OWL 2 Web Ontology Language:
XML Serialization

W3C Editor's Draft 29 September 2008

This version:

http://www.w3.org/2007/OWL/draft/ED-owl2-xml-serialization-20080929/

Latest editor's draft:

http://www.w3.org/2007/OWL/draft/owl2-xml-serialization/

Previous version:

http://www.w3.org/2007/OWL/draft/ED-owl2-xml-serialization-20080922/ (color-coded diff)

Authors:

Bernardo Cuenca Grau, Oxford University

Boris Motik, Oxford University

Peter Patel-Schneider, Bell Labs Research

Contributors:

Sean Bechhofer, The University of Manchester

Ian Horrocks, Oxford University

Bijan Parsia, The University of Manchester

---

Copyright © 2008 W3C^® (MIT, ERCIM, Keio), All Rights Reserved. W3C liability, trademark and document use rules apply.

Abstract

Status of this Document

May Be Superseded

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.

Set of Documents

This document is being published as one of a set of 7 documents:

1. Structural Specification and Functional-Style Syntax
2. Direct Semantics
3. RDF-Based Semantics
4. Mapping to RDF Graphs
5. XML Serialization (this document)
6. Profiles
7. Conformance and Test Cases

Please Comment By ASAP

The OWL Working Group seeks public feedback on these Working Drafts. Please send your comments to public-owl-comments@w3.org (public archive). If possible, please offer specific changes to the text that would address your concern. You may also wish to check the Wiki Version of this document for internal-review comments and changes being drafted which may address your concerns.

No Endorsement

Publication as a Working Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

Patents

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

This document defines an XML syntax for OWL 2, which mirrors the structural specification of OWL 2 [OWL 2 Specification].

The italicized keywords MUST, MUST NOT, SHOULD, SHOULD NOT, and MAY specify certain aspects of the normative behavior of OWL 2 tools, and are interpreted as specified in RFC 2119 [RFC 2119].

The syntax is defined by means of an XML schema [XML Schema], which is available as part of this document. The XML schema has been obtained by a straightforward translation of the structural specification of the OWL 2 Specification [OWL 2 Specification] 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 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.

The local parts of the names used in the XML Schema are the same as the names of their corresponding UML classes.

The XML schema thus captures the structure of OWL 2 entities, expressions, and axioms. Certain global conditions on OWL 2 ontologies, such as the ones described in Sections 5.9.1 and 10 of the OWL 2 Specification [OWL 2 Specification], cannot be captured in an XML schema. Tools parsing OWL 2 ontologies in this syntax need to additionally implement these global conditions.

As the XML syntax corresponds most closely to the structural specification of OWL 2 it is fully typed. It thus differs somewhat from the functional-style syntax of OWL 2 [OWL 2 Specification]. For example, whereas the functional-style syntax uses a nonterminal SomeValuesFrom for existential restrictions on both the object and data properties, the XML syntax provides two elements ox:ObjectSomeValuesFrom and ox:DataSomeValuesFrom.

Each axiom in the OWL 2 XML syntax contains complete information about the type of all the entities in it. Therefore the OWL 2 XML Syntax can be parsed more easily than by using the canonical parsing process from Section 5.9.3 of OWL 2 Specification [OWL 2 Specification]. Nonetheless, each OWL 2 ontology written in the OWL 2 XML syntax MUST satisfy the requirements on declarations and typing from Section 5.9 of the OWL 2 Specification [OWL 2 Specification] that is, declarations for ontology entities MUST be present in the import closure of the ontology as required even if the type of ontology elements can be inferred from the axioms.

Relative URIs in an OWL 2 ontology written in XML syntax MUST be resolved as specified in the XML Base specification [XML Base]. If present, the xml:base on the ox:Ontology element MAY, but need not, be equal to the ontology and/or the version URI of the ontology. The ontology URI and the version URI, even if present, do not participate in the resolution of relative URIs. The expansion of relative URIs using xml:base is handled at the XML level during parsing, and is thus completely independent of the ontology and version URIs of the ontology being parsed.

The XML schema presented here covers the entire OWL 2 structural specification, and thus includes all the features available in OWL 2 profiles [OWL 2 Profiles]. There are no separate schemata for these profiles that is, ontologies that can be expressed by the profiles MUST be written using the most general schema. Validating whether an ontology belongs to a particular profile is not intended to be performed using XML schema mechanisms, so the specification of such mechanisms is beyond the scope of this document.

<xsd:schema 
 xmlns:xsd="http://www.w3.org/2001/XMLSchema"
 xmlns:ox="http://www.w3.org/ns/owl2-xml"
 targetNamespace="http://www.w3.org/ns/owl2-xml"
 elementFormDefault="qualified" attributeFormDefault="qualified">

<xsd:import namespace="http://www.w3.org/XML/1998/namespace" schemaLocation="http://www.w3.org/2001/xml.xsd"/>

<!-- The ontology -->
  
<xsd:element name="Import">
  <xsd:complexType>
    <xsd:simpleContent>
      <xsd:extension base="xsd:anyURI">
        <xsd:attributeGroup ref="xml:specialAttrs"/>
      </xsd:extension>
    </xsd:simpleContent>
  </xsd:complexType>
</xsd:element>

<xsd:element name="Ontology">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:element ref="ox:Import" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:Axiom" minOccurs="0" maxOccurs="unbounded"/>
    </xsd:sequence>
    <xsd:attribute name="ontologyURI" type="xsd:anyURI" use="optional"/>
    <xsd:attribute name="versionURI" type="xsd:anyURI" use="optional"/>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<!-- Entities, anonymous individuals, and literals -->

<xsd:group name="Entity">
  <xsd:choice>
    <xsd:element ref="ox:Class"/>
    <xsd:element ref="ox:Datatype"/>
    <xsd:element ref="ox:ObjectProperty"/>
    <xsd:element ref="ox:DataProperty"/>
    <xsd:element ref="ox:AnnotationProperty"/>
    <xsd:element ref="ox:NamedIndividual"/>
  </xsd:choice>
</xsd:group>

<xsd:element name="Class">
  <xsd:complexType>
    <xsd:attribute name="URI" type="xsd:anyURI" use="required"/>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="Datatype">
  <xsd:complexType>
    <xsd:attribute name="URI" type="xsd:anyURI" use="required"/>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>
 
<xsd:element name="ObjectProperty">
  <xsd:complexType>
    <xsd:attribute name="URI" type="xsd:anyURI" use="required"/>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="DataProperty">
  <xsd:complexType>
    <xsd:attribute name="URI" type="xsd:anyURI" use="required"/>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="AnnotationProperty">
  <xsd:complexType>
    <xsd:attribute name="URI" type="xsd:anyURI" use="required"/>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:group name="Individual">
  <xsd:choice>
    <xsd:element ref="ox:NamedIndividual"/>
    <xsd:element ref="ox:AnonymousIndividual"/>
  </xsd:choice>
</xsd:group>
  
<xsd:element name="NamedIndividual">
  <xsd:complexType>
    <xsd:attribute name="URI" type="xsd:anyURI" use="required"/>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="AnonymousIndividual">
  <xsd:complexType>
    <xsd:attribute name="nodeID" type="xsd:NCName" use="required"/>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="Literal">
 <xsd:complexType>
   <xsd:simpleContent>
     <xsd:extension base="xsd:string">
       <xsd:attribute name="datatypeURI" type="xsd:anyURI"/>
       <xsd:attributeGroup ref="xml:specialAttrs"/>
     </xsd:extension>
   </xsd:simpleContent>
 </xsd:complexType>
</xsd:element>

<!-- Declarations -->

<xsd:element name="Declaration">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:Entity"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>
  
<!-- Object property expressions -->

<xsd:group name="ObjectPropertyExpression">
  <xsd:choice>
    <xsd:element ref="ox:ObjectProperty"/>
    <xsd:element ref="ox:InverseObjectProperty"/>
  </xsd:choice>
</xsd:group>

<xsd:element name="InverseObjectProperty">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:element ref="ox:ObjectProperty"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<!-- Data property expressions -->

<xsd:group name="DataPropertyExpression">
  <xsd:sequence>
    <xsd:element ref="ox:DataProperty"/>
  </xsd:sequence>
</xsd:group>

<!-- Data ranges -->

<xsd:group name="DataRange">
  <xsd:choice>
    <xsd:element ref="ox:Datatype"/>
    <xsd:element ref="ox:DataComplementOf"/>
    <xsd:element ref="ox:DataOneOf"/>
    <xsd:element ref="ox:DatatypeRestriction"/>
  </xsd:choice>
</xsd:group>

<xsd:element name="DataComplementOf">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:DataRange"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="DataOneOf">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:element ref="ox:Literal" minOccurs="1" maxOccurs="unbounded"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="DatatypeRestriction">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:element ref="ox:Datatype"/>
      <xsd:element name="FacetRestriction" minOccurs="1" maxOccurs="unbounded">
        <xsd:complexType>
          <xsd:sequence>
            <xsd:element ref="ox:Literal"/>
          </xsd:sequence>
          <xsd:attribute name="facet" type="xsd:anyURI" use="required"/>
        </xsd:complexType>
      </xsd:element>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<!-- Class expressions -->

<xsd:group name="ClassExpression">
  <xsd:choice>
    <xsd:element ref="ox:Class"/>
    <xsd:element ref="ox:ObjectIntersectionOf"/>
    <xsd:element ref="ox:ObjectUnionOf"/>
    <xsd:element ref="ox:ObjectComplementOf"/>
    <xsd:element ref="ox:ObjectOneOf"/>
    <xsd:element ref="ox:ObjectSomeValuesFrom"/>
    <xsd:element ref="ox:ObjectAllValuesFrom"/>
    <xsd:element ref="ox:ObjectHasValue"/>
    <xsd:element ref="ox:ObjectExistsSelf"/>
    <xsd:element ref="ox:ObjectMinCardinality"/>
    <xsd:element ref="ox:ObjectMaxCardinality"/>
    <xsd:element ref="ox:ObjectExactCardinality"/>
    <xsd:element ref="ox:DataSomeValuesFrom"/>
    <xsd:element ref="ox:DataAllValuesFrom"/>
    <xsd:element ref="ox:DataHasValue"/>
    <xsd:element ref="ox:DataMinCardinality"/>
    <xsd:element ref="ox:DataMaxCardinality"/>
    <xsd:element ref="ox:DataExactCardinality"/>
  </xsd:choice>
</xsd:group>

<xsd:element name="ObjectIntersectionOf">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:ClassExpression" minOccurs="2" maxOccurs="unbounded"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="ObjectUnionOf">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:ClassExpression" minOccurs="2" maxOccurs="unbounded"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="ObjectComplementOf">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:ClassExpression"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="ObjectOneOf">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Individual" minOccurs="1" maxOccurs="unbounded"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="ObjectSomeValuesFrom">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:ObjectPropertyExpression"/>
      <xsd:group ref="ox:ClassExpression"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="ObjectAllValuesFrom">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:ObjectPropertyExpression"/>
      <xsd:group ref="ox:ClassExpression"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="ObjectHasValue">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:ObjectPropertyExpression"/>
      <xsd:group ref="ox:Individual"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="ObjectExistsSelf">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:ObjectPropertyExpression"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="ObjectMinCardinality">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:ObjectPropertyExpression"/>
      <xsd:group ref="ox:ClassExpression" minOccurs="0" maxOccurs="1"/>
    </xsd:sequence>
    <xsd:attribute name="cardinality" type="xsd:nonNegativeInteger" use="required"/>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="ObjectMaxCardinality">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:ObjectPropertyExpression"/>
      <xsd:group ref="ox:ClassExpression" minOccurs="0" maxOccurs="1"/>
    </xsd:sequence>
    <xsd:attribute name="cardinality" type="xsd:nonNegativeInteger" use="required"/>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="ObjectExactCardinality">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:ObjectPropertyExpression"/>
      <xsd:group ref="ox:ClassExpression" minOccurs="0" maxOccurs="1"/>
    </xsd:sequence>
    <xsd:attribute name="cardinality" type="xsd:nonNegativeInteger" use="required"/>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="DataSomeValuesFrom">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:DataPropertyExpression" minOccurs="1" maxOccurs="unbounded"/>
      <xsd:group ref="ox:DataRange"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="DataAllValuesFrom">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:DataPropertyExpression" minOccurs="1" maxOccurs="unbounded"/>
      <xsd:group ref="ox:DataRange"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="DataHasValue">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:DataPropertyExpression"/>
      <xsd:element ref="ox:Literal"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="DataMinCardinality">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:DataPropertyExpression"/>
      <xsd:group ref="ox:DataRange" minOccurs="0" maxOccurs="1"/>
    </xsd:sequence>
    <xsd:attribute name="cardinality" type="xsd:nonNegativeInteger" use="required"/>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="DataMaxCardinality">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:DataPropertyExpression"/>
      <xsd:group ref="ox:DataRange" minOccurs="0" maxOccurs="1"/>
    </xsd:sequence>
    <xsd:attribute name="cardinality" type="xsd:nonNegativeInteger" use="required"/>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="DataExactCardinality">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:DataPropertyExpression"/>
      <xsd:group ref="ox:DataRange" minOccurs="0" maxOccurs="1"/>
    </xsd:sequence>
    <xsd:attribute name="cardinality" type="xsd:nonNegativeInteger" use="required"/>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<!-- Axioms -->

<xsd:group name="Axiom">
  <xsd:choice>
    <xsd:element ref="ox:Declaration"/>
    <xsd:group ref="ox:ClassAxiom"/>
    <xsd:group ref="ox:ObjectPropertyAxiom"/>
    <xsd:group ref="ox:DataPropertyAxiom"/>
    <xsd:element ref="ox:HasKey"/>
    <xsd:group ref="ox:Assertion"/>
    <xsd:element ref="ox:EntityAnnotation"/>
    <xsd:element ref="ox:AnonymousIndividualAnnotation"/>
  </xsd:choice>
</xsd:group>

<!-- Class expression axioms -->

<xsd:group name="ClassAxiom">
  <xsd:choice>
    <xsd:element ref="ox:SubClassOf"/>
    <xsd:element ref="ox:EquivalentClasses"/>
    <xsd:element ref="ox:DisjointClasses"/>
    <xsd:element ref="ox:DisjointUnion"/>
  </xsd:choice>
</xsd:group>

<xsd:element name="SubClassOf">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:ClassExpression"/> <!-- This is the subexpression -->
      <xsd:group ref="ox:ClassExpression"/>  <!-- This is the superexpression -->
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="EquivalentClasses">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:ClassExpression" minOccurs="2" maxOccurs="unbounded"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="DisjointClasses">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:ClassExpression" minOccurs="2" maxOccurs="unbounded"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="DisjointUnion">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:element ref="ox:Class"/>
      <xsd:group ref="ox:ClassExpression" minOccurs="2" maxOccurs="unbounded"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<!-- Object property axioms -->

<xsd:group name="ObjectPropertyAxiom">
  <xsd:choice>
    <xsd:element ref="ox:SubObjectPropertyOf"/>
    <xsd:element ref="ox:EquivalentObjectProperties"/>
    <xsd:element ref="ox:DisjointObjectProperties"/>
    <xsd:element ref="ox:InverseObjectProperties"/>
    <xsd:element ref="ox:ObjectPropertyDomain"/>
    <xsd:element ref="ox:ObjectPropertyRange"/>
    <xsd:element ref="ox:FunctionalObjectProperty"/>
    <xsd:element ref="ox:InverseFunctionalObjectProperty"/>
    <xsd:element ref="ox:ReflexiveObjectProperty"/>
    <xsd:element ref="ox:IrreflexiveObjectProperty"/>
    <xsd:element ref="ox:SymmetricObjectProperty"/>
    <xsd:element ref="ox:AsymmetricObjectProperty"/>
    <xsd:element ref="ox:TransitiveObjectProperty"/>
  </xsd:choice>
</xsd:group>

<xsd:element name="SubObjectPropertyOf">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:choice> <!-- This is the subproperty expression or the property chain -->
        <xsd:group ref="ox:ObjectPropertyExpression"/>
        <xsd:element name="PropertyChain">
          <xsd:complexType>
            <xsd:sequence>
              <xsd:group ref="ox:ObjectPropertyExpression" minOccurs="2" maxOccurs="unbounded"/>
            </xsd:sequence>
            <xsd:attributeGroup ref="xml:specialAttrs"/>
          </xsd:complexType>
        </xsd:element>
      </xsd:choice>
      <xsd:group ref="ox:ObjectPropertyExpression"/> <!-- This is the superproperty expression -->  
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="EquivalentObjectProperties">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:ObjectPropertyExpression" minOccurs="2" maxOccurs="unbounded"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="DisjointObjectProperties">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:ObjectPropertyExpression" minOccurs="2" maxOccurs="unbounded"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="ObjectPropertyDomain">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:ObjectPropertyExpression"/>
      <xsd:group ref="ox:ClassExpression"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="ObjectPropertyRange">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:ObjectPropertyExpression"/>
      <xsd:group ref="ox:ClassExpression"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="InverseObjectProperties">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:ObjectPropertyExpression" minOccurs="2" maxOccurs="2"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="FunctionalObjectProperty">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:ObjectPropertyExpression"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="InverseFunctionalObjectProperty">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:ObjectPropertyExpression"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="ReflexiveObjectProperty">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:ObjectPropertyExpression"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="IrreflexiveObjectProperty">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:ObjectPropertyExpression"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="SymmetricObjectProperty">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:ObjectPropertyExpression"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="AsymmetricObjectProperty">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:ObjectPropertyExpression"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>
 
<xsd:element name="TransitiveObjectProperty">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:ObjectPropertyExpression"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<!-- Data property axioms -->

<xsd:group name="DataPropertyAxiom">
  <xsd:choice>
    <xsd:element ref="ox:SubDataPropertyOf"/>
    <xsd:element ref="ox:EquivalentDataProperties"/>
    <xsd:element ref="ox:DisjointDataProperties"/>
    <xsd:element ref="ox:DataPropertyDomain"/>
    <xsd:element ref="ox:DataPropertyRange"/>
    <xsd:element ref="ox:FunctionalDataProperty"/>
  </xsd:choice>
</xsd:group>

<xsd:element name="SubDataPropertyOf">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:DataPropertyExpression"/> <!-- This is the subproperty expression -->
      <xsd:group ref="ox:DataPropertyExpression"/>  <!-- This is the superproperty expression -->
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="EquivalentDataProperties">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:DataPropertyExpression" minOccurs="2" maxOccurs="unbounded"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="DisjointDataProperties">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:DataPropertyExpression" minOccurs="2" maxOccurs="unbounded"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="DataPropertyDomain">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:DataPropertyExpression"/>
      <xsd:group ref="ox:ClassExpression"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="DataPropertyRange">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:DataPropertyExpression"/>
      <xsd:group ref="ox:DataRange"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="FunctionalDataProperty">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:DataPropertyExpression"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<!-- Key axioms -->

<xsd:element name="HasKey">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:ClassExpression"/>
      <xsd:choice minOccurs="1" maxOccurs="unbounded">
        <xsd:group ref="ox:ObjectPropertyExpression"/>
        <xsd:group ref="ox:DataPropertyExpression"/>
      </xsd:choice>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<!-- Assertions -->

<xsd:group name="Assertion">
  <xsd:choice>
    <xsd:element ref="ox:SameIndividual"/>
    <xsd:element ref="ox:DifferentIndividuals"/>
    <xsd:element ref="ox:ClassAssertion"/>
    <xsd:element ref="ox:ObjectPropertyAssertion"/>
    <xsd:element ref="ox:NegativeObjectPropertyAssertion"/>
    <xsd:element ref="ox:DataPropertyAssertion"/>
    <xsd:element ref="ox:NegativeDataPropertyAssertion"/>
  </xsd:choice>
</xsd:group> 

<xsd:element name="SameIndividual">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:Individual" minOccurs="2" maxOccurs="unbounded"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="DifferentIndividuals">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:Individual" minOccurs="2" maxOccurs="unbounded"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="ClassAssertion">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:ClassExpression"/>
      <xsd:group ref="ox:Individual"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="ObjectPropertyAssertion">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:ObjectPropertyExpression"/>
      <xsd:group ref="ox:Individual"/> <!-- This is the source invididual  -->
      <xsd:group ref="ox:Individual"/> <!--  This is the target individual -->
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="NegativeObjectPropertyAssertion">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:ObjectPropertyExpression"/>
      <xsd:group ref="ox:Individual"/> <!-- This is the source invididual  -->
      <xsd:group ref="ox:Individual"/> <!--  This is the target individual -->
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="DataPropertyAssertion">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:DataPropertyExpression"/>
      <xsd:group ref="ox:Individual"/> <!-- This is the source invididual  -->
      <xsd:element ref="ox:Literal"/> <!--  This is the target value -->
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="NegativeDataPropertyAssertion">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:group ref="ox:DataPropertyExpression"/>
      <xsd:group ref="ox:Individual"/> <!-- This is the source invididual  -->
      <xsd:element ref="ox:Literal"/> <!--  This is the target value -->
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<!-- Annotations  -->

<xsd:element name="Annotation">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:element ref="ox:AnnotationProperty"/>
      <xsd:choice>
        <xsd:group ref="ox:Entity"/>
        <xsd:element ref="ox:AnonymousIndividual"/>
        <xsd:element ref="ox:Literal"/>
      </xsd:choice>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="Label">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:element ref="ox:Literal"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="Comment">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
      <xsd:element ref="ox:Literal"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="Deprecation">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/>
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:group name="Annotation">
  <xsd:choice>
     <xsd:element ref="ox:Annotation"/>
     <xsd:element ref="ox:Label"/>
     <xsd:element ref="ox:Comment"/>
     <xsd:element ref="ox:Deprecation"/>
  </xsd:choice>
</xsd:group>

<!-- Annotation axioms -->

<xsd:element name="EntityAnnotation">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/> <!-- This is the annotation for the axiom -->
      <xsd:group ref="ox:Entity"/>
      <xsd:group ref="ox:Annotation" minOccurs="1" maxOccurs="unbounded"/> <!-- This is the annotation for the entity -->
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

<xsd:element name="AnonymousIndividualAnnotation">
  <xsd:complexType>
    <xsd:sequence>
      <xsd:group ref="ox:Annotation" minOccurs="0" maxOccurs="unbounded"/> <!-- This is the annotation for the axiom -->
      <xsd:element ref="ox:AnonymousIndividual"/>
      <xsd:group ref="ox:Annotation" minOccurs="1" maxOccurs="unbounded"/> <!-- This is the annotation for the anonymous individual -->
    </xsd:sequence>
    <xsd:attributeGroup ref="xml:specialAttrs"/>
  </xsd:complexType>
</xsd:element>

</xsd:schema>

[OWL 2 Primer]

OWL 2 Web Ontology Language: Primer. Bijan Parsia and Peter F. Patel-Schneider, eds., 2008.

[OWL 2 Specification]

OWL 2 Web Ontology Language:Structural Specification and Functional-Style Syntax Boris Motik, Peter F. Patel-Schneider, Ian Horrocks. W3C Editor's Draft, 29 September 2008, http://www.w3.org/2007/OWL/draft/ED-owl2-syntax-20080929/. Latest version available at http://www.w3.org/2007/OWL/draft/owl2-syntax/.

[OWL 2 Profiles]

OWL 2 Web Ontology Language:Profiles Bernardo Cuenca Grau, Boris Motik, Zhe Wu, Achille Fokoue, Carsten Lutz. W3C Editor's Draft, 29 September 2008, http://www.w3.org/2007/OWL/draft/ED-owl2-profiles-20080929/. Latest version available at http://www.w3.org/2007/OWL/draft/owl2-profiles/.

[XML Base]

XML Base. Jonathan Marsh, ed. W3C Recommendation 27 June 2001.

[XML Schema]

XML Schema Part 1: Structures Second Edition. Henry S. Thompson, David Beech, Murray Maloney, and Noah Mendelsohn, eds. W3C Recommendation 28 October 2004.

[RFC 2119]

RFC 2119: Key words for use in RFCs to Indicate Requirement Levels. Network Working Group, S. Bradner. Internet Best Current Practice, March 1997.