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{{Infobox W3C Standard
This is a preview for the new '''MathML rendering mode''' (with SVG fallback), which is availble in production for registered users.
| title            = OWL Web Ontology Language
| status            = Published
| year_started      = 2002
| editors          = Mike Dean, [[Guus Schreiber]]
| base_standards    = [[Resource Description Framework]], [[RDFS]]
| related_standards =
| abbreviation      = OWL
| domain            = [[Semantic Web]]
| website          = [http://www.w3.org/TR/owl-ref/ OWL Reference]
}}
{{Infobox W3C Standard
| title            = OWL 2 Web Ontology Language
| status            = Published
| year_started      = 2008
| editors          = W3C OWL Working Group
| base_standards    = Resource Description Framework, RDFS
| related_standards =
| abbreviation      = OWL 2
| domain            = Semantic Web
| website          = [http://www.w3.org/TR/owl2-overview/ OWL2 Overview]
}}
The '''Web Ontology Language''' ('''OWL''') is a family of [[knowledge representation]] languages for authoring [[Ontology (computer science)|ontologies]].
The languages are characterised by [[Semantics of programming languages|formal semantics]] and [[Resource Description Framework|RDF]]/[[XML]]-based serializations for the [[Semantic Web]]. OWL is endorsed by the [[World Wide Web Consortium]] (W3C)<ref>{{cite web |url=http://www.w3.org/TR/owl2-overview/ |title=OWL 2 Web Ontology Language Document Overview |date=2009-10-27 |publisher=W3C }}</ref> and has attracted academic, medical and commercial interest.


In October 2007, a new W3C working group<ref>[http://www.w3.org/2007/OWL W3C working group]</ref> was started to extend OWL with several new features as proposed in the OWL 1.1 member submission.<ref>{{cite web |url=http://www.w3.org/Submission/2006/10/ |title=Submission Request to W3C: OWL 1.1 Web Ontology Language |publisher=W3C |date=2006-12-19 }}</ref> W3C announced the new version of OWL on 27 October 2009.<ref name="w3.org">http://www.w3.org/2009/10/owl2-pr</ref> This new version, called OWL 2, soon found its way into semantic editors such as [[Protégé (software)|Protégé]] and [[semantic reasoner]]s such as Pellet,<ref>{{cite doi |10.1016/j.websem.2007.03.004 }}</ref><ref>[http://pellet.owldl.org/ Pellet]</ref> RacerPro,<ref>[http://www.racer-systems.com/ RacerPro]</ref> FaCT++<ref>{{cite doi |10.1007/11814771_26 }}</ref><ref>[http://code.google.com/p/factplusplus/ FaCT++]</ref> and HermiT.<ref>[http://hermit-reasoner.com/ HermiT]</ref>
If you would like use the '''MathML''' rendering mode, you need a wikipedia user account that can be registered here [[https://en.wikipedia.org/wiki/Special:UserLogin/signup]]
* Only registered users will be able to execute this rendering mode.
* Note: you need not enter a email address (nor any other private information). Please do not use a password that you use elsewhere.


The OWL family contains many species, serializations, syntaxes and specifications with similar names. OWL and OWL2 are used to refer to the 2004 and 2009 specifications, respectively. Full species names will be used, including specification version (for example, OWL2 EL).  When referring more generally, ''OWL Family'' will be used.
Registered users will be able to choose between the following three rendering modes:


== History ==
'''MathML'''
=== Early ontology languages ===
:<math forcemathmode="mathml">E=mc^2</math>
{{further|Knowledge_representation#History_of_knowledge_representation_and_reasoning}}
There is a long history of [[Ontology (computer science)|ontological]] development in philosophy and computer science. Since the 1990s, a number of research efforts have explored how the idea of [[knowledge representation]] (KR) from [[artificial intelligence]] (AI) could be made useful on the World Wide Web. These included languages based on [[HTML]] (called [[Simple HTML Ontology Extensions|SHOE]]), based on XML (called XOL, later [[Ontology Inference Layer|OIL]]), and various frame-based KR languages and knowledge acquisition approaches.


=== Ontology languages for the web ===
<!--'''PNG'''  (currently default in production)
:<math forcemathmode="png">E=mc^2</math>


In 2000 in the United States, [[DARPA]] started development of [[DARPA Agent Markup Language|DAML]] led by [[James Hendler]].<ref name="book:lacy:owl:c10">{{cite book |title=OWL: Representing Information Using the Web Ontology Language |last=Lacy |first=Lee W. |year=2005 |publisher=Trafford Publishing |location=Victoria, BC |isbn=1-4120-3448-5 |chapter=Chapter 10 }}</ref>
'''source'''
In March 2001, the ''Joint EU/US Committee on Agent Markup Languages'' decided that DAML should be merged with OIL.<ref name="book:lacy:owl:c10" />
:<math forcemathmode="source">E=mc^2</math> -->
The ''EU/US ad hoc Joint Working Group on Agent Markup Languages'' was convened to develop [[DAMLplusOIL|DAML+OIL]] as a web ontology language. This group was jointly funded by the DARPA (under the DAML program) and the European Union's [[Information Society Technologies]] (IST) funding project. DAML+OIL was intended to be a thin layer above [[RDFS]],<ref name="book:lacy:owl:c10" />
with [[Semantics of programming languages|formal semantics]] based on a [[description logic]] (DL).<ref name="Baader:2005">{{cite book |title=Mechanizing Mathematical Reasoning: Essays in Honor of Jörg H. Siekmann on the Occasion of His 60th Birthday |editor1-last=Hutter |editor2-last=Stephan |last1=Baader |first1=Franz |authorlink1=Franz Baader |last2=Horrocks |first2=Ian |authorlink2=Ian Horrocks |last3=Sattler |first3=Ulrike |authorlink3=Ulrike Sattler |year=2005 |publisher=Springer Berlin |location=Heidelberg, DE |isbn=978-3-540-25051-7 |chapter=Description Logics as Ontology Languages for the Semantic Web
|url=http://www.springerlink.com/content/mf848ceackyx |chapterurl=http://www.springerlink.com/content/axh20n8l34bc3ecb/ |editor-first=Dieter |editor-last=Hutter |editor-link=Dieter Hutter |editor2-first=Werner |editor2-last=Stephan |editor2-link=Werner Stephan}}</ref>


OWL started as a research-based<ref>{{cite web |url=http://www.w3.org/TR/2002/WD-owl-features-20020729/ |title=Feature Synopsis for OWL Lite and OWL: W3C Working Draft 29 July 2002 |publisher=W3C |date=2002-07-29 }}</ref> revision of DAML+OIL aimed at the semantic web.
<span style="color: red">Follow this [https://en.wikipedia.org/wiki/Special:Preferences#mw-prefsection-rendering link] to change your Math rendering settings.</span> You can also add a [https://en.wikipedia.org/wiki/Special:Preferences#mw-prefsection-rendering-skin Custom CSS] to force the MathML/SVG rendering or select different font families. See [https://www.mediawiki.org/wiki/Extension:Math#CSS_for_the_MathML_with_SVG_fallback_mode these examples].


=== Semantic web standards ===
==Demos==


{{quote|The Semantic Web provides a common framework that allows data to be shared and reused across application, enterprise, and community boundaries.|World Wide Web Consortium|''W3C Semantic Web Activity''<ref name="semantic_web_activity">{{cite web |url=http://www.w3.org/2001/sw/ |title=W3C Semantic Web Activity |author=World Wide Web Consortium |date=2010-02-06 |work= |accessdate=18 April 2010 }}</ref>}}
Here are some [https://commons.wikimedia.org/w/index.php?title=Special:ListFiles/Frederic.wang demos]:


{{further | Semantic Web}}


==== RDF schema ====
* accessibility:
** Safari + VoiceOver: [https://commons.wikimedia.org/wiki/File:VoiceOver-Mac-Safari.ogv video only], [[File:Voiceover-mathml-example-1.wav|thumb|Voiceover-mathml-example-1]], [[File:Voiceover-mathml-example-2.wav|thumb|Voiceover-mathml-example-2]], [[File:Voiceover-mathml-example-3.wav|thumb|Voiceover-mathml-example-3]], [[File:Voiceover-mathml-example-4.wav|thumb|Voiceover-mathml-example-4]], [[File:Voiceover-mathml-example-5.wav|thumb|Voiceover-mathml-example-5]], [[File:Voiceover-mathml-example-6.wav|thumb|Voiceover-mathml-example-6]], [[File:Voiceover-mathml-example-7.wav|thumb|Voiceover-mathml-example-7]]
** [https://commons.wikimedia.org/wiki/File:MathPlayer-Audio-Windows7-InternetExplorer.ogg Internet Explorer + MathPlayer (audio)]
** [https://commons.wikimedia.org/wiki/File:MathPlayer-SynchronizedHighlighting-WIndows7-InternetExplorer.png Internet Explorer + MathPlayer (synchronized highlighting)]
** [https://commons.wikimedia.org/wiki/File:MathPlayer-Braille-Windows7-InternetExplorer.png Internet Explorer + MathPlayer (braille)]
** NVDA+MathPlayer: [[File:Nvda-mathml-example-1.wav|thumb|Nvda-mathml-example-1]], [[File:Nvda-mathml-example-2.wav|thumb|Nvda-mathml-example-2]], [[File:Nvda-mathml-example-3.wav|thumb|Nvda-mathml-example-3]], [[File:Nvda-mathml-example-4.wav|thumb|Nvda-mathml-example-4]], [[File:Nvda-mathml-example-5.wav|thumb|Nvda-mathml-example-5]], [[File:Nvda-mathml-example-6.wav|thumb|Nvda-mathml-example-6]], [[File:Nvda-mathml-example-7.wav|thumb|Nvda-mathml-example-7]].
** Orca: There is ongoing work, but no support at all at the moment [[File:Orca-mathml-example-1.wav|thumb|Orca-mathml-example-1]], [[File:Orca-mathml-example-2.wav|thumb|Orca-mathml-example-2]], [[File:Orca-mathml-example-3.wav|thumb|Orca-mathml-example-3]], [[File:Orca-mathml-example-4.wav|thumb|Orca-mathml-example-4]], [[File:Orca-mathml-example-5.wav|thumb|Orca-mathml-example-5]], [[File:Orca-mathml-example-6.wav|thumb|Orca-mathml-example-6]], [[File:Orca-mathml-example-7.wav|thumb|Orca-mathml-example-7]].
** From our testing, ChromeVox and JAWS are not able to read the formulas generated by the MathML mode.


{{quote|a declarative representation language influenced by ideas from knowledge representation|World Wide Web Consortium|''Metadata Activity''<ref name="metadata.activity">{{cite web |url=http://www.w3.org/Metadata/Activity.html |title=Metadata Activity Statement |author=World Wide Web Consortium |date=2002-08-23 |publisher=World Wide Web Consortium |accessdate=20 April 2010 }}</ref>}}
==Test pages ==


In the late 1990s, the World Wide Web Consortium (W3C) ''Metadata Activity'' started work on [[RDFS|RDF Schema]] (RDFS), a language for [[Resource Description Framework|RDF]] vocabulary sharing. The RDF became a W3C [[web standards|Recommendation]] in February 1999, and RDFS a Candidate Recommendation in March 2000.<ref name="metadata.activity" /> In February 2001, the ''Semantic Web Activity'' replaced the Metadata Activity.<ref name="metadata.activity" /> In 2004 (as part of a wider revision of RDF) RDFS became a  W3C Recommendation.<ref>{{cite web |url=http://www.w3.org/Metadata/Activity.html |title=RDF Vocabulary Description Language 1.0: RDF Schema |author=World Wide Web Consortium |date=2002-08-23 | work=RDF Vocabulary Description Language 1.0 |publisher=World Wide Web Consortium |accessdate=20 April 2010 }}</ref>
To test the '''MathML''', '''PNG''', and '''source''' rendering modes, please go to one of the following test pages:
Though RDFS provides some support for ontology specification, the need for a more expressive ontology language had become clear.<ref name="book:lacy:owl:c9">{{cite book |title=OWL: Representing Information Using the Web Ontology Language |last=Lacy |first=Lee W. |year=2005 |publisher=Trafford Publishing |location=Victoria, BC |isbn=1-4120-3448-5 |chapter=Chapter 9 - RDFS}}</ref>
*[[Displaystyle]]
*[[MathAxisAlignment]]
*[[Styling]]
*[[Linebreaking]]
*[[Unique Ids]]
*[[Help:Formula]]


{{further | RDFS}}
*[[Inputtypes|Inputtypes (private Wikis only)]]
 
*[[Url2Image|Url2Image (private Wikis only)]]
==== Web-Ontology Working Group ====
==Bug reporting==
 
If you find any bugs, please report them at [https://bugzilla.wikimedia.org/enter_bug.cgi?product=MediaWiki%20extensions&component=Math&version=master&short_desc=Math-preview%20rendering%20problem Bugzilla], or write an email to math_bugs (at) ckurs (dot) de .
{{quote|As of Monday, the 31st of May, our working group will officially come to an end. We have achieved all that we were chartered to do, and I believe our work is being quite well appreciated.|James Hendler and Guus Schreiber|''So Long and thanks for all the fish''<ref name="web-ont" />}}
 
The World Wide Web Consortium (W3C) created the ''Web-Ontology Working Group'' as part of their Semantic Web Activity. It began work on November 1, 2001 with co-chairs James Hendler and Guus Schreiber.<ref name="web-ont">{{cite web |url=http://www.w3.org/2001/sw/WebOnt/#L151 |publisher=W3C |title=Web-Ontology (WebOnt) Working Group (Closed) }}</ref> The first working drafts of the [[abstract syntax]], reference and synopsis were published in July 2002.<ref name="web-ont" /> OWL became a formal [[Web standards|W3C recommendation]] on February 10, 2004 and the working group was disbanded on May 31, 2004.<ref name="web-ont" />
 
==== OWL Working Group ====
 
In 2005, at the ''OWL Experiences And Directions Workshop'' a consensus formed that recent advances in description logic would allow a more expressive revision to satisfy user requirements more comprehensively whilst retaining good computational properties.
In December 2006, the OWL1.1 Member Submission<ref name="owl1.1">{{cite web |url=http://www.w3.org/Submission/2006/SUBM-owl11-overview-20061219/ |title=OWL 1.1 Web Ontology Language |last1=Patel-Schneider |first1=Peter F. |authorlink1=Peter F. Patel-Schneider |last2=Horrocks |first2=Ian |date=2006-12-19 |publisher=World Wide Web Consortium |accessdate=26 April 2010 }}</ref> was made to the W3C. The W3C chartered the ''OWL Working Group'' as part of the Semantic Web Activity in September 2007. In April 2008, this group decided to call this new language OWL2, indicating a substantial revision.<ref name="grau.2008">{{cite doi |10.1016/j.websem.2008.05.001 }}</ref>
 
OWL 2 became a W3C recommendation in October 2009. OWL 2 introduces profiles to improve scalability in typical applications.<ref name="w3.org" />
 
=== Acronym ===
<!-- This section is linked from [[Owl (Winnie the Pooh)]] -->
{{quote|Why not be inconsistent in at least one aspect of a language which is all about consistency?|Guus Schreiber|''Why OWL and not WOL?''<ref>{{cite web |url=http://www.w3.org/People/Ivan/CorePresentations/RDFTutorial/Slides.html#%28114%29 |title=Why OWL and not WOL? |first=Ivan |last=Herman |authorlink=Ivan Herman |work=Tutorial on Semantic Web Technologies |publisher=World Wide Web Consortium |accessdate=18 April 2010 }}</ref>}}
 
The natural acronym for ''Web Ontology Language'' would be ''WOL'' instead of ''OWL''. Although the character [[Owl (Winnie the Pooh)|Owl]] from [[Winnie the Pooh]] wrote his name ''WOL'', the acronym ''OWL'' was proposed without reference to that character, as an easily pronounced acronym that would yield good logos, suggest wisdom, and honor [[William A. Martin]]'s ''One World Language'' knowledge representation project from the 1970s.
 
=== Adoption ===
 
A survey (published in 2006) of ontologies available on the web collected 688 OWL ontologies. Of these, 199 were OWL Lite, 149 were OWL DL and 337 OWL Full (by syntax). They found that 19 ontologies had in excess of 2,000 classes, and that 6 had more than 10,000. The same survey collected 587 RDFS vocabularies.<ref>{{cite doi |10.1007/11926078_49 }}</ref>
 
== Ontologies ==
 
{{main|Ontology (information science)}}
 
=== Introduction ===
 
{{quote|An ontology is an explicit specification of a conceptualization.|[[Tom Gruber]]|''  A Translation Approach to Portable Ontology Specifications''<ref name="TRG93">[[Tom Gruber|Gruber, Tom]] (1993); [http://tomgruber.org/writing/ontolingua-kaj-1993.pdf "A Translation Approach to Portable Ontology Specifications"], in ''Knowledge Acquisition'', 5: 199-199</ref>}}
 
The data described by an ontology in the OWL family is interpreted as a set of "individuals" and a set of "property assertions" which relate these individuals to each other. An ontology consists of a set of [[axioms]] which place constraints on sets of individuals (called "classes") and the types of relationships permitted between them. These axioms provide semantics by allowing systems to infer additional information based on the data explicitly provided. A full introduction to the expressive power of the OWL is provided in the W3C's ''OWL Guide''.
 
=== Example ===
 
An ontology describing families might include axioms stating that a "hasMother" property is only present between two individuals when "hasParent" is also present, and individuals of class "HasTypeOBlood" are never related via "hasParent" to members of the "HasTypeABBlood" class. If it is stated that the individual Harriet is related via "hasMother" to the individual Sue, and that Harriet is a member of the "HasTypeOBlood" class, then it can be inferred that Sue is not a member of "HasTypeABBlood".
 
== Species ==
=== OWL sublanguages ===
The W3C-endorsed OWL specification includes the definition of three variants of OWL, with different levels of expressiveness. These are OWL Lite, OWL DL and OWL Full (ordered by increasing expressiveness). Each of these sublanguages is a syntactic extension of its simpler predecessor. The following set of relations hold. Their inverses do not.
 
* Every legal OWL Lite ontology is a legal OWL DL ontology.
* Every legal OWL DL ontology is a legal OWL Full ontology.
* Every valid OWL Lite conclusion is a valid OWL DL conclusion.
* Every valid OWL DL conclusion is a valid OWL Full conclusion.
 
==== OWL Lite ====
 
OWL Lite was originally intended to support those users primarily needing a classification hierarchy and simple constraints. For example, while it supports [[cardinality]] constraints, it only permits cardinality values of 0 or 1. It was hoped that it would be simpler to provide tool support for OWL Lite than its more expressive relatives, allowing quick migration path for systems utilizing [[Thesaurus|thesauri]] and other [[Taxonomy|taxonomies]]. In practice, however, most of the expressiveness constraints placed on OWL Lite amount to little more than syntactic inconveniences: most of the constructs available in OWL DL can be built using complex combinations of OWL Lite features.<ref name="grau.2008" /> Development of OWL Lite tools has thus proven almost as difficult as development of tools for OWL DL, and OWL Lite is not widely used.<ref name="grau.2008" />
 
==== OWL DL ====
 
OWL DL was designed to provide the maximum expressiveness possible while retaining computational [[Complete theory|completeness]] (either φ or ¬φ belong), [[Decidability (logic)|decidability]] (there is an effective procedure to determine whether φ is derivable or not), and the availability of practical reasoning algorithms. OWL DL includes all OWL language constructs, but they can be used only under certain restrictions (for example, number restrictions may not be placed upon properties which are declared to be transitive). OWL DL is so named due to its correspondence with description logic, a field of research that has studied the logics that form the formal foundation of OWL.
 
==== OWL Full ====
OWL Full is based on a different semantics from OWL Lite or OWL DL, and was designed to preserve some compatibility with RDF Schema. For example, in OWL Full a class can be treated simultaneously as a collection of individuals and as an individual in its own right; this is not permitted in OWL DL. OWL Full allows an ontology to augment the meaning of the pre-defined (RDF or OWL) vocabulary. OWL Full is undecidable, so no reasoning software is able to perform complete reasoning for it.
 
=== OWL2 profiles ===
 
In OWL 2, there are three sublanguages of the language. OWL 2 EL is a fragment that has polynomial time reasoning complexity; OWL 2 QL is designed to enable easier access and query to data stored in databases; OWL 2 RL is a rule subset of OWL 2.
 
== Syntax ==
 
The OWL family of languages supports a variety of syntaxes. It is useful to distinguish ''high level'' syntaxes aimed at specification from ''exchange'' syntaxes more suitable for general use.
 
=== High level ===
 
These are close to the ontology structure of languages in the OWL family.
 
==== OWL abstract syntax ====
 
This high level syntax is used to specify the OWL ontology structure and semantics.<ref name="owl:spec:semantics_and_syntax">{{cite web |url=http://www.w3.org/TR/2004/REC-owl-semantics-20040210/syntax.html |title=OWL Web Ontology Language Semantics and Abstract Syntax |first1=Peter F. |last1=Patel-Schneider |first2=Ian |last2=Horrocks |first3=Hayes |last3=Patrick J. |authorlink3=Patrick J. Hayes |date=2004-02-10 |publisher=World Wide Web Consortium |accessdate=18 April 2010 }}</ref>
 
The OWL abstract syntax presents an ontology as a sequence of ''annotations'', ''axioms'' and ''facts''. Annotations carry machine and human oriented meta-data. Information about the classes, properties and individuals that compose the ontology is contained in axioms and facts only.
Each class, property and individual is either ''anonymous'' or identified by an [[URI|URI reference]]. Facts state data either about an individual or about a pair of individual identifiers (that the objects identified are distinct or the same). Axioms specify the characteristics of classes and properties. This style is similar to [[frame language]]s, and quite dissimilar to well known syntaxes for [[description logic]]s (DLs) and [[Resource Description Framework]] (RDF).<ref name="owl:spec:semantics_and_syntax" />
 
Sean Bechhofer, ''et al.'' argue that though this syntax is hard to parse, it is quite concrete. They conclude that the name ''abstract syntax'' may be somewhat misleading.<ref>{{cite web |url=http://owl.man.ac.uk/2003/concrete/20031210/ |title=OWL Web Ontology Language Concrete Abstract Syntax |first1=Sean |last1=Bechhofer |authorlink1=Sean Bechhofer |first2=Peter F. |last2=Patel-Schneider |first3=Daniele |last3=Turi |authorlink3=Daniele Turi |date=2003-12-10 |publisher=[[University of Manchester]] |accessdate=18 April 2010 }}</ref>
 
==== OWL2 functional syntax ====
 
This syntax closely follows the structure of an OWL2 ontology. It is used by OWL2 to specify semantics, mappings to exchange syntaxes and profiles.<ref name="owl2:spec:structure">{{cite web |url=http://www.w3.org/TR/2009/REC-owl2-syntax-20091027/ |title= OWL 2 Web Ontology Language Structural Specification and Functional-Style Syntax |last1=Motik |first1=Boris |authorlink1=Boris Motik |last2=Patel-Schneider |first2=Peter F. |last3=Parsia |first3=Bijan |authorlink3=Bijan Parsia |date=2009-10-27 |work=OWL 2 Web Ontology Language |publisher=World Wide Web Consortium |accessdate=18 April 2010 }}</ref>
 
=== Exchange syntaxes ===
{{Infobox file format
| name = OWL RDF/XML Serialization
| icon = [[Image:XML.svg|100px]]
| extension = .owx, .owl, .rdf
| mime = application/owl+xml, application/rdf+xml<ref>{{cite web |url=http://tools.ietf.org/html/rfc3870 |title=application/rdf+xml Media Type Registration |pages=2 |publisher=IETF |date=2004-09 |accessdate=2011-01-08 }}</ref>
| owner = [[World Wide Web Consortium]]
| standard = [http://www.w3.org/TR/owl2-xml-serialization/ OWL 2 XML Serialization] {{release date and age|2009|10|27}},<br/>[http://www.w3.org/TR/owl-ref/#MIMEType OWL Reference] {{release date and age|2004|02|10}}
| free = Yes
}}
 
==== RDF syntaxes ====
 
Syntactic mappings into [[Resource Description Framework|RDF]] are specified<ref name="owl:spec:semantics_and_syntax" /><ref name="owl2:spec:rdf">{{cite web |url=http://www.w3.org/TR/2009/REC-owl2-mapping-to-rdf-20091027/ |title= OWL 2 Web Ontology Language Mapping to RDF Graphs |last2=Motik |first2=Boris |last1=Patel-Schneider |first1=Peter F. |date=2009-10-27 |work=OWL 2 Web Ontology Language |publisher=World Wide Web Consortium |accessdate=18 April 2010 }}</ref>
for languages in the OWL family. Several RDF [[serialization| serialization formats]] have been devised. Each leads to a syntax for languages in the OWL family through this mapping. RDF/XML is normative.<ref name="owl:spec:semantics_and_syntax" /><ref name="owl2:spec:rdf" />
 
==== OWL2 XML syntax ====
 
OWL2 specifies an [[XML]] serialization that closely models the structure of an OWL2 ontology.<ref name="owl2:spec:xml">{{cite web |url=http://www.w3.org/TR/2009/REC-owl2-xml-serialization-20091027/ |title=OWL 2 Web Ontology Language XML Serialization |last1=Motik |first1=Boris |last2=Parsia |first2=Bijan |last3=Patel-Schneider |first3=Peter F. |date=2009-10-27 |work=OWL 2 Web Ontology Language |publisher=World Wide Web Consortium |accessdate=18 April 2010 }}</ref>
 
==== Manchester Syntax ====
 
The Manchester Syntax is a compact, human readable syntax with a style close to frame languages.
Variations are available for OWL and OWL2. Not all OWL and OWL2 ontologies can be expressed in this syntax.<ref name="ms:note">{{cite web |url= http://www.w3.org/TR/owl2-manchester-syntax/ |title= OWL 2 Web Ontology Language Manchester Syntax |last1=Horridge |first1=Matthew |authorlink1=Matthew Horridge |last2=Patel-Schneider |first2=Peter F. |date=2009-10-27 |work=W3C OWL 2 Web Ontology Language |publisher=World Wide Web Consortium |accessdate=18 April 2010 }}</ref>
 
=== Examples ===
 
* The W3C OWL 2 Web Ontology Language provides syntax examples.<ref name="owl2.primer">{{cite web |url=http://www.w3.org/TR/2009/REC-owl2-primer-20091027/ |title=OWL 2 Web Ontology Language Primer |last1=Hitzler |first1=Pascal |authorlink1=Pascal Hitzler |last2=Krötzsch |first2=Markus |authorlink2=Markus Krötzsch |last3=Parsia |first3=Bijan |last4=Patel-Schneider |first4=Peter F. |last5=Rudolph |first5=Sebastian |authorlink5=Sebastian Rudolph |date=2009-10-27 |work=OWL 2 Web Ontology Language |publisher=World Wide Wed Consortium |accessdate=2010-04-26 }}</ref>
 
==== Tea ontology ====
 
Consider an ontology for tea based on a Tea class. But first, an ontology is needed. Every OWL ontology must be identified by an [[URI]] (<nowiki>http://www.example.org/tea.owl</nowiki>, say). This is enough to get a flavour of the syntax. To save space below, preambles and prefix definitions have been skipped.
 
OWL2 Functional Syntax <source lang="xml">
Ontology(<http://example.com/tea.owl>
  Declaration( Class( :Tea ) )
)
</source>
 
OWL2 XML Syntax <source lang="xml">
<Ontology ontologyIRI="http://example.com/tea.owl" ...>
  <Prefix name="owl" IRI="http://www.w3.org/2002/07/owl#"/>
  <Declaration>
    <Class IRI="Tea"/>
  </Declaration>
</Ontology>
</source>
 
Manchester Syntax <source lang="xml">
Ontology: <http://example.com/tea.owl>
Class: Tea
</source>
 
RDF/XML syntax
<source lang="xml">
<rdf:RDF ...>
    <owl:Ontology rdf:about=""/>
    <owl:Class rdf:about="#Tea"/>
</rdf:RDF>
</source>
 
RDF/[[Turtle (syntax)|Turtle]] <source lang="xml">
<http://example.com/tea.owl> rdf:type owl:Ontology .
:Tea  rdf:type            owl:Class .
</source>
 
== Semantics ==
 
{{main | Semantics of programming languages}}
 
=== Relation to description logic ===
 
{{quote|In the beginning, IS-A was quite simple. Today, however, there are almost as many meanings for this inheritance link as there are knowledge-representation systems.|[[Ronald J. Brachman]]|''What ISA is and isn't''<ref>Brachman, Ronald J. (1983); ''What ISA is and isn't: An analysis of taxonomic links in semantic networks'', IEEE Computer, vol. 16, no. 10, pp. 30-36</ref>}}
 
Early attempts to build large ontologies were plagued by a lack of clear definitions. Members of the OWL family have [[model theory|model theoretic]] formal semantics, and so have strong [[logic]]al foundations.
 
[[Description logic]]s (DLs) are a family of logics that are decidable fragments of [[first-order logic]] with attractive and well-understood computational properties. OWL DL and OWL Lite semantics are based on DLs.<ref>{{cite web |url=http://www.cs.man.ac.uk/~horrocks/Publications/download/2003/HoPa03c.pdf |format=PDF |first=Ian |last=Horrocks |first2=Peter F. |last2=Patel-Schneider |title=Reducing OWL Entailment to Description Logic Satisfiability }}</ref>
They combine a syntax for describing and exchanging ontologies, and formal semantics that gives them meaning. For example, OWL DL corresponds to the [[SHOIN (D)]] description logic, while [[OWL2|OWL 2]] corresponds to the [[SROIQ(D)]] logic.<ref>{{cite book |title=Foundations of Semantic Web Technologies |first=Pascal |last=Hitzler |first2=Markus |last2=Krötzsch |first3=Sebastian |last3=Rudolph |publisher=CRCPress |date=2009-08-25 |isbn=1-4200-9050-X |url=http://www.semantic-web-book.org }}</ref> Sound, complete, terminating reasoners (i.e. systems which are guaranteed to derive every consequence of the knowledge in an ontology) exist for these DLs.
 
=== Relation To RDFS ===
 
OWL Full is intended to be compatible with [[RDF Schema]] (RDFS), and to be capable of augmenting the meanings of existing Resource Description Framework (RDF) vocabulary.<ref>{{cite web |url=http://www.w3.org/TR/2004/REC-owl-features-20040210/ |title=OWL Web Ontology Language Overview |first=Deborah |last=McGuinness |authorlink=Deborah McGuiness |first2=Frank |last2=van Harmelen |authorlink2=Frank van Harmelen |date=2004-02-10 |work=W3C Recommendation for OWL, the Web Ontology Language |publisher=World Wide Web Consortium |accessdate=18 April 2010}}</ref> A [[model theory]] describes the formal semantics for
RDF.<ref>{{cite web |url=http://www.w3.org/TR/2004/REC-rdf-mt-20040210/ |title=RDF Semantics |first=Patrick |last=Hayes |authorlink=Patrick Hayes |date=2004-02-10 |work=Resource Description Framework |publisher=World Wide Web Consortium |accessdate=18 April 2010 }}</ref> This interpretation provides the meaning of RDF and RDFS vocabulary. So, the meaning of OWL Full ontologies are defined by extension of the RDFS meaning, and OWL Full is a [[semantic extension]] of RDF.<ref>{{cite web |url=http://www.w3.org/TR/owl-semantics/rdfs.html |title=OWL Web Ontology Language Semantics and Abstract Syntax Section 5. RDF-Compatible Model-Theoretic Semantics |first=Peter F. |last=Patel-Schneider |first2=Patrick |last2=Hayes |first3=Ian |last3=Horrocks |date=2004-02-10 |work=W3C Recommendation for OWL, the Web Ontology Language |publisher=World Wide Web Consortium |accessdate=18 April 2010 }}</ref>
 
=== Open world assumption ===
 
{{quote|[The closed] world assumption implies that everything we don’t know is ''false'', while the open world assumption states that everything we don’t know is ''undefined''.|Stefano Mazzocchi|''Closed World vs. Open World: the First Semantic Web Battle''<ref>{{cite web |url=http://www.betaversion.org/~stefano/linotype/news/91/ |title=Closed World vs. Open World: the First Semantic Web Battle |first=Stefano |last=Mazzocchi |authorlink=Setfano Mazzocchi |date=2005-06-16 |accessdate=27 April 2010 }}</ref>}}
 
The languages in the OWL family use the [[open world assumption]]. Under the open world assumption, if a statement cannot be proven to be true with current knowledge, we cannot draw the conclusion that the statement is false.
 
==== Contrast to other languages ====
 
A [[relational database]] consists of sets of [[tuples]] with the same [[Attribute (computing)|attributes]]. [[SQL]] is a query and management language for relational databases. [[Prolog]] is a [[Logic programming|logical programming]] language. Both use the [[closed world assumption]].
 
== Terminology ==
Languages in the OWL family are capable of creating classes, properties, defining instances and its operations.
 
=== Instances ===
 
An ''instance'' is an object. It corresponds to a description logic ''individual''.
 
=== Classes ===
 
A ''class'' is a collection of objects. It corresponds to a description logic (DL) ''concept''.  A class may contain individuals, ''instances'' of the class. A class may have any number of instances. An instance may belong to none, one or more classes.
 
A class may be a ''subclass'' of another, inheriting characteristics from its parent ''superclass''. This corresponds to [[logical]] [[Is-a|subsumption]] and DL ''concept inclusion'' notated <math>\sqsubseteq</math>.
 
All classes are subclasses of owl:Thing (DL ''[[top type|top]]'' notated <math>\top</math>), the ''root'' class.
 
All classes are subclassed by owl:Nothing (DL ''[[bottom type|bottom]]'' notated <math>\bot</math>), the ''empty'' class. No instances are members of owl:Nothing. Modelers use owl:Thing and owl:Nothing to assert facts about all or no instances.<ref name="book:lacy:owl:c12">{{cite book |title=OWL: Representing Information Using the Web Ontology Language |last=Lacy |first=Lee W. |year=2005 |publisher=Trafford Publishing |location=Victoria, BC |isbn=1-4120-3448-5 |chapter=Chapter 12 }}</ref>
 
==== Example ====
For example, Employee could be the subclass of class owl:Thing while Dealer, Manager, and Labourer all subclass of Employee.
 
=== Properties ===
A property is a directed binary relation that specifies class characteristics. It corresponds to a description logic ''role''. They are attributes of instances and sometimes act as data values or link to other instances. Properties may possess logical capabilities such as being transitive, symmetric, inverse and functional. Properties may also have domains and ranges.
 
==== Datatype properties ====
 
Datatype properties are relations between instances of classes and RDF literals or XML schema datatypes. For example, modelName (String datatype) is the property of Manufacturer class. They are formulated using ''owl:DatatypeProperty'' type.
 
==== Object properties ====
 
Object properties are relations between instances of two classes. For example, ownedBy may be an object type property of the Vehicle class and may have a range which is the class Person. They are formulated using ''owl:ObjectProperty''.
 
=== Operators ===
 
Languages in the OWL family support various operations on classes such as union, intersection and complement. They also allow class enumeration, [[cardinality]], and disjointness.
 
== Public ontologies ==
=== Libraries ===
==== Biomedical ====
 
* [[Open Biomedical Ontologies|OBO Foundry]]<ref>[http://obofoundry.org OBO Foundry]</ref><ref>[http://www.berkeleybop.org/ontologies/ OBO Download Matrix]</ref>
* [[National Center for Biomedical Ontology|NCBO BioPortal]]<ref>[http://www.bioontology.org/ncbo/faces/pages/ontology_list.xhtml NCBO BioPortal]</ref>
* [[National Cancer Institute|NCI]] [http://www.cancer.gov/cancertopics/terminologyresources  Enterprise Vocabulary Services]
 
==== Miscellaneous ====
* [http://www.schemaweb.info/ SchemaWeb]
 
=== Standards ===
 
* [[Suggested Upper Merged Ontology]]<ref>[http://www.ontologyportal.org/translations/SUMO.owl.txt SUMO download]</ref>
* [[TDWG]]<ref>[http://rs.tdwg.org/ontology/voc/ TDWG LSID Vocabularies]</ref>
 
=== Browsers ===
 
The following tools include public ontology browsers:
 
* [[Protégé (software)|Protégé OWL]]<ref>[http://protege.stanford.edu Protégé web site]</ref>
 
=== Search ===
 
* [[Swoogle]]
 
== Limitations ==
 
* No direct language support for n-ary relationships. For example modelers may wish to describe the qualities of a relation, to relate more than 2 individuals or to relate an individual to a list. This cannot be done within OWL. They may need to adopt a pattern instead which encodes the meaning outside the formal semantics.<ref>{{cite web |url=http://www.w3.org/TR/swbp-n-aryRelations/ |title=Defining N-ary Relations on the Semantic Web |first=Natasha |last=Noy |authorlink=Natasha Noy |first2=Alan |last2=Rector |authorlink2=Alan Rector |date=2006-04-12 |publisher=World Wide Web Consortium |accessdate=17 April 2010 }}</ref>
 
== See also ==
* RDF
* [[Agris: International Information System for the Agricultural Sciences and Technology]]
* [[Bossam (software)|Bossam]]: A rule-based OWL reasoner
* [[Common logic]]
* [[FOAF (software)|FOAF]] + [[Description of a Career|DOAC]]
* [[Enterprise Architect Visual Modeling Platform|Enterprise Architect]] [http://www.sparxsystems.com/enterprise_architect_user_guide/9.3/domain_based_models/mdg_technology_for_odm.html MDG Technology for ODM] (ODM supports OWL and RDF modeling)
* [[Geopolitical ontology]]
* [[IDEAS Group]]
* [[Meta-Object Facility|Meta-Object Facility (MOF)]], a different standard for the [[Unified Modeling Language|Unified Modeling Language (UML)]] of the [[Object Management Group|Object Management Group (OMG)]]
* [[Multimedia Web Ontology Language]]
* [[SKOS]]
* [[SSWAP]]: Simple Semantic Web Architecture and Protocol
* [[Website Parse Template]]
 
==References==
{{Reflist|2}}
 
==External links==
* [http://www.cs.ox.ac.uk/people/ian.horrocks/Seminars/ Horrocks, Ian] (2010); [http://semtech2010.semanticuniverse.com/ SemTech 2010] tutorial [http://www.comlab.ox.ac.uk/people/ian.horrocks/Seminars/download/Horrocks_Ian_pt1.pdf part 1] and [http://www.comlab.ox.ac.uk/people/ian.horrocks/Seminars/download/Horrocks_Ian_pt2.pdf part 2] on Description Logics and OWL
* [http://www.semantic-web-book.org/page/ESWC09_Tutorial ESWC09 Tutorial] including an introduction to OWL 2
* [http://www.visualmodeling.com/VisualOWL.htm Visual OWL] Visual Modeling Forum page dedicated to graphic notations for OWL
* [http://www.cs.man.ac.uk/~horrocks/ISWC2003/Tutorial/ Tutorial on OWL] at [http://www.cs.man.ac.uk/ the University of Manchester Computer Science Department]
* [http://www.inf.unibz.it/~franconi/dl/course/ ''Introduction to Description Logics'' DL course] by Enrico Franconi, Faculty of Computer Science, Free University of Bolzano, Italy
* [http://www.co-ode.org/ Cooperative Ontologies (CO-ODE) web site] includes OWL tutorial materials and software.
* [http://diplom.ooyoo.de/ UML2OWL - XSLT scripts to transform UML class diagrams into valid OWL DL ontologies / modelling OWL DL ontologies with UML]
* [http://owlapi.sourceforge.net/ OWL API] API for Using OWL 2, at SourceForge
* [http://rowlex.nc3a.nato.int/ ROWLEX Toolkit] NATO C3 Agency Semantic Interoperability Relaxed OWL Experience Toolkit for .NET
* [http://viziquer.lumii.lv ViziQuer] a tool that allows to browse a SPARQL endpoint ontology and construct SPARQL queries
 
{{Semantic Web}}
{{W3C Standards}}
 
[[Category:World Wide Web Consortium standards]]
[[Category:Resource Description Framework]]
[[Category:School of Computer Science, University of Manchester]]
[[Category:XML-based standards]]
[[Category:Declarative programming languages]]
[[Category:Ontology languages]]
[[Category:Semantic Web]]
 
[[ca:OWL]]
[[da:Web Ontology Language]]
[[de:Web Ontology Language]]
[[es:OWL]]
[[eu:OWL]]
[[fa:زبان هستی‌شناسی وب]]
[[fr:Web Ontology Language]]
[[it:Web Ontology Language]]
[[hu:Web Ontology Language]]
[[nl:Web Ontology Language]]
[[ja:OWL]]
[[pl:Web Ontology Language]]
[[pt:OWL]]
[[ru:Web Ontology Language]]
[[fi:OWL]]
[[th:Web Ontology Language]]
[[tr:Web Ontoloji Dili]]
[[uk:Web Ontology Language]]
[[zh:网络本体语言]]

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