Difference between revisions of "Profiles"

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(OWL 2 EL)
(Appendix: Complete Grammars for Profiles)
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=== OWL 2 EL ===
 
=== OWL 2 EL ===
  
The grammar of OWL 2 EL consists of the productions defining the general definitions from [[#General_Definitions|Section 13.1]] of the OWL 2 Specification [<cite>[[#ref-owl-2-specification|OWL 2 Specification]]</cite>], as well as the following productions.
+
The grammar of OWL 2 EL consists of the general definitions from [[#General_Definitions|Section 13.1]] of the OWL 2 Specification [<cite>[[#ref-owl-2-specification|OWL 2 Specification]]</cite>], as well as the following productions.
  
 
<div class="grammar">
 
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=== OWL 2 QL ===
 
=== OWL 2 QL ===
  
The grammar of OWL 2 QL consists of the productions defining the general concepts of the language from the OWL 2 Specification [<cite>[[#ref-owl-2-specification|OWL 2 Specification]]</cite>], as well as the following productions.
+
The grammar of OWL 2 QL consists of the general definitions from [[#General_Definitions|Section 13.1]] of the OWL 2 Specification [<cite>[[#ref-owl-2-specification|OWL 2 Specification]]</cite>], as well as the following productions.
  
 
<div class="grammar">
 
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=== OWL 2 RL ===
 
=== OWL 2 RL ===
  
The grammar of OWL 2 RL consists of the productions defining the general concepts of the language from the OWL 2 Specification [<cite>[[#ref-owl-2-specification|OWL 2 Specification]]</cite>], as well as the following productions.
+
The grammar of OWL 2 RL consists of the general definitions from [[#General_Definitions|Section 13.1]] of the OWL 2 Specification [<cite>[[#ref-owl-2-specification|OWL 2 Specification]]</cite>], as well as the following productions.
  
 
<div class="grammar">
 
<div class="grammar">

Revision as of 11:58, 10 March 2009

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Document title:
OWL 2 Web Ontology Language
Profiles (Second Edition)
Editors
Boris Motik, Oxford University
Bernardo Cuenca Grau, Oxford University
Ian Horrocks, Oxford University
Zhe Wu, Oracle
Achille Fokoue, IBM
Carsten Lutz, University of Bremen
Contributors (alphabetical order)
Diego Calvanese, Free University of Bozen-Bolzano
Jeremy Carroll, TopQuadrant
Giuseppe De Giacomo, Sapienza Università di Roma
Ivan Herman, W3C/ERCIM
Bijan Parsia, University of Manchester
Peter F Patel-Schneider, Bell Labs Research, Alcatel-Lucent
Alan Ruttenberg, Science Commons (Creative Commons)
Abstract
The OWL 2 Web Ontology Language, informally OWL 2, is an ontology language for the Semantic Web with formally defined meaning. OWL 2 ontologies provide classes, properties, individuals, and data values and are stored as Semantic Web documents. OWL 2 ontologies can be used along with information written in RDF, and OWL 2 ontologies themselves are primarily exchanged as RDF documents. The OWL 2 Document Overview describes the overall state of OWL 2, and should be read before other OWL 2 documents.
This document provides a specification of several profiles of OWL 2 which can be more simply and/or efficiently implemented. In logic, profiles are often called fragments. Most profiles are defined by placing restrictions on the structure of OWL 2 ontologies. These restrictions have been specified by modifying the productions of the functional-style syntax.
Status of this Document

Copyright © 2008-2009 W3C® (MIT, ERCIM, Keio), All Rights Reserved. W3C liability, trademark and document use rules apply.

1 Introduction

An OWL 2 profile (commonly called a fragment or a sublanguage in computational logic) is a trimmed down version of OWL 2 that trades some expressive power for the efficiency of reasoning. This document describes three profiles of OWL 2, each of which achieves efficiency in a different way and is useful in different application scenarios. The choice of which profile to use in practice will depend on the structure of the ontologies and the reasoning tasks at hand.

  • OWL 2 EL is particularly useful in applications employing ontologies that contain very large numbers of properties and/or classes. This profile captures the expressive power used by many such ontologies and is a subset of OWL 2 for which the basic reasoning problems can be performed in time that is polynomial with respect to the size of the ontology [EL++]. Dedicated reasoning algorithms for this profile are available and have been demonstrated to be implementable in a highly scalable way.
  • OWL 2 QL is aimed at applications that use very large volumes of instance data, and where query answering is the most important reasoning task. In OWL 2 QL, conjunctive query answering can be implemented using conventional relational database systems. Using a suitable reasoning technique, sound and complete conjunctive query answering can be performed in LOGSPACE with respect to the size of the data (assertions). As in OWL 2 EL, polynomial time algorithms can be used to implement the ontology consistency and class expression subsumption reasoning problems. The expressive power of the profile is necessarily quite limited, although it does include most of the main features of conceptual models such as UML class diagrams and ER diagrams.
  • OWL 2 RL is aimed at applications that require scalable reasoning without sacrificing too much expressive power. It is designed to accommodate OWL 2 applications that can trade the full expressivity of the language for efficiency, as well as RDF(S) applications that need some added expressivity. OWL 2 RL reasoning systems can be implemented using rule-based reasoning engines. The ontology consistency, class expression satisfiability, class expression subsumption, instance checking, and conjunctive query answering problems can be solved in time that is polynomial with respect to the size of the ontology.

OWL 2 profiles are defined by placing restrictions on the structure of OWL 2 ontologies. Syntactic restrictions can be specified by modifying the grammar of the functional-style syntax [OWL 2 Specification] and possibly giving additional global restrictions. In this document, the modified grammars are specified in two ways. In each profile definition, only the difference with respect to the full grammar is given; that is, only the productions that differ from the functional-style syntax are presented, while the productions that are the same as in the functional-style syntax are not repeated. Furthermore, the full grammar for each of the profiles is given in the Appendix.

An ontology in any profile can be written into an ontology document by using any of the syntaxes of OWL 2.

Apart from the ones specified here, there are many other possible profiles of OWL 2 — there are, for example, a whole family of profiles that extend OWL 2 QL. This document does not list OWL Lite [OWL 1 Reference]; however, all OWL Lite ontologies are OWL 2 ontologies, so OWL Lite can be viewed as a profile of OWL 2. Similarly, OWL 1 DL can also be viewed as a profile of OWL 2.

The italicized keywords MUST, MUST NOT, SHOULD, SHOULD NOT, and MAY are used to specify normative features of OWL 2 documents and tools, and are interpreted as specified in RFC 2119 [RFC 2119].

Feature At Risk #1: OWL 2 Specification dependency

This document depends on the four features identified in the OWL 2 Specification [OWL 2 Specification] as being at risk. Depending on the resolution of these features, this document will be updated in accordance with the OWL 2 Specification.

Please send feedback to public-owl-comments@w3.org.

2 OWL 2 EL

The OWL 2 EL profile [EL++,EL++ Update] is designed as a subset of OWL 2 that

  • captures the expressive power used by many large-scale ontologies and
  • for which ontology satisfiability, class expression subsumption, and instance checking can be decided in polynomial time.

OWL 2 EL provides class constructors that are sufficient to express many complex ontologies, such as the biomedical ontology SNOMED CT [SNOMED CT].

2.1 Feature Overview

OWL 2 EL places restrictions on the type of class restrictions that can be used in axioms. In particular, the following types of class restrictions are supported:

  • existential quantification to a class expression (ObjectSomeValuesFrom) or a data range (DataSomeValuesFrom)
  • existential quantification to an individual (ObjectHasValue) or a literal (DataHasValue)
  • self-restriction (ObjectHasSelf)
  • enumerations involving a single individual (ObjectOneOf) or a single literal (DataOneOf)
  • intersection of classes (ObjectIntersectionOf) and data ranges (DataIntersectionOf)

OWL 2 EL supports the following axioms, all of which are restricted to the allowed set of class expressions:

  • class inclusion (SubClassOf)
  • class equivalence (EquivalentClasses)
  • class disjointness (DisjointClasses)
  • object property inclusion (SubObjectPropertyOf) with or without property chains, and data property inclusion (SubDataPropertyOf)
  • property equivalence (EquivalentObjectProperties and EquivalentDataProperties),
  • transitive object properties (TransitiveObjectProperty)
  • reflexive object properties (ReflexiveObjectProperty)
  • domain restrictions (ObjectPropertyDomain and DataPropertyDomain)
  • range restrictions (ObjectPropertyRange and DataPropertyRange)
  • assertions (SameIndividual, DifferentIndividuals, ClassAssertion, ObjectPropertyAssertion, DataPropertyAssertion, NegativeObjectPropertyAssertion, and NegativeDataPropertyAssertion)
  • functional data properties (FunctionalDataProperty)
  • keys (HasKey)

The following constructs are not supported in OWL 2 EL:

  • universal quantification to a class expression (ObjectAllValuesFrom) or a data range (DatAllaValuesFrom)
  • cardinality restrictions (ObjectMaxCardinality, ObjectMinCardinality, ObjectExactCardinality, DataMaxCardinality, DataMinCardinality, and DataExactCardinality)
  • disjunction (ObjectUnionOf, DisjointUnion, and DataUnionOf)
  • class negation (ObjectComplementOf)
  • enumerations involving more than one individual (ObjectOneOf and DataOneOf)
  • disjoint properties (DisjointObjectProperties and DisjointDataProperties)
  • irreflexive object properties (IrreflexiveObjectProperty)
  • inverse object properties (InverseObjectProperties)
  • functional and inverse-functional object properties (FunctionalObjectProperty and InverseFunctionalObjectProperty)
  • symmetric object properties (SymmetricObjectProperty)
  • asymmetric object properties (AsymmetricObjectProperty)

2.2 Profile Specification

The following sections specify the structure of OWL 2 EL ontologies.

2.2.1 Entities

Entities are defined in OWL 2 EL in the same way as in the structural specification [OWL 2 Specification], and OWL 2 EL supports all predefined classes and properties. Furthermore, OWL 2 EL supports the following datatypes:

  • rdf:text
  • rdf:XMLLiteral
  • rdfs:Literal
  • owl:real
  • owl:rational
  • xsd:decimal
  • xsd:integer
  • xsd:nonNegativeInteger
  • xsd:string
  • xsd:normalizedString
  • xsd:token
  • xsd:Name
  • xsd:NCName
  • xsd:NMTOKEN
  • xsd:hexBinary
  • xsd:base64Binary
  • xsd:anyURI
  • xsd:dateTimeStamp

The set of supported datatypes has been designed such that the intersection of the value spaces of any set of these datatypes is either empty or infinite, which is necessary to obtain the desired computational properties [EL++]. Consequently, the following datatypes MUST NOT be used in OWL 2 EL: owl:realPlus, xsd:double, xsd:float, xsd:nonPositiveInteger, xsd:positiveInteger, xsd:negativeInteger, xsd:long, xsd:int, xsd:short, xsd:byte, xsd:unsignedLong, xsd:unsignedInt, xsd:unsignedShort, xsd:unsignedByte, xsd:language, and xsd:boolean.

Finally, OWL 2 EL does not support anonymous individuals.

Individual := NamedIndividual

2.2.2 Property Expressions

Inverse properties are not supported in OWL 2 EL, so object property expressions are restricted to named properties. Data property expressions are defined in the same way as in the structural specification [OWL 2 Specification].

ObjectPropertyExpression := ObjectProperty

2.2.3 Class Expressions

In order to allow for efficient reasoning, OWL 2 EL restricts the set of supported class expressions to ObjectIntersectionOf, ObjectSomeValuesFrom, ObjectHasSelf, ObjectHasValue, DataSomeValuesFrom, DataHasValue, and ObjectOneOf containing a single individual.

ClassExpression :=
    Class | ObjectIntersectionOf | ObjectOneOf |
    ObjectSomeValuesFrom | ObjectHasValue | ObjectHasSelf |
    DataSomeValuesFrom | DataHasValue
ObjectOneOf := 'ObjectOneOf' '(' Individual ')'

2.2.4 Data Ranges

A data range expression is restricted in OWL 2 EL to the predefined datatypes admitted in OWL 2 EL, intersections of data ranges, and to enumerations of literals consisting of a single literal.

DataRange := Datatype | DataIntersectionOf | DataOneOf
DataOneOf := 'DataOneOf' '(' Literal ')'

2.2.5 Axioms

The class axioms of OWL 2 EL are the same as in the structural specification [OWL 2 Specification], with the exception that DisjointUnion is disallowed. Different class axioms are defined in the same way as in the structural specification [OWL 2 Specification], with the difference that they use the new definition of ClassExpression.

ClassAxiom := SubClassOf | EquivalentClasses | DisjointClasses

OWL 2 EL supports the following object property axioms, which are defined in the same way as in the structural specification [OWL 2 Specification], with the difference that they use the new definition of ObjectPropertyExpression.

ObjectPropertyAxiom :=
    EquivalentObjectProperties | SubObjectPropertyOf |
    ObjectPropertyDomain | ObjectPropertyRange |
    ReflexiveObjectProperty | TransitiveObjectProperty

OWL 2 EL provides the same axioms about data properties as the structural specification [OWL 2 Specification] apart from DisjointDataProperties.

DataPropertyAxiom :=
    SubDataPropertyOf | EquivalentDataProperties |
    DataPropertyDomain | DataPropertyRange | FunctionalDataProperty

The assertions in OWL 2 EL, as well as all other axioms, are the same as in the structural specification [OWL 2 Specification], with the difference that class object property expressions are restricted as defined in the previous sections.

2.2.6 Global Restrictions

OWL 2 EL extends the global restrictions on axioms from Section 11 of the structural specification [OWL 2 Specification] with an additional condition [EL++ Update]. In order to define this condition, the following notion is used.

The set of axioms Ax imposes a range restriction to a class expression CE on an object property OP1 if Ax contains the following axioms, where k ≥ 1 is an integer and OPi are object properties:

SubObjectPropertyOf( OP1 OP2)
...
SubObjectPropertyOf( OPk-1 OPk )
ObjectPropertyRange( OPk CE )

The axiom closure Ax of an OWL 2 EL ontology MUST obey the restrictions described in Section 11 of the structural specification [OWL 2 Specification] and, in addition, if

  • Ax contains SubObjectPropertyOf( ObjectPropertyChain( OP1 ... OPn ) OP ) and
  • Ax imposes a range restriction to some class expression CE on OP

then Ax MUST impose a range restriction to CE on OPn.

This additional restriction is vacuously true for each SubObjectPropertyOf axiom in which in the first item of the previous definition does not contain a property chain. There are no additional restrictions for range restrictions on reflexive and transitive roles — that is, a range restriction can be placed on a reflexive and/or transitive role provided that it satisfies the previously mentioned restriction.

3 OWL 2 QL

The OWL 2 QL profile admits sound and complete reasoning in LOGSPACE with respect to the size of the data (assertions), while providing many of the main features necessary to express conceptual models such as UML class diagrams and ER diagrams. In particular, this profile contains the intersection of RDFS and OWL 2. It is based on the DL-Lite family of description logics. Several variants of DL-Lite have been described in the literature [DL-Lite], and DL-LiteR provides the logical underpinning for OWL 2 QL. DL-LiteR does not require the unique name assumption (UNA), since making this assumption would have no impact on the semantic consequences of a DL-LiteR ontology. More expressive variants of DL-Lite, such as DL-LiteA, extend DL-LiteR with functional properties, and these can also be extended with keys; however, for query answering to remain in LOGSPACE, these extensions require UNA and need to impose certain global restrictions on the interaction between properties used in different types of axiom. Basing OWL 2 QL on DL-LiteR avoids practical problems involved in the explicit axiomatization of UNA. Other variants of DL-Lite can also be supported on top of OWL 2 QL, but may require additional restrictions on the structure of ontologies [DL-Lite].

3.1 Feature Overview

OWL 2 QL is defined not only in terms of the set of supported constructs, but it also restricts the places in which these constructs are allowed to occur. The allowed usage of constructs in class expressions is summarized in Table 1.

Table 1. Syntactic Restrictions on Class Expressions in OWL 2 QL
Subclass Expressions Superclass Expressions
a class
existential quantification (ObjectSomeValuesFrom)
    where the class is limited to owl:Thing
existential quantification to a data range (DataSomeValuesFrom)
a class
existential quantification to a class (ObjectSomeValuesFrom)
existential quantification to a data range (DataSomeValuesFrom)
negation (ObjectComplementOf)
intersection (ObjectIntersectionOf)

OWL 2 QL supports the following axioms, constrained so as to be compliant with the mentioned restrictions on class expressions:

  • subclass axioms (SubClassOf)
  • class expression equivalence (EquivalentClasses)
  • class expression disjointness (DisjointClasses)
  • inverse object properties (InverseObjectProperties)
  • property inclusion (SubObjectPropertyOf not involving property chains and SubDataPropertyOf)
  • property equivalence (EquivalentObjectProperties and EquivalentDataProperties)
  • property domain (ObjectPropertyDomain and DataPropertyDomain)
  • property range (ObjectPropertyRange and DataPropertyRange)
  • disjoint properties (DisjointObjectProperties and DisjointDataProperties)
  • symmetric properties (SymmetricObjectProperty)
  • assertions other than the equality assertions (DifferentIndividuals, ClassAssertion, ObjectPropertyAssertion, and DataPropertyAssertion)

The following constructs are not supported in OWL 2 QL:

  • existential quantification to a class expression or a data range (ObjectSomeValuesFrom in the subclass position)
  • self-restriction (ObjectHasSelf)
  • existential quantification to an individual or a literal (ObjectHasValue, DataHasValue)
  • enumeration of individuals and literals (ObjectOneOf, DataOneOf)
  • universal quantification to a class expression or a data range (ObjectAllValuesFrom, DataAllValuesFrom)
  • cardinality restrictions (ObjectMaxCardinality, ObjectMinCardinality, ObjectExactCardinality, DataMaxCardinality, DataMinCardinality, DataExactCardinality)
  • disjunction (ObjectUnionOf, DisjointUnion, and DataUnionOf)
  • property inclusions (SubObjectPropertyOf involving property chains)
  • functional and inverse-functional properties (FunctionalObjectProperty, InverseFunctionalObjectProperty, and FunctionalDataProperty)
  • transitive properties (TransitiveObjectProperty)
  • reflexive properties (ReflexiveObjectProperty)
  • irreflexive properties (IrreflexiveObjectProperty)
  • asymmetric properties (AsymmetricObjectProperty)
  • keys (HasKey)

3.2 Profile Specification

The productions for OWL 2 QL are defined in the following sections. Note that each OWL 2 QL ontology must satisfy the global restrictions on axioms defined in Section 11 of the structural specification [OWL 2 Specification].

3.2.1 Entities

Entities are defined in OWL 2 QL in the same way as in the structural specification [OWL 2 Specification], and OWL 2 QL supports all predefined classes and properties. Furthermore, OWL 2 QL supports the following datatypes:

  • rdf:text
  • rdf:XMLLiteral
  • rdfs:Literal
  • owl:real
  • owl:rational
  • xsd:decimal
  • xsd:integer
  • xsd:nonNegativeInteger
  • xsd:string
  • xsd:normalizedString
  • xsd:token
  • xsd:Name
  • xsd:NCName
  • xsd:NMTOKEN
  • xsd:hexBinary
  • xsd:base64Binary
  • xsd:anyURI
  • xsd:dateTimeStamp

The set of supported datatypes has been designed such that the intersection of the value spaces of any set of these datatypes is either empty or infinite, which is necessary to obtain the desired computational properties. Consequently, the following datatypes MUST NOT be used in OWL 2 QL: owl:realPlus, xsd:double, xsd:float, xsd:nonPositiveInteger, xsd:positiveInteger, xsd:negativeInteger, xsd:long, xsd:int, xsd:short, xsd:byte, xsd:unsignedLong, xsd:unsignedInt, xsd:unsignedShort, xsd:unsignedByte, xsd:language, and xsd:boolean.

Finally, OWL 2 QL does not support anonymous individuals.

Individual := NamedIndividual

3.2.2 Property Expressions

OWL 2 QL object and data property expressions are the same as in the structural specification [OWL 2 Specification].

3.2.3 Class Expressions

In OWL 2 QL, there are two types of class expressions. The subClassExpression production defines the class expressions that can occur as subclass expressions in SubClassOf axioms, and the superClassExpression production defines the classes that can occur as superclass expressions in SubClassOf axioms.

subClassExpression :=
    Class |
    subObjectSomeValuesFrom | DataSomeValuesFrom
subObjectSomeValuesFrom := 'ObjectSomeValuesFrom' '(' ObjectPropertyExpression owl:Thing ')'

superClassExpression :=
    Class |
    superObjectIntersectionOf | superObjectComplementOf |
    superObjectSomeValuesFrom | DataSomeValuesFrom
superObjectIntersectionOf := 'ObjectIntersectionOf' '(' superClassExpression superClassExpression { superClassExpression } ')'
superObjectComplementOf := 'ObjectComplementOf' '(' subClassExpression ')'
superObjectSomeValuesFrom := 'ObjectSomeValuesFrom' '(' ObjectPropertyExpression Class ')'

3.2.4 Data Ranges

A data range expression is restricted in OWL 2 QL to the predefined datatypes and the intersection of data ranges.

DataRange := Datatype | DataIntersectionOf

3.2.5 Axioms

The class axioms of OWL 2 QL are the same as in the structural specification [OWL 2 Specification], with the exception that DisjointUnion is disallowed; however, all axioms that refer to the ClassExpression production are redefined so as to use subClassExpression and/or superClassExpression as appropriate.

SubClassOf := 'SubClassOf' '(' axiomAnnotations subClassExpression superClassExpression ')'
EquivalentClasses := 'EquivalentClasses' '(' axiomAnnotations subClassExpression subClassExpression { subClassExpression } ')'
DisjointClasses := 'DisjointClasses' '(' axiomAnnotations subClassExpression subClassExpression { subClassExpression } ')'
ClassAxiom := SubClassOf | EquivalentClasses | DisjointClasses

OWL 2 QL disallows the use of property chains in property inclusion axioms; however, simple property inclusions are supported. Furthermore, OWL 2 QL disallows the use of functional, transitive, asymmetric, reflexive and irreflexive object properties, and it restricts the class expressions in object property domain and range axioms to superClassExpression.

ObjectPropertyDomain := 'ObjectPropertyDomain' '(' axiomAnnotations ObjectPropertyExpression superClassExpression ')'
ObjectPropertyRange := 'ObjectPropertyRange' '(' axiomAnnotations ObjectPropertyExpression superClassExpression ')'
SubObjectPropertyOf := 'SubObjectPropertyOf' '(' axiomAnnotations ObjectPropertyExpression ObjectPropertyExpression ')'
ObjectPropertyAxiom :=
    SubObjectPropertyOf | EquivalentObjectProperties |
    DisjointObjectProperties | InverseObjectProperties |
    ObjectPropertyDomain | ObjectPropertyRange |
    SymmetricObjectProperty

OWL 2 QL disallows functional data property axioms, and it restricts the class expressions in data property domain axioms to superClassExpression.

DataPropertyDomain := 'DataPropertyDomain' '(' axiomAnnotations DataPropertyExpression superClassExpression ')'
DataPropertyAxiom :=
    SubDataPropertyOf | EquivalentDataProperties | DisjointDataProperties |
    DataPropertyDomain | DataPropertyRange

OWL 2 QL disallows negative object property assertions and equality axioms. Furthermore, class assertions in OWL 2 QL can involve only atomic classes. Inequality axioms and property assertions are the same as in the structural specification [OWL 2 Specification].

ClassAssertion := 'ClassAssertion' '(' axiomAnnotations Class Individual ')'
Assertion := DifferentIndividuals | ClassAssertion | ObjectPropertyAssertion | DataPropertyAssertion

Finally, the axioms in OWL 2 QL are the same as those in the structural specification [OWL 2 Specification], with the exception that HasKey axioms are not allowed.

Axiom := Declaration | ClassAxiom | ObjectPropertyAxiom | DataPropertyAxiom | Assertion | AnnotationAxiom

4 OWL 2 RL

The OWL 2 RL profile is aimed at applications that require scalable reasoning without sacrificing too much expressive power. It is designed to accommodate both OWL 2 applications that can trade the full expressivity of the language for efficiency, and RDF(S) applications that need some added expressivity from OWL 2. This is achieved by defining a syntactic subset of OWL 2 which is amenable to implementation using rule-based technologies (see Section 4.2), and presenting a partial axiomatization of the OWL 2 RDF-Based Semantics [OWL 2 RDF-Based Semantics] in the form of first-order implications that can be used as the basis for such an implementation (see Section 4.3). The design of OWL 2 RL has been inspired by Description Logic Programs [DLP] and pD* [pD*].

For ontologies satisfying the syntactic constraints described in Section 4.2, a suitable rule-based implementation will have desirable computational properties; for example, it can return all and only the correct answers to certain kinds of query (see Section 4.3 and [Conformance]). Such an implementation can also be used with arbitrary RDF graphs. In this case, however, these properties no longer hold — in particular, it is no longer possible to guarantee that all correct answers can be returned, for example if the RDF graph uses the built-in vocabulary in unusual ways.

4.1 Feature Overview

Restricting the way in which constructs are used makes it possible to implement reasoning systems using rule-based reasoning engines, while still providing desirable computational guarantees. These restrictions are designed so as to avoid the need to infer the existence of individuals not explicitly present in the knowledge base, and to avoid the need for nondeterministic reasoning. This is achieved by restricting the use of constructs to certain syntactic positions. For example in SubClassOf axioms, the constructs in the subclass and superclass expressions must follow the usage patterns shown in Table 2.

Table 2. Syntactic Restrictions on Class Expressions in OWL 2 RL
Subclass Expressions Superclass Expressions
a class other than owl:Thing
an enumeration of individuals (ObjectOneOf)
intersection of class expressions (ObjectIntersectionOf)
union of class expressions (ObjectUnionOf)
existential quantification to a class expressions (ObjectSomeValuesFrom)
existential quantification to a data range (ObjectDataValuesFrom)
existential quantification to an individual (ObjectHasValue)
existential quantification to a literal (DataHasValue)
a class other than owl:Thing
intersection of classes (ObjectIntersectionOf)
universal quantification to a class expressions (ObjectAllValuesFrom)
existential quantification to an individual (ObjectHasValue)
at-most 1 cardinality restriction to a class expression (ObjectMaxCardinality 1)
universal quantification to a data range (DataAllValuesFrom)
existential quantification to a literal (DataHasValue)
at-most 1 cardinality restriction to a data range (DataMaxCardinality 1)

All axioms in OWL 2 RL are constrained in a way that is compliant with these restrictions. Thus, OWL 2 RL supports all axioms of OWL 2 apart from disjoint unions of classes (DisjointUnion), reflexive object property axioms (ReflexiveObjectProperty), and negative object and data property assertions (NegativeObjectPropertyAssertion and NegativeDataPropertyAssertion).

Implementations based on the partial axiomatization (presented in Section 4.3) can also be used with arbitrary RDF graphs, but in this case it is no longer possible to provide the above mentioned computational guarantees. Such implementations will, however, still produce only correct entailments (see [Conformance]).

4.2 Profile Specification

The productions for OWL 2 RL are defined in the following sections. OWL 2 RL is defined not only in terms of the set of supported constructs, but it also restricts the places in which these constructs can be used. Note that each OWL 2 RL ontology must satisfy the global restrictions on axioms defined in Section 11 of the structural specification [OWL 2 Specification].

4.2.1 Entities

Entities are defined in OWL 2 RL in the same way as in the structural specification [OWL 2 Specification]. OWL 2 RL supports the the predefined classes owl:Nothing and owl:Thing, but the usage of the latter class is restricted by the grammar of OWL 2 RL. Furthermore, OWL 2 RL does not support the predefined object and data properties owl:topObjectProperty, owl:bottomObjectProperty, owl:topDataProperty, and owl:bottomDataProperty. Finally, OWL 2 RL supports the following datatypes:

  • rdf:text
  • rdf:XMLLiteral
  • rdfs:Literal
  • xsd:decimal
  • xsd:integer
  • xsd:nonNegativeInteger
  • xsd:nonPositiveInteger
  • xsd:positiveInteger
  • xsd:negativeInteger
  • xsd:long
  • xsd:int
  • xsd:short
  • xsd:byte
  • xsd:unsignedLong
  • xsd:unsignedInt
  • xsd:unsignedShort
  • xsd:unsignedByte
  • xsd:float
  • xsd:double
  • xsd:string
  • xsd:normalizedString
  • xsd:token
  • xsd:language
  • xsd:Name
  • xsd:NCName
  • xsd:NMTOKEN
  • xsd:boolean
  • xsd:hexBinary
  • xsd:base64Binary
  • xsd:anyURI
  • xsd:dateTimeStamp

The set of supported datatypes has been designed to allow for an implementation in rule systems. The following datatypes MUST NOT be used in OWL 2 RL: owl:real, owl:realPlus, and owl:rational.

4.2.2 Property Expressions

Property expressions in OWL 2 RL are identical to the property expressions in the structural specification [OWL 2 Specification].

4.2.3 Class Expressions

There are three types of class expressions in OWL 2 RL. The subClassExpression production defines the class expressions that can occur as subclass expressions in SubClassOf axioms; the superClassExpression production defines the classes that can occur as superclass expressions in SubClassOf axioms; and the equivClassExpressions production defines the classes that can occur in EquivalentClasses axioms.

zeroOrOne  := '0' | '1'

subClassExpression :=
    Class other than owl:Thing |
    subObjectIntersectionOf | subObjectUnionOf | ObjectOneOf |
    subObjectSomeValuesFrom | ObjectHasValue |
    DataSomeValuesFrom | DataHasValue
subObjectIntersectionOf := 'ObjectIntersectionOf' '(' subClassExpression subClassExpression { subClassExpression } ')'
subObjectUnionOf := 'ObjectUnionOf' '(' subClassExpression subClassExpression { subClassExpression } ')'
subObjectSomeValuesFrom :=
    'ObjectSomeValuesFrom' '(' ObjectPropertyExpression subClassExpression ')' |
    'ObjectSomeValuesFrom' '(' ObjectPropertyExpression owl:Thing ')'

superClassExpression :=
    Class other than owl:Thing |
    superObjectIntersectionOf |
    superObjectAllValuesFrom | ObjectHasValue | superObjectMaxCardinality |
    DataAllValuesFrom | DataHasValue | superDataMaxCardinality
superObjectIntersectionOf := 'ObjectIntersectionOf' '(' superClassExpression superClassExpression { superClassExpression } ')'
superObjectAllValuesFrom := 'ObjectAllValuesFrom' '(' ObjectPropertyExpression superClassExpression ')'
superObjectMaxCardinality :=
    'ObjectMaxCardinality' '(' zeroOrOne ObjectPropertyExpression [ subClassExpression ] ')' |
    'ObjectMaxCardinality' '(' zeroOrOne ObjectPropertyExpression owl:Thing ')'
superDataMaxCardinality := 'DataMaxCardinality' '(' zeroOrOne DataPropertyExpression [ DataRange ] ')' |

equivClassExpression :=
    Class other than owl:Thing |
    equivObjectIntersectionOf |
    ObjectHasValue |
    DataHasValue
equivObjectIntersectionOf := 'ObjectIntersectionOf' '(' equivClassExpression equivClassExpression { equivClassExpression } ')'

4.2.4 Data Ranges

A data range expression is restricted in OWL 2 RL to the predefined datatypes admitted in OWL 2 RL and the intersection of data ranges.

DataRange := Datatype | DataIntersectionOf

4.2.5 Axioms

OWL 2 RL redefines all axioms of the structural specification [OWL 2 Specification] that refer to class expressions. In particular, it restricts various class axioms to use the appropriate form of class expressions (i.e., one of subClassExpression, superClassExpression, or equivClassExpression), and it disallows the DisjointUnion axiom.

ClassAxiom := SubClassOf | EquivalentClasses | DisjointClasses
SubClassOf := 'SubClassOf' '(' axiomAnnotations subClassExpression superClassExpression ')'
EquivalentClasses := 'EquivalentClasses' '(' axiomAnnotations equivClassExpression equivClassExpression { equivClassExpression } ')'
DisjointClasses := 'DisjointClasses' '(' axiomAnnotations subClassExpression subClassExpression { subClassExpression } ')'

OWL 2 RL axioms about property expressions are as in the structural specification [OWL 2 Specification], the only difference being that class expressions in property domain and range axioms are restricted to superClassExpression.

ObjectPropertyDomain := 'ObjectPropertyDomain' '(' axiomAnnotations ObjectPropertyExpression superClassExpression ')'
ObjectPropertyRange := 'ObjectPropertyRange' '(' axiomAnnotations ObjectPropertyExpression superClassExpression ')'
DataPropertyDomain := 'DataPropertyDomain' '(' axiomAnnotations DataPropertyExpression superClassExpression ')'

OWL 2 RL restricts class expressions in positive assertions to superClassExpression, and it disallows negative property assertions. Equality and inequality between individuals and positive assertions are the same as in the structural specification [OWL 2 Specification].

ClassAssertion := 'ClassAssertion' '(' axiomAnnotations Individual superClassExpression ')'
Assertion := SameIndividual | DifferentIndividuals | ClassAssertion | ObjectPropertyAssertion | DataPropertyAssertion

OWL 2 RL restricts class expressions in keys to subClassExpression.

HasKey := 'HasKey' '(' axiomAnnotations subClassExpression ObjectPropertyExpression | DataPropertyExpression { ObjectPropertyExpression | DataPropertyExpression } ')'

Axioms about properties are redefined in OWL 2 RL to disallow the reflexive properties.

ObjectPropertyAxiom :=
    SubObjectPropertyOf | EquivalentObjectProperties |
    DisjointObjectProperties | InverseObjectProperties |
    ObjectPropertyDomain | ObjectPropertyRange |
    FunctionalObjectProperty | InverseFunctionalObjectProperty |
    IrreflexiveObjectProperty |
    SymmetricObjectProperty | AsymmetricObjectProperty
    TransitiveObjectProperty

All other axioms in OWL 2 RL are defined as in the structural specification [OWL 2 Specification].

4.3 Reasoning in OWL 2 RL and RDF Graphs using Rules

This section presents a partial axiomatization of the OWL 2 RDF-Based Semantics [OWL 2 RDF-Based Semantics] in the form of first-order (material) implications; this axiomatization is called the OWL 2 RL/RDF rules. These rules provide a useful starting point for practical implementation using rule-based technologies.

The rules are given as universally quantified first-order implications over a ternary predicate T. This predicate represents a generalization of RDF triples in which bnodes and literals are allowed in all positions (similar to the partial generalization in pD* [pD*] and to generalized RDF triples in RIF [RIF]); thus, T(s, p, o) represents a generalized RDF triple with the subject s, predicate p, and the object o. Variables in the implications are preceded with a question mark. The propositional symbol false is a special symbol denoting contradiction: if it is derived, then the initial RDF graph was inconsistent. The set of rules listed in this section is not minimal, as certain rules are implied by other ones; this was done to make the definition of the semantic consequences of each piece of OWL 2 vocabulary self-contained.

Many conditions contain atoms that match to the list construct of RDF. In order to simplify the presentation of the rules, LIST[h, e1, ..., en] is used as an abbreviation for the conjunction of triples shown in Table 3, where z2, ..., zn are fresh variables that do not occur anywhere where the abbreviation is used.

Table 3. Expansion of LIST[h, e1, ..., en]
T(h, rdf:first, e1) T(h, rdf:rest, z2)
T(z2, rdf:first, e2) T(z2, rdf:rest, z3)
... ...
T(zn, rdf:first, en) T(zn, rdf:rest, rdf:nil)

The axiomatization is split into several tables for easier navigation. Each rule is given a short unique name.

Table 4 axiomatizes the semantics of equality. In particular, it defines the equality relation on resources owl:sameAs as being reflexive, symmetric, and transitive, and it axiomatizes the standard replacement properties of equality for it.

Table 4. The Semantics of Equality
If then
eq-ref T(?s, ?p, ?o)
T(?s, owl:sameAs, ?s)
T(?p, owl:sameAs, ?p)
T(?o, owl:sameAs, ?o)
eq-sym T(?x, owl:sameAs, ?y) T(?y, owl:sameAs, ?x)
eq-trans T(?x, owl:sameAs, ?y)
T(?y, owl:sameAs, ?z)
T(?x, owl:sameAs, ?z)
eq-rep-s T(?s, owl:sameAs, ?s')
T(?s, ?p, ?o)
T(?s', ?p, ?o)
eq-rep-p T(?p, owl:sameAs, ?p')
T(?s, ?p, ?o)
T(?s, ?p', ?o)
eq-rep-o T(?o, owl:sameAs, ?o')
T(?s, ?p, ?o)
T(?s, ?p, ?o')
eq-diff1 T(?x, owl:sameAs, ?y)
T(?x, owl:differentFrom, ?y)
false
eq-diff2 T(?yi, owl:sameAs, ?yj)
T(?x, rdf:type, owl:AllDifferent)
LIST[?x, ?y1, ..., ?yn]
false for each 1 ≤ i < j ≤ n

Table 5 specifies the semantic conditions on axioms about properties.

Table 5. The Semantics of Axioms about Properties
If then
prp-ap true T(ap, rdf:type, owl:AnnotationProperty) for each built-in annotation property of OWL 2 RL
prp-dom T(?p, rdfs:domain, ?c)
T(?x, ?p, ?y)
T(?x, rdf:type, ?c)
prp-rng T(?p, rdfs:range, ?c)
T(?x, ?p, ?y)
T(?y, rdf:type, ?c)
prp-fp T(?p, rdf:type, owl:FunctionalProperty)
T(?x, ?p, ?y1)
T(?x, ?p, ?y2)
T(?y1, owl:sameAs, ?y2)
prp-ifp T(?p, rdf:type, owl:InverseFunctionalProperty)
T(?x1, ?p, ?y)
T(?x2, ?p, ?y)
T(?x1, owl:sameAs, ?x2)
prp-irp T(?p, rdf:type, owl:IrreflexiveProperty)
T(?x, ?p, ?x)
false
prp-symp T(?p, rdf:type, owl:SymmetricProperty)
T(?x, ?p, ?y)
T(?y, ?p, ?x)
prp-asyp T(?p, rdf:type, owl:AsymmetricProperty)
T(?x, ?p, ?y)
T(?y, ?p, ?x)
false
prp-trp T(?p, rdf:type, owl:TransitiveProperty)
T(?x, ?p, ?y)
T(?y, ?p, ?z)
T(?x, ?p, ?z)
prp-spo1 T(?p1, rdfs:subPropertyOf, ?p2)
T(?x, ?p1, ?y)
T(?x, ?p2, ?y)
prp-spo2 T(?sc, owl:propertyChain, ?x)
LIST[?x, ?p1, ..., ?pn]
T(?sc, rdfs:subPropertyOf, ?p)
T(?u1, ?p1, ?u2)
T(?u2, ?p2, ?u3)
...
T(?un, ?pn, ?un+1)
T(?u1, ?p, ?un+1)
prp-eqp1 T(?p1, owl:equivalentProperty, ?p2)
T(?x, ?p1, ?y)
T(?x, ?p2, ?y)
prp-eqp2 T(?p1, owl:equivalentProperty, ?p2)
T(?x, ?p2, ?y)
T(?x, ?p1, ?y)
prp-pdw T(?p1, owl:propertyDisjointWith, ?p2)
T(?x, ?p1, ?y)
T(?x, ?p2, ?y)
false
prp-adp T(?z, rdf:type, owl:AllDisjointProperties)
LIST[?z, ?p1, ..., ?pn]
T(?x, ?pi, ?y)
T(?x, ?pj, ?y)
false for each 1 ≤ i < j ≤ n
prp-inv1 T(?p1, owl:inverseOf, ?p2)
T(?x, ?p1, ?y)
T(?y, ?p2, ?x)
prp-inv2 T(?p1, owl:inverseOf, ?p2)
T(?x, ?p2, ?y)
T(?y, ?p1, ?x)
prp-key T(?c, owl:hasKey, ?u)
LIST[?u, ?p1, ..., ?pn]
T(?x, rdf:type, ?c)
T(?x, ?p1, ?z1)
...
T(?x, ?pn, ?zn)
T(?y, rdf:type, ?c)
T(?y, ?p1, ?z1)
...
T(?y, ?pn, ?zn)
T(?x, owl:sameAs, ?y)

Table 6 specifies the semantic conditions on classes.

Table 6. The Semantics of Classes
If then
cls-thing true T(owl:Thing, rdf:type, owl:Class)
cls-nothing1 true T(owl:Nothing, rdf:type, owl:Class)
cls-nothing2 T(?x, rdf:type, owl:Nothing) false
cls-int1 T(?c, owl:intersectionOf, ?x)
LIST[?x, ?c1, ..., ?cn]
T(?y, rdf:type, ?c1)
T(?y, rdf:type, ?c2)
...
T(?y, rdf:type, ?cn)
T(?y, rdf:type, ?c)
cls-int2 T(?c, owl:intersectionOf, ?x)
LIST[?x, ?c1, ..., ?cn]
T(?y, rdf:type, ?c)
T(?y, rdf:type, ?c1)
T(?y, rdf:type, ?c2)
...
T(?y, rdf:type, ?cn)
cls-uni T(?c, owl:unionOf, ?x)
LIST[?x, ?c1, ..., ?cn]
T(?y, rdf:type, ?ci)
T(?y, rdf:type, ?c) for each 1 ≤ i ≤ n
cls-svf1 T(?x, owl:someValuesFrom, ?y)
T(?x, owl:onProperty, ?p)
T(?u, ?p, ?v)
T(?v, rdf:type, ?y)
T(?u, rdf:type, ?x)
cls-svf2 T(?x, owl:someValuesFrom, owl:Thing)
T(?x, owl:onProperty, ?p)
T(?u, ?p, ?v)
T(?u, rdf:type, ?x)
cls-avf T(?x, owl:allValuesFrom, ?y)
T(?x, owl:onProperty, ?p)
T(?u, rdf:type, ?x)
T(?u, ?p, ?v)
T(?v, rdf:type, ?y)
cls-hv1 T(?x, owl:hasValue, ?y)
T(?x, owl:onProperty, ?p)
T(?u, rdf:type, ?x)
T(?u, ?p, ?y)
cls-hv2 T(?x, owl:hasValue, ?y)
T(?x, owl:onProperty, ?p)
T(?u, ?p, ?y)
T(?u, rdf:type, ?x)
cls-maxc1 T(?x, owl:maxCardinality, "0"^^xsd:nonNegativeInteger)
T(?x, owl:onProperty, ?p)
T(?u, rdf:type, ?x)
T(?u, ?p, ?y)
false
cls-maxc2 T(?x, owl:maxCardinality, "1"^^xsd:nonNegativeInteger)
T(?x, owl:onProperty, ?p)
T(?u, rdf:type, ?x)
T(?u, ?p, ?y1)
T(?u, ?p, ?y2)
T(?y1, owl:sameAs, ?y2)
cls-maxqc1 T(?x, owl:maxQualifiedCardinality, "0"^^xsd:nonNegativeInteger)
T(?x, owl:onProperty, ?p)
T(?x, owl:onClass, ?c)
T(?u, rdf:type, ?x)
T(?u, ?p, ?y)
T(?y, rdf:type, ?c)
false
cls-maxqc2 T(?x, owl:maxQualifiedCardinality, "0"^^xsd:nonNegativeInteger)
T(?x, owl:onProperty, ?p)
T(?x, owl:onClass, owl:Thing)
T(?u, rdf:type, ?x)
T(?u, ?p, ?y)
false
cls-maxqc3 T(?x, owl:maxQualifiedCardinality, "1"^^xsd:nonNegativeInteger)
T(?x, owl:onProperty, ?p)
T(?x, owl:onClass, ?c)
T(?u, rdf:type, ?x)
T(?u, ?p, ?y1)
T(?y1, rdf:type, ?c)
T(?u, ?p, ?y2)
T(?y2, rdf:type, ?c)
T(?y1, owl:sameAs, ?y2)
cls-maxqc4 T(?x, owl:maxQualifiedCardinality, "1"^^xsd:nonNegativeInteger)
T(?x, owl:onProperty, ?p)
T(?x, owl:onClass, owl:Thing)
T(?u, rdf:type, ?x)
T(?u, ?p, ?y1)
T(?u, ?p, ?y2)
T(?y1, owl:sameAs, ?y2)
cls-oo T(?c, owl:oneOf, ?x)
LIST[?x, ?y1, ..., ?yn]
T(?yi, rdf:type, ?c) for each 1 ≤ i ≤ n

Table 7 specifies the semantic conditions on class axioms.

Table 7. The Semantics of Class Axioms
If then
cax-sco T(?c1, rdfs:subClassOf, ?c2)
T(?x, rdf:type, ?c1)
T(?x, rdf:type, ?c2)
cax-eqc1 T(?c1, owl:equivalentClass, ?c2)
T(?x, rdf:type, ?c1)
T(?x, rdf:type, ?c2)
cax-eqc2 T(?c1, owl:equivalentClass, ?c2)
T(?x, rdf:type, ?c2)
T(?x, rdf:type, ?c1)
cax-dw T(?c1, owl:disjointWith, ?c2)
T(?x, rdf:type, ?c1)
T(?x, rdf:type, ?c2)
false
cax-adc T(?y, rdf:type, owl:AllDisjointClasses)
LIST[?y, ?c1, ..., ?cn]
T(?x, rdf:type, ?ci)
T(?x, rdf:type, ?cj)
false for each 1 ≤ i < j ≤ n

Table 8 specifies the semantics of datatypes.

Table 8. The Semantics of Datatypes
If then
dt-type1 true T(dt, rdf:type, rdfs:Datatype) for each datatype dt supported in OWL 2 RL
dt-type2 true T(lt, rdf:type, dt) for each literal lt and each datatype dt supported in OWL 2 RL
such that the data value of lt is contained in the value space of dt
dt-eq true T(lt1, owl:sameAs, lt2) for all literals lt1 and lt2 with the same data value
dt-diff true T(lt1, owl:differentFrom, lt2) for all literals lt1 and lt2 with different data values
dt-not-type T(lt, rdf:type, dt) false for each literal lt and each datatype dt supported in OWL 2 RL
such that the data value of lt is not contained in the value space of dt

Table 9 specifies the semantic restrictions on the vocabulary used to define the schema.

Table 9. The Semantics of Schema Vocabulary
If then
scm-cls T(?c, rdf:type, owl:Class) T(?c, rdfs:subClassOf, ?c)
T(?c, owl:equivalentClass, ?c)
T(?c, rdfs:subClassOf, owl:Thing)
T(owl:Nothing, rdfs:subClassOf, ?c)
scm-sco T(?c1, rdfs:subClassOf, ?c2)
T(?c2, rdfs:subClassOf, ?c3)
T(?c1, rdfs:subClassOf, ?c3)
scm-eqc1 T(?c1, owl:equivalentClass, ?c2) T(?c1, rdfs:subClassOf, ?c2)
T(?c2, rdfs:subClassOf, ?c1)
scm-eqc2 T(?c1, rdfs:subClassOf, ?c2)
T(?c2, rdfs:subClassOf, ?c1)
T(?c1, owl:equivalentClass, ?c2)
scm-op T(?p, rdf:type, owl:ObjectProperty) T(?p, rdfs:subPropertyOf, ?p)
T(?p, owl:equivalentProperty, ?p)
scm-dp T(?p, rdf:type, owl:DatatypeProperty) T(?p, rdfs:subPropertyOf, ?p)
T(?p, owl:equivalentProperty, ?p)
scm-spo T(?p1, rdfs:subPropertyOf, ?p2)
T(?p2, rdfs:subPropertyOf, ?p3)
T(?p1, rdfs:subPropertyOf, ?p3)
scm-eqp1 T(?p1, owl:equivalentProperty, ?p2) T(?p1, rdfs:subPropertyOf, ?p2)
T(?p2, rdfs:subPropertyOf, ?p1)
scm-eqp2 T(?p1, rdfs:subPropertyOf, ?p2)
T(?p2, rdfs:subPropertyOf, ?p1)
T(?p1, owl:equivalentProperty, ?p2)
scm-dom1 T(?p, rdfs:domain, ?c1)
T(?c1, rdfs:subClassOf, ?c2)
T(?p, rdfs:domain, ?c2)
scm-dom2 T(?p2, rdfs:domain, ?c)
T(?p1, rdfs:subPropertyOf, ?p2)
T(?p1, rdfs:domain, ?c)
scm-rng1 T(?p, rdfs:range, ?c1)
T(?c1, rdfs:subClassOf, ?c2)
T(?p, rdfs:range, ?c2)
scm-rng2 T(?p2, rdfs:range, ?c)
T(?p1, rdfs:subPropertyOf, ?p2)
T(?p1, rdfs:range, ?c)
scm-hv T(?c1, owl:hasValue, ?i)
T(?c1, owl:onProperty, ?p1)
T(?c2, owl:hasValue, ?i)
T(?c2, owl:onProperty, ?p2)
T(?p1, rdfs:subPropertyOf, ?p2)
T(?c1, rdfs:subClassOf, ?c2)
scm-svf1 T(?c1, owl:someValuesFrom, ?y1)
T(?c1, owl:onProperty, ?p)
T(?c2, owl:someValuesFrom, ?y2)
T(?c2, owl:onProperty, ?p)
T(?y1, rdfs:subClassOf, ?y2)
T(?c1, rdfs:subClassOf, ?c2)
scm-svf2 T(?c1, owl:someValuesFrom, ?y)
T(?c1, owl:onProperty, ?p1)
T(?c2, owl:someValuesFrom, ?y)
T(?c2, owl:onProperty, ?p2)
T(?p1, rdfs:subPropertyOf, ?p2)
T(?c1, rdfs:subClassOf, ?c2)
scm-avf1 T(?c1, owl:allValuesFrom, ?y1)
T(?c1, owl:onProperty, ?p)
T(?c2, owl:allValuesFrom, ?y2)
T(?c2, owl:onProperty, ?p)
T(?y1, rdfs:subClassOf, ?y2)
T(?c1, rdfs:subClassOf, ?c2)
scm-avf2 T(?c1, owl:allValuesFrom, ?y)
T(?c1, owl:onProperty, ?p1)
T(?c2, owl:allValuesFrom, ?y)
T(?c2, owl:onProperty, ?p2)
T(?p1, rdfs:subPropertyOf, ?p2)
T(?c2, rdfs:subClassOf, ?c1)
scm-int T(?c, owl:intersectionOf, ?x)
LIST[?x, ?c1, ..., ?cn]
T(?c, rdfs:subClassOf, ?c1)
T(?c, rdfs:subClassOf, ?c2)
...
T(?c, rdfs:subClassOf, ?cn)
scm-uni T(?c, owl:unionOf, ?x)
LIST[?x, ?c1, ..., ?cn]
T(?c1, rdfs:subClassOf, ?c)
T(?c2, rdfs:subClassOf, ?c)
...
T(?cn, rdfs:subClassOf, ?c)

In order to avoid potential performance problems in practice, OWL 2 RL/RDF rules do not include the axiomatic triples of RDF and RDFS [RDF Semantics] and the relevant OWL vocabulary [OWL 2 RDF-Based Semantics]; moreover, OWL 2 RL/RDF rules include most, but not all of the entailment rules of RDFS [RDF Semantics]. An OWL 2 RL/RDF implementation MAY include these triples and entailment rules as necessary without invalidating the conformance requirements for OWL 2 RL [Conformance].

Theorem PR1. Let R be the OWL 2 RL/RDF rules as defined above. Furthermore, let O1 and O2 be OWL 2 RL ontologies satisfying the following properties:

  • neither O1 nor O2 contains a IRI that is used for more than one type of entity (i.e., no IRIs is used both as, say, a class and an individual);
  • O1 does not contain SubAnnotationPropertyOf, AnnotationPropertyDomain, and AnnotationPropertyRange axioms; and
  • each axiom in O2 is an assertion of the form as specified below, for a, a1, ..., an named individuals:
    • ClassAssertion( C a ) where C is a class,
    • ObjectPropertyAssertion( OP a1 a2 ) where OP is an object property,
    • DataPropertyAssertion( DP a v ) where DP is a data property, or
    • SameIndividual( a1 ... an ).

Furthermore, let RDF(O1) and RDF(O2) be translations of O1 and O2, respectively, into RDF graphs as specified in the OWL 2 Mapping to RDF Graphs [OWL 2 RDF Mapping]; and let FO(RDF(O1)) and FO(RDF(O2)) be the translation of these graphs into first-order theories in which triples are represented using the T predicate — that is, T(s, p, o) represents an RDF triple with the subject s, predicate p, and the object o. Then, O1 entails O2 under the OWL 2 Direct Semantics [OWL 2 Direct Semantics] if and only if FO(RDF(O1))R entails FO(RDF(O2)) under the standard first-order semantics.

Proof Sketch. Without loss of generality, it can be assumed that all axioms in O1 are fully normalized — that is, that all class expressions in the axioms are of depth at most one. Let DLP(O1) be the set of rules obtained by translating O1 into a set of rules as in Description Logic Programs [DLP].

Consider now each assertion AO2 that is entailed by DLP(O1) (or, equivalently, by O1). Let dt be a derivation tree for A from DLP(O1). By examining the set of OWL 2 RL constructs, it is possible to see that each such tree can be transformed to a derivation tree dt' for FO(RDF(A)) from FO(RDF(O1))R. Each assertion B occurring in dt is of the form as specified in the theorem. The tree dt' can, roughly speaking, be obtained from dt by replacing each assertion B with FO(RDF(B)) and by replacing each rule from DLP(O1) with a corresponding rule from Tables 3–8. Consequently, FO(RDF(O1))R entails FO(RDF(A)).

Since no IRI in O1 is used as both an individual and a class or a property, FO(RDF(O1))R does not entail a triple of the form T(a:i1, owl:sameAs, a:i2) where either a:i1 or a:i2 is used in O1 as a class or a property. This allows one to transform a derivation tree for FO(RDF(A)) from FO(RDF(O1))R to a derivation tree for A from DLP(O1) in a way that is analogous to the previous case. QED

5 Computational Properties

This section describes the computational complexity of the most relevant reasoning problems of the languages defined in this document. For an introduction to computational complexity, please refer to a textbook on complexity such as [Papadimitriou]. The reasoning problems considered here are ontology consistency, class expression satisfiability, class expression subsumption, instance checking, and (Boolean) conjunctive query answering [OWL 2 Direct Semantics]. When evaluating complexity, the following parameters will be considered:

  • Data Complexity: the complexity measured with respect to the total size of the assertions in the ontology.
  • Taxonomic Complexity: the complexity measured with respect to the total size of the axioms in the ontology.
  • Query Complexity: the complexity measured with respect to the total size of the query.
  • Combined Complexity: the complexity measured with respect to both the size of the axioms, the size of the assertions, and, in the case of conjunctive query answering, the size of the query as well.

Table 10 summarizes the known complexity results for OWL 2 under both RDF and the direct semantics, OWL 2 EL, OWL 2 QL, OWL 2 RL, and OWL 1 DL. The meaning of the entries is as follows:

  • Decidability open means that it is not known whether this reasoning problem is decidable at all.
  • Decidable, but complexity open means that decidability of this reasoning problem is known, but not its exact computational complexity. If available, known lower bounds are given in parenthesis; for example, (NP-Hard) means that this problem is at least as hard as any other problem in NP.
  • X-complete for X one of the complexity classes explained below indicates that tight complexity bounds are known — that is, the problem is known to be both in the complexity class X (i.e., an algorithm is known that only uses time/space in X) and hard for X (i.e., it is at least as hard as any other problem in X). The following is a brief sketch of the classes used in this table, from the most complex one down to the simplest ones.
    • 2NEXPTIME is the class of problems solvable by a nondeterministic algorithm in time that is at most double exponential in the size of the input (i.e., roughly 22n, for n the size of the input).
    • NEXPTIME is the class of problems solvable by a nondeterministic algorithm in time that is at most exponential in the size of the input (i.e., roughly 2n, for n the size of the input).
    • PSPACE is the class of problems solvable by a nondeterministic algorithm using space that is at most polynomial in the size of the input (i.e., roughly nc, for n the size of the input and c a constant).
    • NP is the class of problems solvable by a nondeterministic algorithm using time that is at most polynomial in the size of the input (i.e., roughly nc, for n the size of the input and c a constant).
    • PTIME is the class of problems solvable by a deterministic algorithm using time that is at most polynomial in the size of the input (i.e., roughly nc, for n the size of the input and c a constant). PTIME is often referred to as tractable, whereas the problems in the classes above are often referred to as intractable.
    • LOGSPACE is the class of problems solvable by a deterministic algorithm using space that is at most logarithmic in the size of the input (i.e., roughly log(n), for n the size of the input and c a constant).

The results below refer to the worst-case complexity of these reasoning problems and, as such, do not say that implemented algorithms necessarily run in this class on all input problems, or what space/time they use on some/typical/certain kind of problems. For X-complete problems, these results only say that a reasoning algorithm cannot use less time/space than indicated by this class on all input problems.

Table 10. Complexity of the Profiles
Language Reasoning Problems Taxonomic Complexity Data Complexity Query Complexity Combined Complexity
OWL 2
RDF-Based Semantics
Ontology Consistency, Class Expression Satisfiability,
Class Expression Subsumption, Instance Checking,
Conjunctive Query Answering
Undecidable Undecidable Undecidable Undecidable
OWL 2
Direct Semantics
Ontology Consistency, Class Expression Satisfiability,
Class Expression Subsumption, Instance Checking
2NEXPTIME-complete (NEXPTIME if property hierarchies are bounded) Decidable, but complexity open
(NP-Hard)
Not Applicable 2NEXPTIME-complete (NEXPTIME if property hierarchies are bounded)
Conjunctive Query Answering Decidability open Decidability open Decidability open Decidability open
OWL 2 EL Ontology Consistency, Class Expression Satisfiability,
Class Expression Subsumption, Instance Checking
PTIME-complete PTIME-complete Not Applicable PTIME-complete
Conjunctive Query Answering PTIME-complete PTIME-complete NP-complete PSPACE-complete
OWL 2 QL Ontology Consistency, Class Expression Satisfiability,
Class Expression Subsumption, Instance Checking,
In PTIME In LOGSPACE Not Applicable In PTIME
Conjunctive Query Answering In PTIME In LOGSPACE NP-complete NP-complete
OWL 2 RL Ontology Consistency, Class Expression Satisfiability,
Class Expression Subsumption, Instance Checking
PTIME-complete PTIME-complete Not Applicable PTIME-complete
Conjunctive Query Answering PTIME-complete PTIME-complete NP-complete NP-complete
OWL 1 DL Ontology Consistency, Class Expression Satisfiability,
Class Expression Subsumption, Instance Checking
NEXPTIME-complete Decidable, but complexity open
(NP-Hard)
Not Applicable NEXPTIME-complete
Conjunctive Query Answering Decidability open Decidability open Decidability open Decidability open

6 Appendix: Complete Grammars for Profiles

This appendix contains the grammars for all three profiles of OWL 2.

6.1 OWL 2 EL

The grammar of OWL 2 EL consists of the general definitions from Section 13.1 of the OWL 2 Specification [OWL 2 Specification], as well as the following productions.

Class := IRI

Datatype := IRI

ObjectProperty := IRI

DataProperty := IRI

AnnotationProperty := IRI

Individual := NamedIndividual

NamedIndividual := IRI

Literal := typedLiteral | abbreviatedXSDStringLiteral | abbreviatedRDFTextLiteral
typedLiteral := lexicalValue '^^' Datatype
lexicalValue := quotedString
abbreviatedXSDStringLiteral := quotedString
abbreviatedRDFTextLiteral := quotedString '@' languageTag



ObjectPropertyExpression := ObjectProperty

DataPropertyExpression := DataProperty



DataRange := Datatype | DataIntersectionOf | DataOneOf

DataIntersectionOf := 'DataIntersectionOf' '(' DataRange DataRange { DataRange } ')'

DataOneOf := 'DataOneOf' '(' Literal ')'



ClassExpression :=
    Class | ObjectIntersectionOf | ObjectOneOf |
    ObjectSomeValuesFrom | ObjectHasValue | ObjectHasSelf |
    DataSomeValuesFrom | DataHasValue

ObjectIntersectionOf := 'ObjectIntersectionOf' '(' ClassExpression ClassExpression { ClassExpression } ')'

ObjectOneOf := 'ObjectOneOf' '(' Individual ')'

ObjectSomeValuesFrom := 'ObjectSomeValuesFrom' '(' ObjectPropertyExpression ClassExpression ')'

ObjectHasValue := 'ObjectHasValue' '(' ObjectPropertyExpression Individual ')'

ObjectHasSelf := 'ObjectHasSelf' '(' ObjectPropertyExpression ')'

DataSomeValuesFrom := 'DataSomeValuesFrom' '(' DataPropertyExpression { DataPropertyExpression } DataRange ')'

DataHasValue := 'DataHasValue' '(' DataPropertyExpression Literal ')'



Axiom := Declaration | ClassAxiom | ObjectPropertyAxiom | DataPropertyAxiom | HasKey | Assertion | AnnotationAxiom



ClassAxiom := SubClassOf | EquivalentClasses | DisjointClasses
SubClassOf := 'SubClassOf' '(' axiomAnnotations subClassExpression superClassExpression ')'
subClassExpression := ClassExpression
superClassExpression := ClassExpression

EquivalentClasses := 'EquivalentClasses' '(' axiomAnnotations ClassExpression ClassExpression { ClassExpression } ')'

DisjointClasses := 'DisjointClasses' '(' axiomAnnotations ClassExpression ClassExpression { ClassExpression } ')'



ObjectPropertyAxiom :=
    EquivalentObjectProperties | SubObjectPropertyOf |
    ObjectPropertyDomain | ObjectPropertyRange |
    ReflexiveObjectProperty | TransitiveObjectProperty

SubObjectPropertyOf := 'SubObjectPropertyOf' '(' axiomAnnotations subObjectPropertyExpression superObjectPropertyExpression ')'
subObjectPropertyExpression := ObjectPropertyExpression | propertyExpressionChain
propertyExpressionChain := 'ObjectPropertyChain' '(' ObjectPropertyExpression ObjectPropertyExpression { ObjectPropertyExpression } ')'
superObjectPropertyExpression := ObjectPropertyExpression

EquivalentObjectProperties := 'EquivalentObjectProperties' '(' axiomAnnotations ObjectPropertyExpression ObjectPropertyExpression { ObjectPropertyExpression } ')'

ObjectPropertyDomain := 'ObjectPropertyDomain' '(' axiomAnnotations ObjectPropertyExpression ClassExpression ')'

ObjectPropertyRange := 'ObjectPropertyRange' '(' axiomAnnotations ObjectPropertyExpression ClassExpression ')'

ReflexiveObjectProperty := 'ReflexiveObjectProperty' '(' axiomAnnotations ObjectPropertyExpression ')'

TransitiveObjectProperty := 'TransitiveObjectProperty' '(' axiomAnnotations ObjectPropertyExpression ')'



DataPropertyAxiom :=
    SubDataPropertyOf | EquivalentDataProperties |
    DataPropertyDomain | DataPropertyRange | FunctionalDataProperty

SubDataPropertyOf := 'SubDataPropertyOf' '(' axiomAnnotations subDataPropertyExpression superDataPropertyExpression ')'
subDataPropertyExpression := DataPropertyExpression
superDataPropertyExpression := DataPropertyExpression

EquivalentDataProperties := 'EquivalentDataProperties' '(' axiomAnnotations DataPropertyExpression DataPropertyExpression { DataPropertyExpression } ')'

DataPropertyDomain := 'DataPropertyDomain' '(' axiomAnnotations DataPropertyExpression ClassExpression ')'

DataPropertyRange := 'DataPropertyRange' '(' axiomAnnotations DataPropertyExpression DataRange ')'

FunctionalDataProperty := 'FunctionalDataProperty' '(' axiomAnnotations DataPropertyExpression ')'



HasKey := 'HasKey' '(' axiomAnnotations ClassExpression ObjectPropertyExpression | DataPropertyExpression { ObjectPropertyExpression | DataPropertyExpression } ')'



Assertion :=
    SameIndividual | DifferentIndividuals | ClassAssertion |
    ObjectPropertyAssertion | NegativeObjectPropertyAssertion |
    DataPropertyAssertion | NegativeDataPropertyAssertion

sourceIndividual := Individual
targetIndividual := Individual
targetValue := Literal

SameIndividual := 'SameIndividual' '(' axiomAnnotations Individual Individual { Individual } ')'

DifferentIndividuals := 'DifferentIndividuals' '(' axiomAnnotations Individual Individual { Individual } ')'

ClassAssertion := 'ClassAssertion' '(' axiomAnnotations ClassExpression Individual ')'

ObjectPropertyAssertion := 'ObjectPropertyAssertion' '(' axiomAnnotations ObjectPropertyExpression sourceIndividual targetIndividual ')'

NegativeObjectPropertyAssertion := 'NegativeObjectPropertyAssertion' '(' axiomAnnotations objectPropertyExpression sourceIndividual targetIndividual ')'

DataPropertyAssertion := 'DataPropertyAssertion' '(' axiomAnnotations DataPropertyExpression sourceIndividual targetValue ')'

NegativeDataPropertyAssertion := 'NegativeDataPropertyAssertion' '(' axiomAnnotations DataPropertyExpression sourceIndividual targetValue ')'

6.2 OWL 2 QL

The grammar of OWL 2 QL consists of the general definitions from Section 13.1 of the OWL 2 Specification [OWL 2 Specification], as well as the following productions.

Class := IRI

Datatype := IRI

ObjectProperty := IRI

DataProperty := IRI

AnnotationProperty := IRI

Individual := NamedIndividual

NamedIndividual := IRI

Literal := typedLiteral | abbreviatedXSDStringLiteral | abbreviatedRDFTextLiteral
typedLiteral := lexicalValue '^^' Datatype
lexicalValue := quotedString
abbreviatedXSDStringLiteral := quotedString
abbreviatedRDFTextLiteral := quotedString '@' languageTag



ObjectPropertyExpression := ObjectProperty | InverseObjectProperty

InverseObjectProperty := 'InverseOf' '(' ObjectProperty ')'

DataPropertyExpression := DataProperty



DataRange := Datatype | DataIntersectionOf

DataIntersectionOf := 'IntersectionOf' '(' DataRange DataRange { DataRange } ')'



subClassExpression :=
    Class |
    subObjectSomeValuesFrom | DataSomeValuesFrom

subObjectSomeValuesFrom := 'SomeValuesFrom' '(' ObjectPropertyExpression owl:Thing ')'

superClassExpression :=
    Class |
    superObjectIntersectionOf | superObjectComplementOf |
    superObjectSomeValuesFrom | DataSomeValuesFrom

superObjectIntersectionOf := 'IntersectionOf' '(' superClassExpression superClassExpression { superClassExpression } ')'

superObjectComplementOf := 'ComplementOf' '(' subClassExpression ')'

superObjectSomeValuesFrom := 'SomeValuesFrom' '(' ObjectPropertyExpression Class ')'

DataSomeValuesFrom := 'SomeValuesFrom' '(' DataPropertyExpression DataRange ')'



Axiom := Declaration | ClassAxiom | ObjectPropertyAxiom | DataPropertyAxiom | Assertion | AnnotationAxiom



ClassAxiom := SubClassOf | EquivalentClasses | DisjointClasses

SubClassOf := 'SubClassOf' '(' axiomAnnotations subClassExpression superClassExpression ')'

EquivalentClasses := 'EquivalentClasses' '(' axiomAnnotations subClassExpression subClassExpression { subClassExpression } ')'

DisjointClasses := 'DisjointClasses' '(' axiomAnnotations subClassExpression subClassExpression { subClassExpression } ')'



ObjectPropertyAxiom :=
    SubObjectPropertyOf | EquivalentObjectProperties |
    DisjointObjectProperties | InverseObjectProperties |
    ObjectPropertyDomain | ObjectPropertyRange |
    SymmetricObjectProperty

SubObjectPropertyOf := 'SubPropertyOf' '(' axiomAnnotations ObjectPropertyExpression ObjectPropertyExpression ')'

EquivalentObjectProperties := 'EquivalentProperties' '(' axiomAnnotations ObjectPropertyExpression ObjectPropertyExpression { ObjectPropertyExpression } ')'

DisjointObjectProperties := 'DisjointProperties' '(' axiomAnnotations ObjectPropertyExpression ObjectPropertyExpression { ObjectPropertyExpression } ')'

InverseObjectProperties := 'InverseProperties' '(' axiomAnnotations ObjectPropertyExpression ObjectPropertyExpression ')'

ObjectPropertyDomain := 'PropertyDomain' '(' axiomAnnotations ObjectPropertyExpression superClassExpression ')'

ObjectPropertyRange := 'PropertyRange' '(' axiomAnnotations ObjectPropertyExpression superClassExpression ')'

SymmetricObjectProperty := 'SymmetricProperty' '(' axiomAnnotations ObjectPropertyExpression ')'



DataPropertyAxiom :=
    SubDataPropertyOf | EquivalentDataProperties | DisjointDataProperties |
    DataPropertyDomain | DataPropertyRange

SubDataPropertyOf := 'SubPropertyOf' '(' axiomAnnotations subDataPropertyExpression superDataPropertyExpression ')'
subDataPropertyExpression := DataPropertyExpression
superDataPropertyExpression := DataPropertyExpression

EquivalentDataProperties := 'EquivalentProperties' '(' axiomAnnotations DataPropertyExpression DataPropertyExpression { DataPropertyExpression } ')'

DisjointDataProperties := 'DisjointProperties' '(' axiomAnnotations DataPropertyExpression DataPropertyExpression { DataPropertyExpression } ')'

DataPropertyDomain := 'PropertyDomain' '(' axiomAnnotations DataPropertyExpression superClassExpression ')'

DataPropertyRange := 'PropertyRange' '(' axiomAnnotations DataPropertyExpression DataRange ')'



Assertion := DifferentIndividuals | ClassAssertion | ObjectPropertyAssertion | DataPropertyAssertion

sourceIndividual := Individual
targetIndividual := Individual
targetValue := Literal

DifferentIndividuals := 'DifferentIndividuals' '(' axiomAnnotations Individual Individual { Individual } ')'

ClassAssertion := 'ClassAssertion' '(' axiomAnnotations Class Individual ')'

ObjectPropertyAssertion := 'PropertyAssertion' '(' axiomAnnotations ObjectPropertyExpression sourceIndividual targetIndividual ')'

DataPropertyAssertion := 'PropertyAssertion' '(' axiomAnnotations DataPropertyExpression sourceIndividual targetValue ')'

6.3 OWL 2 RL

The grammar of OWL 2 RL consists of the general definitions from Section 13.1 of the OWL 2 Specification [OWL 2 Specification], as well as the following productions.

Class := IRI

Datatype := IRI

ObjectProperty := IRI

DataProperty := IRI

AnnotationProperty := IRI

Individual := NamedIndividual | AnonymousIndividual

NamedIndividual := IRI

AnonymousIndividual := nodeID

Literal := typedLiteral | abbreviatedXSDStringLiteral | abbreviatedRDFTextLiteral
typedLiteral := lexicalValue '^^' Datatype
lexicalValue := quotedString
abbreviatedXSDStringLiteral := quotedString
abbreviatedRDFTextLiteral := quotedString '@' languageTag



ObjectPropertyExpression := ObjectProperty | InverseObjectProperty

InverseObjectProperty := 'InverseOf' '(' ObjectProperty ')'

DataPropertyExpression := DataProperty



DataRange := Datatype | DataIntersectionOf

DataIntersectionOf := 'IntersectionOf' '(' DataRange DataRange { DataRange } ')'



zeroOrOne  := '0' | '1'

subClassExpression :=
    Class other than owl:Thing |
    subObjectIntersectionOf | subObjectUnionOf | ObjectOneOf |
    subObjectSomeValuesFrom | ObjectHasValue |
    DataSomeValuesFrom | DataHasValue

subObjectIntersectionOf := 'IntersectionOf' '(' subClassExpression subClassExpression { subClassExpression } ')'

subObjectUnionOf := 'UnionOf' '(' subClassExpression subClassExpression { subClassExpression } ')'

subObjectSomeValuesFrom :=
    'SomeValuesFrom' '(' ObjectPropertyExpression subClassExpression ')' |
    'SomeValuesFrom' '(' ObjectPropertyExpression owl:Thing ')'

superClassExpression :=
    Class other than owl:Thing |
    superObjectIntersectionOf |
    superObjectAllValuesFrom | ObjectHasValue | superObjectMaxCardinality |
    DataAllValuesFrom | DataHasValue | superDataMaxCardinality

superObjectIntersectionOf := 'IntersectionOf' '(' superClassExpression superClassExpression { superClassExpression } ')'

superObjectAllValuesFrom := 'AllValuesFrom' '(' ObjectPropertyExpression superClassExpression ')'

superObjectMaxCardinality :=
    'MaxCardinality' '(' zeroOrOne ObjectPropertyExpression [ subClassExpression ] ')' |
    'MaxCardinality' '(' zeroOrOne ObjectPropertyExpression owl:Thing ')'

superDataMaxCardinality := 'MaxCardinality' '(' zeroOrOne DataPropertyExpression [ DataRange ] ')' |

equivClassExpression :=
    Class other than owl:Thing |
    equivObjectIntersectionOf |
    ObjectHasValue |
    DataHasValue

equivObjectIntersectionOf := 'IntersectionOf' '(' equivClassExpression equivClassExpression { equivClassExpression } ')'

ObjectOneOf := 'OneOf' '(' Individual { Individual }')'

ObjectHasValue := 'HasValue' '(' ObjectPropertyExpression Individual ')'

DataSomeValuesFrom := 'SomeValuesFrom' '(' DataPropertyExpression { DataPropertyExpression } DataRange ')'

DataAllValuesFrom := 'AllValuesFrom' '(' DataPropertyExpression { DataPropertyExpression } DataRange ')'

DataHasValue := 'HasValue' '(' DataPropertyExpression Literal ')'



Axiom := Declaration | ClassAxiom | ObjectPropertyAxiom | DataPropertyAxiom | HasKey | Assertion | AnnotationAxiom



ClassAxiom := SubClassOf | EquivalentClasses | DisjointClasses

SubClassOf := 'SubClassOf' '(' axiomAnnotations subClassExpression superClassExpression ')'

EquivalentClasses := 'EquivalentClasses' '(' axiomAnnotations equivClassExpression equivClassExpression { equivClassExpression } ')'

DisjointClasses := 'DisjointClasses' '(' axiomAnnotations subClassExpression subClassExpression { subClassExpression } ')'



ObjectPropertyAxiom :=
    SubObjectPropertyOf | EquivalentObjectProperties |
    DisjointObjectProperties | InverseObjectProperties |
    ObjectPropertyDomain | ObjectPropertyRange |
    FunctionalObjectProperty | InverseFunctionalObjectProperty |
    IrreflexiveObjectProperty |
    SymmetricObjectProperty | AsymmetricObjectProperty
    TransitiveObjectProperty

SubObjectPropertyOf := 'SubPropertyOf' '(' axiomAnnotations subObjectPropertyExpression superObjectPropertyExpression ')'
subObjectPropertyExpression := ObjectPropertyExpression | propertyExpressionChain
propertyExpressionChain := 'PropertyChain' '(' ObjectPropertyExpression ObjectPropertyExpression { ObjectPropertyExpression } ')'
superObjectPropertyExpression := ObjectPropertyExpression

EquivalentObjectProperties := 'EquivalentProperties' '(' axiomAnnotations ObjectPropertyExpression ObjectPropertyExpression { ObjectPropertyExpression } ')'

DisjointObjectProperties := 'DisjointProperties' '(' axiomAnnotations ObjectPropertyExpression ObjectPropertyExpression { ObjectPropertyExpression } ')'

InverseObjectProperties := 'InverseProperties' '(' axiomAnnotations ObjectPropertyExpression ObjectPropertyExpression ')'

ObjectPropertyDomain := 'PropertyDomain' '(' axiomAnnotations ObjectPropertyExpression superClassExpression ')'

ObjectPropertyRange := 'PropertyRange' '(' axiomAnnotations ObjectPropertyExpression superClassExpression ')'

FunctionalObjectProperty := 'FunctionalProperty' '(' axiomAnnotations ObjectPropertyExpression ')'

InverseFunctionalObjectProperty := 'InverseFunctionalProperty' '(' axiomAnnotations ObjectPropertyExpression ')'

ReflexiveObjectProperty := 'ReflexiveProperty' '(' axiomAnnotations ObjectPropertyExpression ')'

IrreflexiveObjectProperty := 'IrreflexiveProperty' '(' axiomAnnotations ObjectPropertyExpression ')'

SymmetricObjectProperty := 'SymmetricProperty' '(' axiomAnnotations ObjectPropertyExpression ')'

AsymmetricObjectProperty := 'AsymmetricProperty' '(' axiomAnnotations ObjectPropertyExpression ')'

TransitiveObjectProperty := 'TransitiveProperty' '(' axiomAnnotations ObjectPropertyExpression ')'



DataPropertyAxiom :=
    SubDataPropertyOf | EquivalentDataProperties | DisjointDataProperties |
    DataPropertyDomain | DataPropertyRange | FunctionalDataProperty

SubDataPropertyOf := 'SubPropertyOf' '(' axiomAnnotations subDataPropertyExpression superDataPropertyExpression ')'
subDataPropertyExpression := DataPropertyExpression
superDataPropertyExpression := DataPropertyExpression

EquivalentDataProperties := 'EquivalentProperties' '(' axiomAnnotations DataPropertyExpression DataPropertyExpression { DataPropertyExpression } ')'

DisjointDataProperties := 'DisjointProperties' '(' axiomAnnotations DataPropertyExpression DataPropertyExpression { DataPropertyExpression } ')'

DataPropertyDomain := 'PropertyDomain' '(' axiomAnnotations DataPropertyExpression superClassExpression ')'

DataPropertyRange := 'PropertyRange' '(' axiomAnnotations DataPropertyExpression DataRange ')'

FunctionalDataProperty := 'FunctionalProperty' '(' axiomAnnotations DataPropertyExpression ')'



HasKey := 'HasKey' '(' axiomAnnotations subClassExpression ObjectPropertyExpression | DataPropertyExpression { ObjectPropertyExpression | DataPropertyExpression } ')'



Assertion := SameIndividual | DifferentIndividuals | ClassAssertion | ObjectPropertyAssertion | DataPropertyAssertion

sourceIndividual := Individual
targetIndividual := Individual
targetValue := Literal

SameIndividual := 'SameIndividual' '(' axiomAnnotations Individual Individual { Individual } ')'

DifferentIndividuals := 'DifferentIndividuals' '(' axiomAnnotations Individual Individual { Individual } ')'

ClassAssertion := 'ClassAssertion' '(' axiomAnnotations Individual superClassExpression ')'

ObjectPropertyAssertion := 'PropertyAssertion' '(' axiomAnnotations ObjectPropertyExpression sourceIndividual targetIndividual ')'

DataPropertyAssertion := 'PropertyAssertion' '(' axiomAnnotations DataPropertyExpression sourceIndividual targetValue ')'

7 Acknowledgments

The starting point for the development of OWL 2 was the OWL1.1 member submission, itself a result of user and developer feedback, and in particular of information gathered during the OWL Experiences and Directions (OWLED) Workshop series. The working group also considered postponed issues from the WebOnt Working Group.

This document has been produced by the OWL Working Group (see below), and its contents reflect extensive discussions within the Working Group as a whole. The editors extend special thanks to Jim Hendler (RPI) and Jeff Pan (University of Aberdeen) for their thorough reviews.

The regular attendees at meetings of the OWL Working Group at the time of publication of this document were: Jie Bao (RPI), Diego Calvanese (Free University of Bozen-Bolzano), Bernardo Cuenca Grau (Oxford University Computing Laboratory), Martin Dzbor (Open University), Achille Fokoue (IBM Corporation), Christine Golbreich (Université de Versailles St-Quentin and LIRMM), Sandro Hawke (W3C/MIT), Ivan Herman (W3C/ERCIM), Rinke Hoekstra (University of Amsterdam), Ian Horrocks (Oxford University Computing Laboratory), Elisa Kendall (Sandpiper Software), Markus Krötzsch (FZI), Carsten Lutz (Universität Bremen), Deborah L. McGuinness (RPI), Boris Motik (Oxford University Computing Laboratory), Jeff Pan (University of Aberdeen), Bijan Parsia (University of Manchester), Peter F. Patel-Schneider (Bell Labs Research, Alcatel-Lucent), Sebastian Rudolph (FZI), Alan Ruttenberg (Science Commons), Uli Sattler (University of Manchester), Michael Schneider (FZI), Mike Smith (Clark & Parsia), Evan Wallace (NIST), Zhe Wu (Oracle Corporation), and Antoine Zimmermann (DERI Galway). We would also like to thank past members of the working group: Jeremy Carroll, Jim Hendler, and Vipul Kashyap.

8 References

[OWL 2 Specification]
OWL 2 Web Ontology Language: Structural Specification and Functional-Style Syntax. Boris Motik, Peter F. Patel-Schneider, and Bijan Parsia, eds., 2008
[OWL 2 Direct Semantics]
OWL 2 Web Ontology Language: Direct Semantics. Boris Motik, Peter F. Patel-Schneider, and Bernardo Cuenca Grau , eds., 2008
[OWL 2 RDF Mapping]
OWL 2 Web Ontology Language: Mapping to RDF Graphs.Peter F. Patel-Schneider and Boris Motik, eds., 2008
[OWL 2 RDF-Based Semantics]
OWL 2 RDF-Based Semantics. Michael Schneider, ed., 2008
[OWL 1 Reference]
OWL Web Ontology Language Reference. Mike Dean and Guus Screiber, eds., 2004
[Conformance]
Conformance. Michael Smith, Ian Horrocks, and Markus Krötzsch, eds., 2008
[RDF Semantics]
RDF Semantics. Patrick Hayes, ed., W3C Recommendation 2004
[DL Handbook]
The Description Logic Handbook. Franz Baader, Diego Calvanese, Deborah L. McGuinness, Daniele Nardi, Peter F. Patel-Schneider, eds., 2007
[EL++]
Pushing the EL Envelope. Franz Baader, Sebastian Brandt, and Carsten Lutz. In Proc. of the 19th Joint Int. Conf. on Artificial Intelligence (IJCAI 2005), 2005
[EL++ Update]
Pushing the EL Envelope Further. Franz Baader, Sebastian Brandt, and Carsten Lutz. In Proc. of the Washington DC workshop on OWL: Experiences and Directions (OWLED08DC), 2008
[DL-Lite]
Tractable Reasoning and Efficient Query Answering in Description Logics: The DL-Lite Family. Diego Calvanese, Giuseppe de Giacomo, Domenico Lembo, Maurizio Lenzerini, Riccardo Rosati. J. of Automated Reasoning 39(3):385–429, 2007
[Papadimitriou]
Christos H. Papadimitriou. Computational Complexity. Addison Wesley Publ. Co., Reading, Massachussetts, 1994.
[Complexity]
Complexity Results and Practical Algorithms for Logics in Knowledge Representation. Stephan Tobies. Ph.D Dissertation, 2002
[DLP]
Description Logic Programs: Combining Logic Programs with Description Logic. Benjamin N. Grosof, Ian Horrocks, Raphael Volz, and Stefan Decker. in Proc. of the 12th Int. World Wide Web Conference (WWW 2003), Budapest, Hungary, 2003. pp.: 48–57
[pD*]
Completeness, decidability and complexity of entailment for RDF Schema and a semantic extension involving the OWL vocabulary. Herman J. ter Horst. J. of Web Semantics 3(2–3):79–115, 2005
[RIF]
RIF RDF and OWL Compatibility. Jos de Bruijn, ed. W3C Working Draft 30 July 2008
[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
[SNOMED CT]
Systematized Nomenclature of Medicine – Clinical Terms. International Health Terminology Standards Development Organization (IHTSDO)