basic principles of semantic web
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Basic Principles of Semantic Web. Besnik Fetahu. What is Semantic Web?. The main vision of the inventor of the web Tim Berners-Lee was [1] : - PowerPoint PPT PresentationTRANSCRIPT
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Basic Principles of Semantic WebBesnik Fetahu
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What is Semantic Web?• The main vision of the inventor of the web Tim Berners-
Lee was [1]:
I have a dream for the Web [in which computers] become capable of analyzing all the data on the Web – the content, links, and transactions between people and computers. A ‘Semantic Web’, which should make this possible, has yet to emerge, but when it does, the day-to-day mechanisms of trade, bureaucracy and our daily lives will be handled by machines talking to machines. The ‘intelligent agents’ people have touted for ages will finally materialize.
Tim Berners-Lee, 1999
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What is Semantic Web?
Fig.1. Semantic Web Framework
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URI – Uniform Resource Identifier•URI can be as:
▫URL – Uniform Resource Locator▫URN – Uniform Resource Name
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XML – Extensible Markup Language•XML was designed as an option to send
documents easier across the web, it is considered an extensible language because it allows the user to define the mark-up elements.
<sentence><person href="http://aaronsw.com">I</person> just got a new pet <animal type="dog" ref="http://aaronsw.com/myDog">dog</animal>.</sentence>
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XML – Extensible Markup Language•Problems with the name of elements.•Uniquely identify element names using
XML namespaces.
<sentence xmlns="http://example.org/xml/documents/" xmlns:c="http://animals.example.net/xmlns/"><c: person c:href="http://aaronsw.com/">I</c:person> just got a new pet <c:animal>dog</c:animal>.</sentence>
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RDF – Resource Description Framework•Important layer of Semantic Web.•Created by triple element blocks
▫Object – Attribute – Value: O(A;V)▫Other notation: : [O]_A![V]▫Objects, and values can be interchanged.
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RDF – Resource Description Framework
• hasName (‘http://www.famouswriters.org/twain/mark’, "Mark Twain")• hasWritten (‘http://www.famouswriters.org/twain/mark’,
‘http://www.books.org/ISBN0001047582’)• title (‘http://www.books.org/ISBN0001047582’, "The Adventures of Tom
Sawyer")
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RDF – Resource Description Framework• RDF also uses XML syntax for describing relations
among these triple objects:
<rdf:Description rdf:about="http://www.famouswriters.org/twain/mark">
<s:hasName>Mark Twain</s:hasName><s:hasWritten
rdf:resource="http://www.books.org/ISBN0001047582"/></rdf:Description><rdf:Description
rdf:about="http://www.books.org/ISBN0001047582"><s:title>The Adventures of Tom Sawyer</s:title><rdf:type rdf:resource="http://www.description.org/schema#Book"/></rdf:Description>
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RDFS – RDF Schema• RDF Schema is a mechanism that lets developers
specify a vocabulary for RDF data and specify objects that can be applied to a particular attribute. About RDF Schema we can think about as a simple data typing model for RDF, this lets us create classes and properties with which we can describe very clearly the triple objects.
• RDF Schema starts with: http://www.w3.org/2000/01/rdf-schema#
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RDFS – RDF Schema
•:Book rdf:type rdfs:Class .• :bookTitle rdf:type rdf:Property .• :bookTitle rdfs:domain :Book .• :bookTitle rdfs:range rdfs:Literal .• :MyBook rdf:type :Book .• :MyBook :bookTitle "My Book" .
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RDFS – RDF Schema
Fig.5. Defining vocabulary and class hierarchy
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RDFS – RDF Schema• Now in the framework we have included three
layers:▫XML – which defines the syntactic layer▫RDF – which defines the structure layer using
triple objects▫RDFS – which defines the semantic layer, using
classes, properties and organizing all these in a hierarchical manner.
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Ontology, Inferences and DAML• Ontology: used to describe a world that consists of types,
properties, relationships … etc
• Ontology components in computer science are described using ontology languages like:▫ CycL▫ Dogma (Developing Ontology-Grounded Methods and
Applications)▫ F-Logic (Frame Logic)▫ KIF (Knowledge Interchange Format)▫ KL-ONE
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Ontology, Inferences and DAML•Markup language, that use markup
schema to encode knowledge:▫DAML + OIL▫Ontology Inference Layer (OIL)▫Web Ontology Language (WOL)▫Resource Description Framework▫RDF Schema▫SHOE
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Ontology, Inferences and DAML•Components included:
▫Individuals▫Classes▫Attributes▫Relations▫Function terms▫Restrictions▫Rules▫Axioms▫Events
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DAML + OIL
•DAML+OIL is an ontology language, it is used to describe the structure of a domain, the structure is described using classes and properties.
•DAML + OIL also uses axioms in order to present equivalencies and assertions.
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DAML + OIL
•DAML + OIL triples can be represented in different syntactic forms. It assigns for each triple of RDF a specific meaning. DAML+OIL only provides a semantic interpretation for those parts of an RDF graph that instantiate the schema
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DAML + OIL
•Ontology uses axioms to assert facts about classes like describing what it presents, e.g.:<daml:Class rdf:ID="Animal"/><daml:Class rdf:ID="Man"><rdfs:subClassOf rdf:resource="#Person"/><rdfs:subClassOf rdf:resource="#Male"/></daml:Class>
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DAML + OIL
•DAML provides methods of creating inverse properties, unambiguous properties, lists, restrictions etc.
•An example of these inverse properties::hasName daml:inverseOf :isNameOf :Sean :hasName "Sean“"Sean" :isNameOf :Sean
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Inference
•The principle of "inference" is quite a simple, being able to derive new data from data that you already know
▫:MyCar de:macht "160KW“▫de:macht daml:equivalentTo en:power ▫:MyCar de:power “160KW”
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Logic
•For the Semantic Web to become expressive enough we have to create a very powerful logical language in order to make inferences.
•There is a logical language that is currently in use by the semantic web Webized version of KIF (Knowledge Interchange Format).
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Logic{ { :Joe :loves :TheSimpsons } a log:Falsehood . { :Joe :is :Nuts } a log:Falsehood .} a log:Falsehood .
•This can be read as “it is not true that Joe does not love The Simpsons and is not nuts”.
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Trust and Proof
•This is the layer in which very little is done.
•This has to do with information provided by different sources ▫source a) states that “x is blue”▫source b) states that “x is red”
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Context
•The future applications on the semantic web will depend on context of the information to decide whether they trust or not the data. This is for example I receive information from a trustable source which he made some claims about the data, and because I know him I also trust that claim.
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Proof Languages• Proof languages are just languages used to verify the
correctness of a statement. An instance of proof language generally consists of inference items that are used to derive the information into a question, and the trust of each of these items can be checked.
• For example if we have a statement to prove that “Joe loves Mary”, and we have the items like “:Joe :loves :MSJ” and another item that uses daml to state that “:MSJ dam:equivalentTo :Mary”, and for these items we’ve got the checksums in order to verify the correctness of information.
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Proof Languages• Notation3:@prefix : <http://infomesh.net/2001/proofexample/#> .@prefix p: <http://www.w3.org/2001/07/imaginary-proof-ontology#> .@prefix log: <http://www.w3.org/2000/10/swap/log#> .@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .p:ProvenTruth rdfs:subClassOf log:Truth .# Proof
{ { <a.n3> p:checksum <md5:blargh>; log:resolvesTo [ log:includes { :Joe :loves :MJS } ] }
log:implies { :Step1 a p:Success } } a log:Truth . { { <b.n3> p:checksum <md5:test>;
log:resolvesTo [ log:includes { :MJS = :Mary } ] }log:implies{ :Step2 a p:Success } } a log:Truth .{ { :Step1 a p:Success . :Step2 a p:Success }log:implies { { :Joe :loves :Mary } a p:ProvenTruth } } a log:Truth