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Chapter 5 semantic web
 

Chapter 5 semantic web

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    Chapter 5 semantic web Chapter 5 semantic web Presentation Transcript

    • Chapter 5Knowledge Representation &Description Logic
    • Introduction• Logic based Knowledge Representation formalisms – Descendants of semantic networks – KL-ONE – Domain description in the form of concepts (classes), roles (properties, relationships) and individuals. – A knowledge base (KB) is a pair K = < A> where T T, , is a TBox, and A is an Abox.Akerkar: Foundations of © Narosa Publishing House, 2009 2Semantic Web.
    • Introduction• Description Logic: set of concept and role forming operators – ALC is a type of description logics. – Concepts constructed using u, t, :, 9 and 8• S used for ALC with transitive roles (R+)Akerkar: Foundations of © Narosa Publishing House, 2009 3Semantic Web.
    • DL Architecture Knowledge Base =============== Inference Interface Tbox (schema) System Abox (data)Akerkar: Foundations of © Narosa Publishing House, 2009 4Semantic Web.
    • Syntax & Semantics ALC provides two special classes as shortcuts:Akerkar: Foundations of © Narosa Publishing House, 2009 5Semantic Web.
    • Example 5.11Akerkar: Foundations of © Narosa Publishing House, 2009 6Semantic Web.
    • ALC Description Logic• Two kinds of concept descriptions – elementary descriptions and – complex descriptions• ALC concept formulas are built up from basic concept names and roles.• ALC statements relate named or anonymous concepts by means of one of the following: – Inclusion, – inverse inclusion, and – Equivalence.Akerkar: Foundations of © Narosa Publishing House, 2009 7Semantic Web.
    • Reasoning About Knowledge• Description logics uses tableau algorithms – for deciding concept satisfiability with respect to a knowledge base. – A tableau algorithm for a DL language contains the following elements: • A completion graph, known as tableau, which represents a model of the DL language. • A set of tableau expansion rules to construct a complete and consistent completion graph. • A set of blocking rules to detect infinite cyclic models and ensure termination. • A set of clash conditions to detect logic contradictions.Akerkar: Foundations of © Narosa Publishing House, 2009 8Semantic Web.
    • CLASSIC• Example 5.1: Express the sentences in the CLASSIC language. – The set of men with at most two daughters. AND(Man, AT-MOST(2, Daughter). – The set of men with at most two daughters who are all professors in physics or mathematics departments. AND(Man, AT-MOST(2, Daughter)), ALL(Daughter, AND(Professor, FILLS(Department, Physics, Mathematics))).Akerkar: Foundations of © Narosa Publishing House, 2009 9Semantic Web.
    • CLASSIC & OWL• CAR = AND (FOURWHEELER, ALL (hasMaker, FACTORY)). <owl:Class rdf:ID="Car"> <rdfs:subClassOf rdf:resource="&vehicle;FourWheeler" /> ... <rdfs:subClassOf> <owl:Restriction> <owl:onProperty rdf:resource="#hasMaker" /> <owl:allValuesFrom rdf:resource="#Factory" /> </owl:Restriction> </rdfs:subClassOf> ... </owl:Class>Akerkar: Foundations of © Narosa Publishing House, 2009 10Semantic Web.
    • • CAR = AND (FOURWHEELER, AT-LEAST (1 engine)) <owl:Class rdf:ID="Car"> <rdfs:subClassOf rdf:resource="&vehicle;FourWheeler"/> <rdfs:subClassOf> <owl:Restriction> <owl:onProperty rdf:resource="#hasEngine"/> <owl:minCardinality rdf:datatype="&xsd;nonNegativeInteger">1</owl:minCardinality> </owl:Restriction> </rdfs:subClassOf> ... </owl:Class>Akerkar: Foundations of © Narosa Publishing House, 2009 11Semantic Web.
    • • SCOOTYPEPPLUS = AND (TWOWHEELER, FILLS (hasColour Pink)) <owl:Class rdf:ID="ScootyPepPlus"> <rdfs:subClassOf rdf:resource="#TwoWheeler"/> <rdfs:subClassOf> <owl:Restriction> <owl:onProperty rdf:resource="#hasColour" /> <owl:hasValue rdf:resource="#Pink" /> </owl:Restriction> </rdfs:subClassOf> </owl:Class>Akerkar: Foundations of © Narosa Publishing House, 2009 12Semantic Web.
    • Rule Languages• RuleMarkup in XML• WSMLAkerkar: Foundations of © Narosa Publishing House, 2009 13Semantic Web.
    • F-Logic ABC[hasLegalName -> ‘ABC Travel Agency’, hasOfficesIn ->> {Bangalore, Mumbai}, hasPhones ->> {00918023514537, 0091223885270}, hasEmployees ->> {Anita, Sunita, Punita}]. Anita[hasName -> ‘Miss Anita’, hasAddress -> AddressAnita[hasStreet -> ‘Nariman Point’, hasNumber -> 320, hasCity -> Mumbai]. BookingABCAnita[bookedBy -> ABC, bookedFor -> Anita, issuedFor -> LH635].Akerkar: Foundations of © Narosa Publishing House, 2009 14Semantic Web.
    • Company :: LegalEntity. Company[hasLegalName => STRING, hasOfficesIn =>> City, hasPhones =>> NUMBER, hasEmployees =>> Person]. Person :: LegalEntity. Person[hasName => STRING, hasAddress => Addresss]. Employee :: Person. Employee[isEmployedAt => Company]. Booking[bookedBy => LegalEntity, bookedFor => Person, issuedFor => Flight]. ABC : Company. Anita : Person. LH635 : Flight. BookingABCAnita : Booking.Akerkar: Foundations of © Narosa Publishing House, 2009 15Semantic Web.
    • Tools & Reasoners – Protégé: a free, open source ontology editor and a knowledge acquisition system. – OntoEdit – KAON2 – Pellet – FaCT+ – SESAME – OWL ValidatorAkerkar: Foundations of © Narosa Publishing House, 2009 16Semantic Web.
    • Suggested Readings 1. F. Baader, D. Calvanese, D. McGuinness, D. Nardi, and P. Patel-Schneider, editors. The Description Logic Handbook: Theory, Implementation and Applications. Cambridge University Press, 2003. 2. R. J. Brachman and al. Living with classic: When and how to use a kl-one-like language. In John Sowa, editor, Principles of Semantic Networks: Exploration in the Representation of Knowledge, pages 401--456. Morgan Kaufmann, 1991. 3. I. Horrocks, U. Sattler, Ontology reasoning in the SHOQ(D) description logic, in: Proc. of the 17th Int. Joint Conf. on Artificial Intelligence (IJCAI 2001), pp. 199–204, 2001. 4. I. Horrocks, P. F. Patel-Schneider, S. Bechhofer, and D. Tsarkov. OWL Rules: A Proposal and Prototype Implementation. Journal of Web Semantics, 3,1, 2005. 5. B. Motik, U. Sattler, and R. Studer. Query Answering for OWL- DL with Rules. Journal of Web Semantics 3,1, 2005. http://www.Websemanticsjournal.org/ps/pub/2005-3.Akerkar: Foundations of © Narosa Publishing House, 2009 17Semantic Web.