frames

Description Logics

Description Logic Example

john ∈ Person ∩ name="John Smith"
<john,sally> ∈ spouse
Sally ∈ Person ∩ name="Sally Brown"
<sally,paul> ∈ father
spouse is symmetric
paul ∈ Person ∩ ≤ 0 spouse
Student ⊆ Person

Description Logic Inferences

john ∈ Person ∩ name="John Smith"
<john,sally> ∈ spouse
Sally ∈ Person ∩ name="Sally Brown"
<sally,paul> ∈ father
spouse is symmetric
paul ∈ Person ∩ ≤ 0 spouse
Student ⊆ Person

 
entails
 
sally ∈ Person ∩ ∃ spouse:Person
Student ∩ spouse:Student ⊆ Person ∩ spouse:Person
paul ∈ ∀ spouse : { sally }
mary ∈ (∀ spouse:Person ) ∪ (∃ spouse : ¬ { john } )

Determining Inference in DLs

Outline

  1. The Semantic Web
  2. Introduction to OWL
  3. Influences on OWL
  4. Design of OWL
  5. A new Semantic Web Vision
  6. Conclusions

(W3C) Design Criteria for OWL

  1. Part of the W3C Semantic Web
    • Thus an extension of RDF and RDFS with RDF syntax
  2. Nice syntax, similar to frames
  3. Clean semantics, as for Description Logics
    • To avoid problems with early, underspecified versions of RDF
  4. Sufficiently expressive to represent many useful ontologies
  5. Suitable for implementations

No research needed because already done for DAML+OIL

DAML+OIL

Influences on OWL

Influences on OWL (Initial)

Tensions in the Design

Syntax Tension

Syntax Solution

Are We Done?

Real Influences on OWL

Real Influences on OWL

OWL-RDF Compatibility, The Easy Parts

OWL-RDF Semantic Compatibility (part 1)

OWL DL

OWL Lite

The Current Semantic Web Vision

Warning: This is my interpretation of the current instantiation of the semantic web vision in W3C based on various statements made by people associated with W3C.

Vision:
Specify meaning of constructs in the World-Wide Web so that computers can process and understand them
Implementation of ``process''
All information in the Semantic Web will be written in RDF
  • Communication language (documents) will be RDF/XML
  • Names in the Semantic Web will be IRI references
  • Only the RDF triples extracted from the RDF/XML document carry information
Implementation of ``understand''
All information in the Semantic Web will understandable as RDF
  • Every Semantic Web language will be semantically compatible with RDF(S)

Why this Implementation of the Vision?

Effect of the Vision on OWL

Giving Meaning to Triples

clash1

OWL-RDF Semantic Compatibility (part 2)

OWL-RDF Semantic Compatibility (part 2)

Semantic Compatibility (part 2)

The State of OWL

Outline

  1. The Semantic Web
  2. Introduction to OWL
  3. Influences on OWL
  4. Design of OWL
  5. A new Semantic Web Vision
  6. Conclusions

Going Forward

Can the Semantic Web vision be extended to the next (logic) level?

A New Implementation of the Vision

Vision:
Specify meaning of constructs in the World-Wide Web so that computers can process and understand them
Implementation of ``process''
All information in the Semantic Web will be written in RDFXML
  • Communication language (documents) will be RDF/XML
  • Names in the Semantic Web will be IRI references
  • Only the RDF triples extracted from the RDF/XML document carry information
Implementation of ``understand''
Everything in the Semantic Web will be a semantic extension of RDF(S)
  • Every Semantic Web language will be semantically compatible with RDF(S)
  • Semantic Web languages will have a means of referencing documents in the Semantic Web

A New Implementation of the Vision

Outline

  1. The Semantic Web
  2. Introduction to OWL
  3. Influences on OWL
  4. Design of OWL
  5. A new Semantic Web Vision
  6. Conclusions

Conclusions

Resources

DAML+OIL
http://www.daml.org/2001/03/daml+oil-index.html
OWL (W3C Web Ontology Working Group)
http://www.w3.org/2001/sw/WebOnt/
RDF (W3C RDF Core Working Group)
http://www.w3.org/2001/sw/RDFCore/