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Semantic Web

Lecture Notes Prepared by

Jagdish S. GangollyPh.D Program in Information Science

State University of New York at Albany

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Semantic Web

• ..is a mesh of information linked up in such a way as to be easily processable by machines, on a global scale. (http://infomesh.net/2001/swintro/)

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Motivation

• Need for interchangeability of information (information sharing)

• Need for interchangeability, translatability, uniformity of ontologies

• Need for improving precision in retrieval

• Need for web services based on understanding of data as well as metadata

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Semantic Web Components

– Data• Structure• Content• Format• Ontology

– Metadata• Representation Languages• Facility for metadata Interchange

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Data

• Data (Semi-structured as well as structured)

•Structure Tags: XML-Schema

•Content Tags: XML-Schema

•Ontology: Ontology representation languages

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Metadata I

• Representation languages based on First Order Logic

• KIF-based Ontolingua (http://www.ksl.stanford.edu/software/ontolingua/

• Loom (http://www.isi.edu/isd/LOOM/LOOM-HOME.html)

• Frame-Logic (http://www.cs.sunysb.edu/~kifer/dood/papers.html)

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Metadata II• Languages using standardised syntax

– Simple HTML Ontology Extensions (SHOE) (http://www.cs.umd.edu/projects/plus/SHOE/)

– XOL Ontology Exchange Language (XOL)(http://www.ai.sri.com/pkarp/xol/)

– Ontology Markup Language (OML and CKML) (Ontology Markup Language (OML and CKML)

– Resource Description Framework Schema Language (RDFS) (http://www.w3.org/TR/rdf-schema/)

– RiboWEB (http://www-smi.stanford.edu/projects/helix/riboweb/kb-pub.html)

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Metadata III– OIL (Ontology Interchange Language)

(http://www.ontoknowledge.org/oil/)– DAML+OIL (http://www.daml.org)– XFML+CAMEL (eXchangeable Faceted Metadata

Language + Compound term composition Algebraically-Motivated Expression Language) (http://www.csi.forth.gr/~tzitzik/XFML+CAMEL/)

• Good sources of information: http://www.cs.umd.edu/users/hendler/sciam/walkthru.htmlhttp://www.semanticweb.org/knowmarkup.html (These notes based on this source)

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Dublin Core• Metadata ElementsISO 15836:2003

Title Format

Creator Identifier

Subject Source

Description Language

Publisher Relation

Contributor Coverage

Date Rights

Type

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RDF (http://www.xml.com/pub/a/2002/01/30/daml1.html)

• XML based language that allows you to define classes and properties<rdfs:Class rdf:ID="Product">

<rdfs:label>Product</rdfs:label> <rdfs:comment>An item sold by Super Sports Inc.</rdfs:comment> </rdfs:Class>

<rdfs:Property rdf:ID="productNumber"> <rdfs:label>Product Number</rdfs:label> <rdfs:domain rdf:resource="#Product"/> <rdfs:range rdf:resource="http://www.w3.org/2000/01/rdf-schema#Literal"/> </rdfs:Property>

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DAML+OIL I (http://www.xml.com/pub/a/2002/01/30/daml1.html)• DAML+OIL also allows you to define

instances of classes and specify their properties

<Product rdf:ID="WaterBottle"> <rdfs:label>Water Bottle</rdfs:label> <productNumber>38267</productNumber> </Product>

• DAML+OIL allows datatyping<daml:DatatypeProperty rdf:ID="productNumber">

<rdfs:label>Product Number</rdfs:label> <rdfs:domain rdf:resource="#Product"/> <rdfs:range rdf:resource="http://www.w3.org/2000/10/XMLSchema#nonNegativeInteger"/> </daml:DatatypeProperty>

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DAML+OIL II (http://www.xml.com/pub/a/2002/01/30/daml1.ht

ml)

• Provides for uniqueness, equivalence, enumerations, disjoint classes, disjoint unions of classes, non-exclusive Boolean combinations of classes, intersection of classes, sub-classing, property restrictions

• Rich enough to model ontologies

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Web Ontology Language (OWL) I

• OWL Lite supports those users primarily needing a classification hierarchy and simple constraints.

• OWL DL supports those users who want the maximum expressiveness while retaining computational completeness (all conclusions are guaranteed to be computed) and decidability (all computations will finish in finite time).

• OWL Full is meant for users who want maximum expressiveness and the syntactic freedom of RDF with no computational guarantees.

Source: http://www.w3.org/TR/owl-features/

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Web Ontology Language (OWL) II