owl web ontology language

WEB ONTOLOGY LANGUAGE (OWL) 1

SeminarFor

Web Ontology Language (OWL)

Prepared by: Hussein Ali Ahmad Ghanim

6/19/20112


Web Ontology Language: OWL

Web Ontology Language Definition.

OverviewRequirements for ontology

languagesOWL Languages

- OWL, RDF, RDF(s), XMLReferences

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Web Ontology LanguageThe Web Ontology Language

(OWL) is a family of knowledge representation languages for authoring ontologies.

The languages are characterised by formal semantics and RDF/XML-based serializations for the Semantic Web.

Semantic Web led to requirement for a “web ontology language”

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OverviewFrom the overview of OWL1: The OWL Web

Ontology Language is designed for use by applications that need to process the content of information instead of just presenting information to humans.

OWL facilitates greater machine interpretability of Web content than that supported by XML, RDF, and RDF Schema (RDF-S) by providing additional vocabulary along with a formal semantics.

OWL has three increasingly-expressive sublanguages: OWL Lite, OWL DL, and OWL Full.

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Three species of OWL

Lite

DL

Full

Full: uses all the OWL languages primitives. It also allows to combine these primitives in arbitrary ways with RDF and RDF Schema. This includes the possibility to change the meaning of the pre-defined primitives, by applying the language primitives to each other.The advantage of OWL Full is that it is fully upward compatible with RDF, both syntactically and semantically.The disadvantage of OWL Full is the language has become so powerful as to be undecidable, dashing any hope of complete (let alone efficient) reasoning support.

DL = Description Logicis a sublanguage of OWL Full which restricts the way in which the constructors from OWL and RDF can be used.The advantage of this is that it permits efficient reasoning support.The disadvantage is that we loose full compatibility with RDF.

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Three species of OWL

Lite: - An ever further restriction limits OWL DL to a subset of the language constructors. For example, OWL Lite excludes enumerated classes, disjointness statements and arbitrary cardinality (among others).- The advantage of this is a language that is both easier to grasp (for users) and easier to implement (for tool builders).- The disadvantage is of course a restricted expressivity. 6/19/20112


Requirements for ontology languages

Ontology languages allow users to write explicit, formal conceptualizations of domains models. The main requirements are:

1. a well-defined syntax2. a well-defined semantics3. efficient reasoning support4. sufficient expressive power5. convenience of expression.

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What is OWL? W3C Recommendation, February 2004.

◦ web standard Web Ontology Language built on top of RDFRDF: the Resource Description Framework

is an XML-based language to describe resources.

for processing information on the web designed to be interpreted by

computers, not for being read by people OWL is written in XML

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Why OWL?OWL is a part of the "Semantic Web Vision"

- a future where:◦ Web information has exact meaning ◦ Web information can be processed by computers ◦ Computers can integrate information from the

web

OWL was designed to ◦ provide a common way to process the content of

web information (instead of displaying it).◦ be read by computer applications (instead of

humans).

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OWL Languages

• Work on Semantic Web has defined of a collection or “stack” of languages. – These languages are then used to support the

representation and use of metadata.

• The languages provide basic machinery that we can use to represent the extra semantic information needed for the Semantic Web– XML– RDF– RDF(S)– OWL– …

OWL

Inte

gra

tion

RDF(S)

RDF

XML

Annota

tion

Inte

gra

tion

Infe

ren

ce

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OWL

• OWL: the language that is aimed to be thestandardised and broadly accepted ontology language of the Semantic Web.

• OWL: is an ontology language designed for the Semantic Web– It provides a rich collection of operators for forming

concept descriptions– It is a W3C standard, promoting interoperation and

sharing between applications– It has been designed to be compatible with existing

web standards

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The OWL languageThere are different syntactic forms of OWL: RDF’s XML-based syntax (primary syntax for OWL) an XML-based syntax that does not follow the RDF

conventions(more easily read by human users) see http://www.w3.org/TR/owl-xmlsyntax/

an abstract syntax (used in the language specification document) (much more compact and readable) see http://www.w3.org/TR/owl-semantics/

a graphic syntax based on the conventions of UML(an easy way for people to become familiar with OWL)

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XML provides a surface syntax for structured documents, but imposes no semantic constraints on the meaning of these documents.

XML Schema is a language for restricting the structure of XML documents and also extends XML with datatypes.

RDF is a datamodel for objects ("resources") and relations between them, provides a simple semantics for this datamodel, and these datamodels can be represented in an XML syntax.

RDF Schema is a vocabulary for describing properties and classes of RDF resources, with a semantics for generalization-hierarchies of such properties and classes.

OWL adds more vocabulary for describing properties and classes: among others, relations between classes (e.g. disjointness), cardinality (e.g. "exactly one"), equality, richer typing of properties, characteristics of properties (e.g. symmetry), and enumerated classes.

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Header

OWL documents are usually called OWL ontologies, and are RDF documents.

So the root element of a OWL ontology is an rdf:RDF element which also species a number of namespaces. For example:<rdf:RDFxmlns:owl ="http://www.w3.org/2002/07/owl#"xmlns:rdf ="http://www.w3.org/1999/02/22-rdf-syntax-ns#"xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"xmlns:xsd="http://www.w3.org/2001/XLMSchema#">

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An OWL ontology may start with a collection of assertions for housekeeping purposes. These assertions are grouped under an owl:Ontology element which contains comments, version control and inclusion of other ontologies. For example:

<owl:Ontology rdf:about="">

<rdfs:comment>An example OWL ontology</rdfs:comment>

<owl:priorVersionrdf:resource="http://www.mydomain.org/uni-ns-old"/>

<owl:importsrdf:resource="http://www.mydomain.org/persons"/>

<rdfs:label>University Ontology</rdfs:label>

</owl:Ontology>

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XMLa meta language that allows you

to create and format your own document markups

a method for putting structured data into a text file; these files are

- easy to read- unambiguous- extensible- platform-independent

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XMLa family of technologies:

- XML 1.0- Xlink - Xpointer & Xfragments - CSS, XSL, XSLT - DOM- XML Namespaces- XML Schemas

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The piecesthere are 3 components for XML

content: - the XML document- DTD (Document Type Declaration)- XSL (Extensible Stylesheet Language)

The DTD and XSL do not need to be present in all cases

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RDF Ontology Language?RDF stands for Resource Description Framework RDF is a framework for describing resources on

the web RDF provides a model for data, and a syntax so

that independent parties can exchange and use it RDF is designed to be read and understood by

computers RDF is not designed for being displayed to people RDF is written in XML RDF is a part of the W3C's Semantic Web Activity RDF is a W3C Recommendation RDFS language features allow for modeling

certain semantic aspects of a domain of interest

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RDF Schema (RDFS)is an extension to RDF.RDF Schema provides the

framework to describe application-specific classes and properties

Classes in RDF Schema is much like classes in object oriented programming languages. This allows resources to be defined as instances of classes, and subclasses of classes.

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RDFS Example<?xml version="1.0"?><rdf:RDF

xmlns:rdf= "http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#" xml:base= "http://www.animals.fake/animals#">

<rdf:Description rdf:ID="animal"><rdf:type rdf:resource="http://www.w3.org/2000/01/rdf-schema#Class"/>

</rdf:Description><rdf:Description rdf:ID="horse"> <rdf:type rdf:resource="http://www.w3.org/2000/01/rdf-

schema#Class"/> <rdfs:subClassOf rdf:resource="#animal"/> </rdf:Description></rdf:RDF>

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References1. Grigoris Antoniou1 and Frank van

Harmelen2(pages 5 - 7) www.csc.liv.ac.uk/~frank/teaching/comp08/lecture6.pdf

2. www.w3.org/TR/owl-features/3. www.w3.org/2004/OWL/4. www.csd.abdn.ac.uk

/.../OWLTheWebOntologyLanguage/5. static.twoday.net/71desa1bif/files/W3C-OWL-Ov

erview.pdf (pages )

6. https://wiki.imise.uni-leipzig.de/Lehre/2005WS/SOntEng/files?get

7. W3C Specification: http://www.w3.org/RDF/6/19/20112

http://www.csc.liv.ac.uk/~frank/teaching/comp08/lecture6.pdf


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

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

http://www.w3.org/2004/OWL/

http://www.w3.org/2004/OWL/

http://www.csd.abdn.ac.uk/.../OWLTheWebOntologyLanguage/

http://www.csd.abdn.ac.uk/.../OWLTheWebOntologyLanguage/



https://wiki.imise.uni-leipzig.de/Lehre/2005WS/SOntEng/files?get





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