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An inference engine for the semantic web. Naudts Guido Student at the Open University Netherlands. Case study. The layers of the semantic web. SGML and HTML. SGML and HTML HTML is an application of SGML. An application is a set of SGML tags and attribute .
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An inference engine for the semantic web Naudts Guido Student at the Open University Netherlands
SGML and HTML SGML and HTML HTML is an application of SGML. An application is a set of SGML tags and attribute . The tags are used for the presentation of the document. Here's a simple HTML document: <html> <head> <title> My home page </title> </head> <body> <h1>Hello there!</h1> <p> <font color="blue">Welcome to my home page!</font> </p> </body> </html>
XML Properties • Meta-language • Subset of SGML • Definition of tags –standardisation? • Hierarchical • Namespaces = mix of languages!
XML Example <?xml version="1.0 ?> <!DOCTYPE bookSYSTEM"http://somesite.org/book.dtd"> <book id="nielsen01"> <title> Designing Web Usability </title> <info> <key> Design </key> <key> Internet </key> <isbn> 1-56205-810-X </isbn> </info> </book>
DTD Example <!DOCTYPE book [ <!ELEMENT book (title, subtitle?, author+, info) > <!ATTLIST book id CDATA #REQUIRED > <!ELEMENT title PCDATA > <!ELEMENT subtitle PCDATA > <!ELEMENT author PCDATA > <!ELEMENT info (key*, isbn) > <!ELEMENT key PCDATA > <!ELEMENT isbn PCDATA > ]>
Basics of RDF • Anything can be a resource. • Resources have URIs. • Resources have properties. • Properties have values and types. • An RDF document makes statements about resources and their properties.
RDF Properties • RDF is a language ==> syntax and semantics • XML syntax • Notation 3 syntax
A Simple Example • “Jan Hanford created the J.S. Bach homepage.” • The J.S. Bach homepage is a resource • It has a URI (http://www.jsbach.org) • It has a property • The property has a type of “creator” • The property has a value of “Jan Hanford”
http://www.jsbach.org Jan Hanford RDF Graph Property Type Property Value Resource has the creator
Translated to (simplified) RDF: Resource <RDF> <Description about="http://www.jsbach.org"> <Creator>Jan Hanford</Creator> </Description> </RDF> Property Value Property Type
Namespaces added: <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:dc="http://purl.org/DC/"> <rdf:Description about="http://www.jsbach.org/"> <dc:Creator>Jan Hanford</dc:Creator> </rdf:Description> </rdf:RDF>
RDF Schema example <!-- $Id: animal.rdf,v 1.2 2001/10/01 00:12:34 amdus Exp $ --> <!-- A simple RDF file for parser testing --> <rdf:RDF xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:daml="http://www.daml.org/2001/03/daml+oil#" xmlns="http://www.daml.org/2000/12/daml+oil#"> <rdfs:Class rdf:ID="Animal"> <rdfs:label>Animal</rdfs:label> <restrictedBy> <Restriction> <onProperty rdf:resource="#parent"/> <cardinality>2</cardinality> </Restriction> </restrictedBy> </rdfs:Class> </rdf:RDF>
Ontology • Terms used to describe an area of knowledge • Classes, relationships, properties, subclasses • Definition of semantics • Avoid tower of Babel
Closed world assumption • Case study: Jos is member of W3C. All members of W3C are entitled to recieve W3C-mail. Therefore Jos is entitled to recieve W3C-mail. We pose the query: Can Jim recieve mail from the W3C? Jim is not in the list answer = no!!! Because of closed world assumption.
Open world assumption • Case study: I have a list of important internet sites; site A is on my list site A is important. Site B is not on my list site B is not important??? Conclusion : Open World is de default assumption, Closed World must be enforced.
Proof • Proof validation, not generation • Simple things: a b, a thus b. • validation: do the URI’s exist, are the steps followed in the reasoning valid?
Trust • Build a web of trust • Truth = trust I believe x • Absolute truth ==> a pinguin is a bird • Contradictions between trusted parties?
Thesis questions 1 • What is the best way for realising an inference engine so that the restrictions that are imposed by the structure of the World Wide Web on the Semantic Web are met ? • can meta-logical frameworks be used to specify the inference engine of the semantic web?
Thesis questions 2 • what optimisation techniques can be used? • how can inconsistencies best be avoided? • which system of logic should be followed on the internet? • what is the interpretation of the logic i.e. what are its semantics?
Metalogical frameworks • Logic + methodology used to represent other logics and to reason about their metalogical properties
Optimisation and consistency • Reorder clauses • Limit the search space • Detect inconsistencies i.e. logic contradiction; might be violation of constraints
N3 example part 1 • # $Id: authen.axiom.n3,v 1.2 2001/10/01 00:12:34 amdus Exp $ • @prefix log: <http://www.w3.org/2000/10/swap/log#>. • @prefix : <authen#>. • <mailto:jos.deroo.jd@belgium.agfa.com> :member <http://www.agfa.com>. • <http://www.agfa.com> :w3cmember <http://www.w3.org>. • <http://www.agfa.com> :subscribed <mailto:w3c-ac-forum@w3.org/>. • {{:person :member :institution. • :institution :w3cmember <http://www.w3.org>. • :institution :subscribed :mailinglist} log:implies • {:person :authenticated :mailinglist}} a log:Truth; log:forAll :person, :mailinglist, :institution.
N3 example part 2 • # $Id: authen.lemma.n3,v 1.3 2001/10/15 22:40:11 amdus Exp $ • @prefix log: <http://www.w3.org/2000/10/swap/log#>. • @prefix : <authen#>. • _:who :authenticated <mailto:w3c-ac-forum@w3.org/>.
N3 example part 3 • # Generated with http://www.agfa.com/w3c/euler/#28.061 on Sat Dec 01 02:19:27 GMT+01:00 2001 • # for query http://www.agfa.com/w3c/euler/authen.lemma.n3 • # given [http://www.agfa.com/w3c/euler/authen.axiom.n3] • @prefix log: <http://www.w3.org/2000/10/swap/log#>. • @prefix : <http://www.agfa.com/w3c/euler/authen#>. • {<mailto:jos.deroo.jd@belgium.agfa.com> :member <http://www.agfa.com>. • <http://www.agfa.com> :w3cmember <http://www.w3.org>. • <http://www.agfa.com> :subscribed <mailto:w3c-ac-forum@w3.org/>} log:implies • {<mailto:jos.deroo.jd@belgium.agfa.com> :authenticated <mailto:w3c-ac-forum@w3.org/>}. • # Proof found for http://www.agfa.com/w3c/euler/authen.lemma.n3 in 3 steps (232 steps/sec)