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Knowledge Representation Guest Lecture - CSE 335/435

Knowledge Representation Guest Lecture - CSE 335/435. Jeff Heflin Lehigh University. Introduction. What is knowledge representation (KR)? subfield of artificial intelligence concerns storing general purpose information discovering the consequences of that information

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Knowledge Representation Guest Lecture - CSE 335/435

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  1. Knowledge RepresentationGuest Lecture - CSE 335/435 Jeff Heflin Lehigh University

  2. Introduction • What is knowledge representation (KR)? • subfield of artificial intelligence • concerns • storing general purpose information • discovering the consequences of that information • There are many KR languages • each with its pros and cons

  3. Semantic Networks canFly True Bird isa isa canFly False Canary Penguin instanceOf instanceOf Tweety Opus

  4. Frame Systems Bird canFly True slot numLegs 2 filler movesBy Wings covering Feathers Canary isa sings True Tweety instanceOf weight 22

  5. Description Logic • Father ≡ And(Male,Parent) • a father is a male parent • Parent ≡ AtLeast(1, hasChild) • a parent has at least one child • Band ⊑ All(members, Musician) • every member of a band is a musician • Trio ⊑ And(All(members, Musician), Exactly(3, members)) • a trio has exactly three members, all of whom are musicians

  6. Description Logic Inference • subsumption • is one class a subclass of another? • calculate implicit isa relations • classification • does an object belong to a class? • example • bobMale, bobParent • is bobFather true?

  7. Ontology • Definition • a logical theory that accounts for the intended meaning of a formal vocabulary (Guarino 98) • has a formal syntax and unambiguous semantics • inference algorithms can compute what logically follows • Structure • specifies at least a taxonomy • often richer definitions

  8. Cyc Upper Ontology From http://www.cyc.com/cycdoc/vocab/upperont-diagram.html

  9. The Semantic Web • Definition • The Semantic Web is not a separate Web but an extension of the current one, in which information is given well-defined meaning, better enabling computers and people to work in cooperation. (Berners-Lee et al., Scientific American, May 2001) • Applications • managing corporate web sites (intranets) • more automatic generation of web portals • better indexing of multimedia resources • web agents and web services • ubiquitous computing

  10. A Web of Ontologies revises commits to A1 A2 S1 extends extends extends extends revises revises C1 B1 B2 B3 D1 extends extends extends commits to commits to commits to S4 E1 F1 S5 commits to commits to S2 S3

  11. RDF and RDF Schema <rdf:Property rdf:ID=“name”> <rdfs:domain rdf:resource=“Person”> </rdf:Property> <rdfs:Class rdf:ID=“Chair”> <rdfs:subclassOf rdf:resource= “http://schema.org/gen#Person”> </rdfs:Class> rdfs:Class rdf:Property rdf:type rdf:type rdf:type g:Person rdfs:domain rdfs:subclassOf <rdf:RDF xmlns:g=“http://schema.org/gen” xmlns:u=“http://schema.org/univ”> <u:Chair rdf:ID=“john”> <g:name>John Smith</g:name> </u:Chair> </rdf:RDF> u:Chair g:name rdf:type g:name John Smith

  12. URIs and Namespaces • URI • Uniform Resource Identifier • includes URLs • but also anything that you can design an identification scheme for • helps to prevent collision of names • all the “symbols” in RDF are either URIs or Literals • Namespace • a mechanism for abbreviating URIs • by assigning a prefix for a URI fragment

  13. Web Ontology Language W3C Recommendation released Feb. 2004 based on RDF OWL markup linked to semantics <rdf:Description rdf:about=“”> <imports resource=“www.books.com/bookont”> <rdf:Description> <Book rdf:ID=“book26489”> <author>E.B. White</author> <title>Charlotte’s Web</title> <price>6.99</price> <subject rdf:resource=“&bookont;FictionChild”> </Book> semantic markup <Class ID=“Book”> <Property ID=“subject”> <domain resource=“#Book”> <range resource=“#Topic”> </Property> <Class ID=“FictionChild”> <subclassOf resource=“#Fiction”> <subclassOf resource=“#Childrens”> </Class> … imports bookont ontology

  14. OWL Class Constructors borrowed from Ian Horrocks

  15. OWL Axioms borrowed from Ian Horrocks

  16. OWL RDF Syntax <owl:Class rdf:ID=”Band”> <rdfs:subClassOf> <owl:Restriction> <owl:onProperty rdf:resource=”#hasMember” /> <owl:allValuesFrom resource=”#Musician” /> </owl:Restriction> </rdfs:subClassOf></owl:Class> A Band is a subset of the set of objects which only have Musicians as members

  17. OWL Inference • The head of an organization is also a member of it • A member of a terror organization is a terrorist • Therefore, the head of a terror organization is a terrorist <owl:Property rdf:about=“&s;head”> <rdfs:subPropertyOf rdfs:resource=“&s;member” /></owl:Property> <owl:Class rdf:about=“&t;Terrorist”> <owl:sameClassAs> <owl:Restriction> <owl:onProperty rdf:resource=“&s;member” /> <owl:someValuesFrom rdf:resource=“&s;TerroristOrg” /> </owl:Restriction> </owl:sameClassAs></owl:Class> type Bin Laden Terrorist head type Al Qaeda TerrorOrg

  18. Is the Semantic Web a Fad? • Open source Semantic Web tools • from IBM, Hewlett-Packard, Nokia, etc. • Commercial software vendors • Oracle 11g RDBMS supports RDF and much of OWL • Adobe’s products use RDF to provide metadata for documents, photos • Semantic Web specific companies: TopQuadrant, Aduna Software, etc. • ~65 million Semantic Web documents (as of October 2009) • Yahoo SearchMonkey uses RDF to present richer search results • Google now indexes RDFa (a means for embedding RDF in web pages) • Semantic Web enabled sites • Data.gov: much of U.S. government’s open data is available in RDF • Newsweek: annotates articles with RDFa • BBC Music: exports RDF playlists, RDF for all artists • Harper’s Magazine: connects articles to events on a timeline • DBPedia: a Semantic Web version of Wikipedia

  19. Conclusion • KR has a long and impressive history • The Semantic Web is a direct descendant of KR research • The Semantic Web is growing at an extraordinary rate • it has potential to revolutionize the Web!

  20. For more information... • For more on the Semantic Web • http://www.cse.lehigh.edu/~heflin/ • http://www.semwebcentral.org/ • http://www.w3.org/2001/sw/ • http://www.semanticweb.org/ • Contact me • heflin@cse.lehigh.edu

  21. The End

  22. Evolution of Web Standards presentation-oriented markup HTML <tr><td><b>Charlotte’s Web</b> - E.B. White, Garth Williams. <font color=“Red”>$6.99</font> </td></tr> content-oriented markup XML <book> <title>Charlotte’s Web</title> <author>E.B. White</author> <author>Garth Williams</author> <price units=“USD”>6.99</price> <subject>Children’s Fiction</subject> </book>

  23. Species of OWL • OWL Full • very expressive (e.g., classes as instances) • theoretical properties not well understood • OWL DL • has a standard model theoretic semantics • OWL Lite • subset of OWL DL • easier to reason with

  24. Semantic Web Challenges • The Web is distributed • many sources, varying authority • inconsistency • The Web is dynamic • representational needs may change • The Web is enormous • systems must scale well • The Web is an open-world

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