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__NUMBEREDHEADINGS__
{{TR|title=XML Serialization}}
<div id='editors'>
; Editors:
: [http://www.cs.ox.ac.uk/people/boris.motik/ Boris Motik], University of Oxford
: [http://www.cs.man.ac.uk/~bparsia/ Bijan Parsia], University of Manchester
: Peter F. Patel-Schneider, Nuance Communications
; Contributors (alphabetical order):
: [http://www.cs.man.ac.uk/~seanb/ Sean Bechhofer], University of Manchester
: [http://www.cs.ox.ac.uk/people/bernardo.cuencagrau/ Bernardo Cuenca Grau], University of Oxford
: [http://domino.research.ibm.com/comm/research_people.nsf/pages/achille.index.html Achille Fokoue], IBM Corporation
: [http://www.leibnizcenter.org/~hoekstra/ Rinke Hoekstra], University of Amsterdam
</div>
; Abstract:
: <div id='abstract'><p>{{:Shared_Abstract}}</p><p>This document specifies an XML serialization for OWL 2 that mirrors its structural specification.  An XML schema defines this syntax and is available as a separate document, as well as being included here.</p></div>
; Status of this Document:

{{:Shared_Copyright}}

<div id='docbody'>

__TOC__

== Overview ==

This document defines the XML serialization for OWL 2, an alternative exchange
syntax for OWL 2 designed for use by XML tools (e.g., tools using, for
example, XQuery [XQuery]).  Although the XML serialization is designed as an
exchange syntax for OWL 2, RDF/XML is the only required exchange syntax
for OWL---use of the XML serialization by OWL 2 tools is optional.

{{:Shared_RFC2119}}

The XML serialization mirrors the structural specification of OWL 2 [<cite>[[#ref-owl-2-specification|OWL 2 Specification]]</cite>] and is defined by means of an XML schema [<cite>[[#ref-xml-schema|XML Schema]]</cite>] plus some additional constraints in prose.

The elements in the XML Schema belong to the ''<nowiki>&lt;http://www.w3.org/2002/07/owl#&gt;</nowiki>'' namespace, and the attributes belong to no namespace. The local parts of the names used in the XML Schema are the same as the names of their corresponding elements from the structural specification. Thus, the XML serialization can be seen as a 
notational variant of the functional syntax.

As a notational variant of the functional syntax, every OWL 2 ontology serialized according to this specification can also be serialized as an RDF document in a suitable concrete syntax such as RDF/XML. A suitable XSLT stylesheet, along with GRDDL, can allow GRDDL aware software to treat documents serialized as OWL/XML as if they were serialized as RDF/XML. See [http://www.w3.org/2009/owl-xgx/ OWL-XGX] for an informative example of how this works.

== Example Ontology (Informative) ==

<div class="anexample">
The following is an example of an OWL 2 ontology written in the XML serialization.

More examples can be found in the OWL 2 Primer [<cite>[[#ref-owl-2-primer|OWL 2 Primer]]</cite>].

<div class="xmlsyn">
<pre><?xml version="1.0" encoding="UTF-8"?>
<Ontology xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.w3.org/2002/07/owl# http://www.w3.org/2009/09/owl2-xml.xsd"
    xmlns="http://www.w3.org/2002/07/owl#"
    xml:base="http://example.com/myOntology"
    ontologyIRI="http://example.com/myOntology">
    
    <Prefix name="myOnt" IRI="http://example.com/myOntology#"/>
    <Import>http://example.com/someOtherOntology</Import>

    <Declaration>
        <Class IRI="#Animal"/>
    </Declaration>
    <Declaration>
        <Class abbreviatedIRI="myOnt:Tabloid"/>
    </Declaration>
    <Declaration>
        <ObjectProperty IRI="#eats"/>
    </Declaration>
    <Declaration>
        <ObjectProperty IRI="#reads"/>
    </Declaration>

    <SubClassOf>
        <Class abbreviatedIRI="myOnt:Animal"/>
        <ObjectAllValuesFrom>
            <ObjectProperty IRI="#reads"/>
            <Class IRI="#Tabloid"/>
        </ObjectAllValuesFrom>
    </SubClassOf>

</Ontology>
</pre>
</div>
</div>

== The Serialization Syntax  ==

=== IRIs ===
During parsing of ontology documents written in the XML serialization of OWL 2, all values that are declared in the schema given below as being of type ''xsd:anyURI'' <em title="MUST in RFC 2119 context" class="RFC2119">MUST</em> be resolved against the respective ''base IRI'' as specified in the XML Base specification [<cite>[[#ref-xml-base|XML Base]]</cite>].

In contrast, OWL 2 literals of the ''xsd:anyURI'' datatype <em title="MUST NOT in RFC 2119 context" class="RFC2119">MUST NOT</em> be resolved against the base IRI: all literals of OWL 2 are treated as opaque values whose value is fully defined by their lexical representation (as described in [[Syntax#IRIs_2|Section 4.6]] of the <cite>[[#ref-owl-2-specification|OWL 2 Specification]]</cite>]).

Ontology documents written in the XML serialization of OWL 2 may make use of
abbreviated IRIs as described in [[Syntax#IRIs|Section 2.4]] of the <cite>[[#ref-owl-2-specification|OWL 2 Specification]]</cite>]. Such ontology
documents <em title="MUST in RFC 2119 context" class="RFC2119">MUST</em> declare
all prefixes used in the values of ''abbreviatedIRI'' attributes using a ''Prefix'' element in that document. In any particular file, a prefix may be defined by only one Prefix element and prefix declarations are scoped to
the file in which they lexically appear. Thus, prefix declarations are not imported.

On any element, one, and exactly one, of an ''IRI'' attribute or an ''abbreviatedIRI'' attribute <em title="MUST in RFC 2119 context" class="RFC2119">MUST</em>  appear. This constraint is not expressed in the Schema for technical reasons.

During parsing of ontology documents written in the XML serialization of OWL 2, 
every ''abbreviatedIRI'' attribute  <em title="MUST in RFC 2119 context" class="RFC2119">MUST</em> be replaced with a corresponding
''IRI'' attribute. The value of the ''abbreviatedIRI'' attribute  <em title="MUST in RFC 2119 context" class="RFC2119">MUST</em> be
expanded into a full IRI as described in [[Syntax#IRIs|Section 2.4]] of the [<cite>[[#ref-owl-2-specification|OWL 2 Specification]]</cite>].

Note: The structural specification does not handle either relative IRIs or abbreviated IRIs and their attendant syntax. Thus, an API which exactly
conforms to the structural syntax can handle only absolute IRIs as the 
identifier for OWL entities. However, implementations are free to use whatever
internal representation they see fit. An implementation based on the XML DOM [<cite>[[#ref-dom|Document Object Model]]</cite>] could sensibly choose to maintain the abbreviated IRI machinery so
long as it also exposed an API which presented all corresponding expanded IRIs.

=== Imports and Global Conditions ===

OWL imports are not handled at the XML level, but must be handled separately.

An OWL 2 ontology written in the XML serialization of OWL 2 <em
title="MUST in RFC 2119 context" class="RFC2119">MUST</em> satisfy the
conditions on OWL 2 ontologies from Section 3 of the OWL 2 Specification
[<cite>[[#ref-owl-2-specification|OWL 2 Specification]]</cite>].

An OWL 2 DL ontology written in the XML serialization of OWL 2 <em
title="MUST in RFC 2119 context" class="RFC2119">MUST</em> satisfy the
conditions on OWL 2 DL ontologies from Section 3 of the OWL 2
Specification [<cite>[[#ref-owl-2-specification|OWL 2
Specification]]</cite>].  Some of these conditions involve imported
ontologies, thus it is possible for an OWL 2 DL ontology written in the
XML serialization of OWL 2 to satisfy the conditions to be an OWL 2 DL
ontology in a manner invisible to XML Schema checking tools since they
are not sensitive to OWL imports.

=== Profiles ===

The XML schema presented here covers the entire OWL 2 structural specification, and thus includes all the features available in OWL 2 profiles [<cite>[[#ref-owl-2-profiles|OWL 2 Profiles]]</cite>].

=== The XML Schema ===

This schema may also be [http://www.w3.org/2009/09/owl2-xml.xsd downloaded directly].

{{:OWL_XML_Schema}}

== OWL 2 XML serialization ontology document ==

An ''OWL 2 XML serialization ontology document'' is a sequence of Unicode [<cite>[[#ref-unicode|UNICODE]]</cite>] characters accessible from some IRI by means of the standard protocols that can be parsed into an XML document that conforms to the XML schema defined in this document and adheres to the constraints described in [[#The_Serialization_Syntax|Section 3]] of this document.

== Appendix: The Derivation from the Functional Syntax (Informative) ==

The XML schema has been obtained by a straightforward
translation of the structural specification of the OWL 2 Specification [<cite>[[#ref-owl-2-specification|OWL 2 Specification]]</cite>] in the following way:

* Each UML class that is intended to be instantiated is mapped to a global element, whose elements and attributes correspond to the components of the UML class. Each such element has an XML Schema type with the same name.
* Each UML class that is not intended to be instantiated directly, but instead gathers together commonalities, is mapped to a global element group, whose choice members correspond to the children of the UML class. For all except a select few, there is a corresponding global, abstract XML Schema type with the same name. The particles in the content model of the group are mapped into the corresponding subtypes of the group type.

Since XML Schema's type system does not support multiple inheritance, some abstract UML classes cannot be directly mapped into an XML Schema type hierarchy with the intended result. In the case where there are multiple parent classes, only the most useful parents are mapped into the active type hierarchy. The excluded groups are:
*Entity
*AnnotationSubject
*AnnotationValue

Some groups are mere documentation in the schema, and therefore are not included as types: 
* axiomAnnotations
* ontologyAnnotations
* annotationAnnotations

The XML schema thus captures the structure of OWL 2 entities, expressions, and axioms. Not all XML documents which are legal according to this schema correspond to structural correct OWL ontologies.

To get to the OWL Ontology an OWL 2 XML serialization ontology document
describes one must:
* Resolve all the IRIs and expand the abbreviated IRIs in the above described way.
* Get the imports closure of the ontology.

To determine whether the OWL Ontology is structurally correct, one must:
* Check the global constraints on axioms.
* Check the typing constraints.

Each axiom in the XML syntax of OWL 2 contains complete information about the type of all the entities in it. Therefore the OWL 2 XML Syntax parsing process is simpler than the canonical parsing process from Section 3.6 of OWL 2 Specification [<cite>[[#ref-owl-2-specification|OWL 2 Specification]]</cite>].

== Appendix: Internet Media Type, File Extension, and Macintosh File Type  ==

; Contact:
: Ivan Herman / Sandro Hawke
; See also:
: How to Register a Media Type for a W3C Specification {{:References/cite-register-mime}} and Internet Media Type registration, consistency of use {{:References/cite-mime-consistency}}.

The Internet Media Type / MIME Type for the OWL XML Serialization is <tt>application/owl+xml</tt>.

It is recommended that OWL XML Serialization files have the extension <tt>.owx</tt> (all lowercase) on all platforms.

It is recommended that OWL XML Serialization files stored on Macintosh HFS file systems be given a file type of <tt>TEXT</tt>.

The information that follows will be submitted to the IESG for review, approval, and registration with IANA.

; Type name:
:    application
; Subtype name:
:    owl+xml
; Required parameters:
:   None
; Optional parameters:
:   charset  This parameter may be required when transfering non-ASCII data across some protocols. 
; Encoding considerations:
:    The syntax of the OWL XML Serialization is expressed over code points in Unicode [<cite>[[#ref-unicode|UNICODE]]</cite>]. 
; Security considerations:
:    The OWL XML Serialization uses IRIs as term identifiers. Applications interpreting data expressed in the OWL XML Serialization should address the security issues of Internationalized Resource Identifiers (IRIs) [<cite>[[#ref-rfc-3987|RFC 3987]]</cite>] Section 8, as well as Uniform Resource Identifiers (URI): Generic Syntax [<cite>[[#ref-rfc-3986|RFC 3986]]</cite>] Section 7. Multiple IRIs may have the same appearance. Characters in different scripts may look similar (a Cyrillic "o" may appear similar to a Latin "o"). A character followed by combining characters may have the same visual representation as another character (LATIN SMALL LETTER E followed by COMBINING ACUTE ACCENT has the same visual representation as LATIN SMALL LETTER E WITH ACUTE). Any person or application that is writing or interpreting data in the OWL XML Serialization must take care to use the IRI that matches the intended semantics, and avoid IRIs that may look similar. Further information about matching of similar characters can be found in Unicode Security Considerations [<cite>[[#ref-unisec|UNISEC]]</cite>] and Internationalized Resource Identifiers (IRIs) [<cite>[[#ref-rfc-3987|RFC 3987]]</cite>] Section 8.
; Interoperability considerations:
:    There are no known interoperability issues.
; Published specification:
:    This specification.
; Applications which use this media type:
:    None at current time.
; Additional information:
:     None.
; Magic number(s):
:    OWL XML documents are XML documents and thus may have initial strings similar to any XML document.
; File extension(s):
:    ".owx"
; Base URI:
:   As in XML.
; Macintosh file type code(s):
:    "TEXT"
; Person & email address to contact for further information:
:    Ivan Herman, ivan@w3.org / Sandro Hawke, sandro@w3.org. Please send technical comments and questions about OWL to public-owl-comments@w3.org, a mailing list with a public archive at http://lists.w3.org/Archives/Public/public-owl-comments/
; Intended usage:
:     COMMON
; Restrictions on usage:
:     None
; Author/Change controller:
:   The OWL XML Serialization is the product of the W3C OWL Working Group; W3C reserves change control over this specification.

<div id="changelog">
== Appendix: Change Log (Informative) ==

=== Changes Since Recommendation ===

This section summarizes the changes to this document since the [http://www.w3.org/TR/2009/REC-owl2-xml-serialization-20091027/ Recommendation of 27 October, 2009].

* With the publication of the XML Schema Definition Language (XSD) 1.1 Part 2: Datatypes [http://www.w3.org/TR/2012/REC-xmlschema11-2-20120405/ Recommendation of 5 April 2012], the elements of OWL 2 which are based on XSD 1.1 are now considered required, and the note detailing the optional dependency on the XSD 1.1 [http://www.w3.org/TR/2009/CR-xmlschema11-2-20090430/ Candidate Recommendation of 30 April, 2009] has been removed from the "Status of this Document" section.
* Minor typographical errors were corrected as detailed on the [http://www.w3.org/2007/OWL/wiki/Errata OWL 2 Errata] page.

=== Changes Since Proposed Recommendation ===

This section summarizes the changes to this document since the [http://www.w3.org/TR/2009/PR-owl2-xml-serialization-20090922/ Proposed Recommendation of 22 September, 2009].

* A note on the use of GRDDL was added to the introduction.
* An editor's note on the future definition of a GRDDL transformation mechanism was removed.
* Some minor editorial changes were made.

=== Changes Since Candidate Recommendation ===

This section summarizes the changes to this document since the [http://www.w3.org/TR/2009/CR-owl2-xml-serialization-20090611/ Candidate Recommendation of 11 June, 2009].
* There were a few bug fixes in the schema itself (see [http://www.w3.org/2007/OWL/wiki/OWL_XML_Schema http://www.w3.org/2007/OWL/wiki/OWL_XML_Schema]).
* Some minor editorial changes were made.

=== Changes Since Last Call ===

This section summarizes the changes to this document since the [http://www.w3.org/TR/2009/WD-owl2-xml-serialization-20090421/ Last Call Working Draft of 21 April, 2009].
* Some minor editorial changes were made.
</div>

== Acknowledgments ==

{{:Shared_Acknowledgments}}
The editors extend special thanks to
Kendall Clark (Clark & Parsia),
Achille Fokoue (IBM Corporation) and
Michael Grove (Clark & Parsia),
Rinke Hoekstra (University of Amsterdam)
for their thorough reviews, to Liam Quim (W3C) for
his advice on XML Schema, and to Dmitry Repchevsky (Barcelona Supercomputing Centre) for catching a bug in the schema.

{{:Regular_attendees}}
{{:Past_Members}}

== References ==

=== Normative References ===

{{:References/ref-grddl}}
{{:References/ref-owl-2-specification}}
{{:References/ref-rfc-2119}}
{{:References/unicode}}
{{:References/ref-xml-base}}
{{:References/ref-xml-schema}}

=== Nonnormative References ===

{{:References/ref-dom}}
{{:References/ref-mime-consistency}}
{{:References/ref-owl-2-primer}}
{{:References/ref-owl-2-profiles}}
{{:References/ref-register-mime}}
{{:References/ref-rfc-3986}}
{{:References/ref-rfc-3987}}
{{:References/ref-unisec}}

</div>
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