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1 An inference engine An inference engine for the semantic web for the semantic web Naudts Guido Student at the Open University Netherlands
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An inference engine for the An inference engine for the semantic websemantic web
Naudts Guido
Student at the Open University
Netherlands
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Case studyCase study
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The layers of the semantic webThe layers of the semantic web
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SGML and HTMLSGML 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>
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• XML PropertiesXML Properties
Meta-languageSubset of SGMLDefinition of tags –standardisation?HierarchicalNamespaces = mix of languages!
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XML ExampleXML Example<?xml version="1.0 ?> <!DOCTYPE book SYSTEM "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>
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DTD ExampleDTD 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 > ]>
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XML Schema exampleXML Schema example
<?xml version ="1.0"?> <schema xmlns:xsd = "http://www.w3.org/1999/XMLSchema"> <element name = "book"> <complexType content = "elementOnly"> <sequence> <element ref = "title" /> <element ref = "subtitle" minOccurs = "0" maxOccurs = "1" /> <element ref = "author" minOccurs = "1" maxOccurs = "unbounded" /> </sequence> <attribute name = "id" use = "required" type = "string"/> </complexType> </element> <element name = "title"> <complexType content = "elementOnly" /> </element> ... </schema>
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The layers of the semantic webThe layers of the semantic web
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.
Basics of RDFBasics of RDF
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RDF PropertiesRDF Properties
RDF is a language ==>
syntax and semanticsXML syntaxNotation 3 syntax
A Simple ExampleA 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”
RDF GraphRDF Graph
http://www.jsbach.org Jan Hanfordhas the creator
Resource Property Type Property Value
Translated to (simplified) RDF:Translated to (simplified) RDF:
<RDF>
<Description about="http://www.jsbach.org">
<Creator>Jan Hanford</Creator>
</Description>
</RDF>
Resource
Property Value
Property Type
Namespaces added: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>
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RDF SchemaRDF Schema
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RDF Schema exampleRDF 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>
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The layers of the semantic webThe layers of the semantic web
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OntologyOntology
Terms used to describe an area of knowledge
Classes, relationships, properties, subclasses
Definition of semanticsAvoid tower of Babel
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The layers of the semantic webThe layers of the semantic web
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Closed world assumptionClosed 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.
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Open world assumptionOpen 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.
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The layers of the semantic webThe layers of the semantic web
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ProofProof
Proof validation, not generationSimple things: a b, a thus b. validation: do the URI’s exist, are the
steps followed in the reasoning valid?
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The layers of the semantic webThe layers of the semantic web
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TrustTrust
Build a web of trustTruth = trust I believe xAbsolute truth ==> a pinguin is a birdContradictions between trusted
parties?
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Structure of the projectStructure of the project
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Thesis questions 1Thesis 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?
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Thesis questions 2Thesis 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?
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Metalogical frameworksMetalogical frameworks
Logic + methodology used to represent other logics and to reason about their metalogical properties
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Optimisation and consistencyOptimisation and consistency
Reorder clausesLimit the search spaceDetect inconsistencies i.e. logic
contradiction; might be violation of constraints
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N3 example part 1N3 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:[email protected]> :member <http://www.agfa.com>.
<http://www.agfa.com> :w3cmember <http://www.w3.org>. <http://www.agfa.com> :subscribed <mailto:w3c-ac-
{{: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.
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N3 example part 2N3 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:[email protected]/>.
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N3 example part 3N3 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:[email protected]> :member <http://www.agfa.com>.
<http://www.agfa.com> :w3cmember <http://www.w3.org>. <http://www.agfa.com> :subscribed <mailto:[email protected]/>}
log:implies {<mailto:[email protected]> :authenticated <mailto:w3c-
# Proof found for http://www.agfa.com/w3c/euler/authen.lemma.n3 in 3 steps (232 steps/sec)
