An inference engine for the semantic web

transcript

An inference engine for the An inference engine for the semantic websemantic web

Naudts Guido

Student at the Open University

Netherlands

Case studyCase study

The layers of the semantic webThe layers of the semantic web

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>

• XML PropertiesXML Properties

Meta-languageSubset of SGMLDefinition of tags –standardisation?HierarchicalNamespaces = mix of languages!

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>

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 > ]>

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>

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

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:

<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>

RDF SchemaRDF Schema

RDF Schema exampleRDF Schema example

<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>

</Restriction>

</restrictedBy>

</rdfs:Class>

</rdf:RDF>

OntologyOntology

Terms used to describe an area of knowledge

Classes, relationships, properties, subclasses

Definition of semanticsAvoid tower of Babel

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.

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.

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?

TrustTrust

Build a web of trustTruth = trust I believe xAbsolute truth ==> a pinguin is a birdContradictions between trusted

parties?

Structure of the projectStructure of the project

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?

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?

Metalogical frameworksMetalogical frameworks

Logic + methodology used to represent other logics and to reason about their metalogical properties

Optimisation and consistencyOptimisation and consistency

Reorder clausesLimit the search spaceDetect inconsistencies i.e. logic

contradiction; might be violation of constraints

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: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 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:w3c-ac-forum@w3.org/>.

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: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)

An inference engine for the semantic web

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