OWL 2 Web Ontology Language Profiles (Second Edition) (original) (raw)

W3C

W3C Recommendation 11 December 2012

This version:

http://www.w3.org/TR/2012/REC-owl2-profiles-20121211/

Latest version (series 2):

http://www.w3.org/TR/owl2-profiles/

Latest Recommendation:

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

Previous version:

http://www.w3.org/TR/2012/PER-owl2-profiles-20121018/

Editors:

Boris Motik, University of Oxford

Bernardo Cuenca Grau, University of Oxford

Ian Horrocks, University of Oxford

Zhe Wu, Oracle

Achille Fokoue, IBM Corporation

Carsten Lutz, University of Bremen

Contributors: (in alphabetical order)

Diego Calvanese, Free University of Bozen-Bolzano

Jeremy Carroll, HP (now at TopQuadrant)

Giuseppe De Giacomo, Sapienza Università di Roma

Jim Hendler, Rensselaer Polytechnic Institute

Ivan Herman, W3C/ERCIM

Bijan Parsia, University of Manchester

Peter F. Patel-Schneider, Nuance Communications

Alan Ruttenberg, Science Commons (Creative Commons)

Uli Sattler, University of Manchester

Michael Schneider, FZI Research Center for Information Technology

Please refer to the errata for this document, which may include some normative corrections.

A color-coded version of this document showing changes made since the previous version is also available.

This document is also available in these non-normative formats: PDF version.

See also translations.

Copyright © 2012 W3C® (MIT, ERCIM, Keio), All Rights Reserved. W3C liability, trademark and document use rules apply.

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

May Be Superseded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/.

Summary of Changes

Please Send Comments

Please send any comments to public-owl-comments@w3.org (public archive). Although work on this document by the OWL Working Group is complete, comments may be addressed in the errata or in future revisions. Open discussion among developers is welcome at public-owl-dev@w3.org (public archive).

Endorsed By W3C

This document has been reviewed by W3C Members, by software developers, and by other W3C groups and interested parties, and is endorsed by the Director as a W3C Recommendation. It is a stable document and may be used as reference material or cited from another document. W3C's role in making the Recommendation is to draw attention to the specification and to promote its widespread deployment. This enhances the functionality and interoperability of the Web.

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.

Table of Contents

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 profiles are independent of each other, so (prospective) users can skip over the descriptions of profiles that are not of interest to them. The choice of which profile to use in practice will depend on the structure of the ontologies and the reasoning tasks at hand (see Section 10 of the OWL 2 Primer [OWL 2 Primer] for more help in understanding and selecting profiles).

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. Note that none of the profiles is a subset of another.

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].

2 OWL 2 EL

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

For example, OWL 2 EL provides class constructors that are sufficient to express the very large 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:

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

The following constructs are not supported in OWL 2 EL:

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:

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: 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

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 is designed so that sound and complete query answering is in LOGSPACE (more precisely, in AC0) 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 DL. It is designed so that data (assertions) that is stored in a standard relational database system can be queried through an ontology via a simple rewriting mechanism, i.e., by rewriting the query into an SQL query that is then answered by the RDBMS system, without any changes to the data.

OWL 2 QL is based on the DL-Lite family of description logics [DL-Lite]. Several variants of DL-Lite have been described in the literature, 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.

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 intersection (ObjectIntersectionOf) negation (ObjectComplementOf) existential quantification to a class (ObjectSomeValuesFrom) existential quantification to a data range (DataSomeValuesFrom)

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

The following constructs are not supported in OWL 2 QL:

OWL 2 QL does not support individual equality assertions (SameIndividual): adding such axioms to OWL 2 QL would increase the data complexity of query answering, so that it is no longer first order rewritable, which means that query answering could not be implemented directly using relational database technologies. However, an ontology O that includes individual equality assertions, but is otherwise OWL 2 QL, could be handled by computing the reflexive–symmetric–transitive closure of the equality (SameIndividual) relation in O (this requires answering recursive queries and can be implemented in LOGSPACE w.r.t. the size of data) [DL-Lite-bool], and then using this relation in query answering procedures to simulate individual equality reasoning [Automated Reasoning].

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:

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: 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 and transitive 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 |
ReflexiveObjectProperty |
SymmetricObjectProperty | AsymmetricObjectProperty

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 individual 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 key axioms are not allowed.

Axiom := Declaration | ClassAxiom | ObjectPropertyAxiom | DataPropertyAxiom | DatatypeDefinition | 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 was 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 (e.g., one based on the partial axiomatization presented in Section 4.3) will have desirable computational properties; for example, it can return all and only the correct answers to certain kinds of query (see Theorem PR1 and OWL 2 Conformance [OWL 2 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. Such an implementation will, however, still produce only correct entailments (see OWL 2 Conformance [OWL 2 Conformance]).

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 expression (ObjectSomeValuesFrom) existential quantification to a data range (DataSomeValuesFrom) existential quantification to an individual (ObjectHasValue) existential quantification to a literal (DataHasValue) a class other than owl:Thing intersection of classes (ObjectIntersectionOf) negation (ObjectComplementOf) universal quantification to a class expression (ObjectAllValuesFrom) existential quantification to an individual (ObjectHasValue) at-most 0/1 cardinality restriction to a class expression (ObjectMaxCardinality 0/1) universal quantification to a data range (DataAllValuesFrom) existential quantification to a literal (DataHasValue) at-most 0/1 cardinality restriction to a data range (DataMaxCardinality 0/1)

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) and reflexive object property axioms (ReflexiveObjectProperty).

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 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:

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

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 class expressions 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 | superObjectComplementOf |
superObjectAllValuesFrom | ObjectHasValue | superObjectMaxCardinality |
DataAllValuesFrom | DataHasValue | superDataMaxCardinality
superObjectIntersectionOf := 'ObjectIntersectionOf' '(' superClassExpression superClassExpression { superClassExpression } ')'
superObjectComplementOf := 'ObjectComplementOf' '(' subClassExpression ')'
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 differences being that class expressions in property domain and range axioms are restricted to superClassExpression, and that the use of reflexive properties is disallowed.

ObjectPropertyDomain := 'ObjectPropertyDomain' '(' axiomAnnotations ObjectPropertyExpression superClassExpression ')'
ObjectPropertyRange := 'ObjectPropertyRange' '(' axiomAnnotations ObjectPropertyExpression superClassExpression ')'
DataPropertyDomain := 'DataPropertyDomain' '(' axiomAnnotations DataPropertyExpression superClassExpression ')'
ObjectPropertyAxiom :=
SubObjectPropertyOf | EquivalentObjectProperties |
DisjointObjectProperties | InverseObjectProperties |
ObjectPropertyDomain | ObjectPropertyRange |
FunctionalObjectProperty | InverseFunctionalObjectProperty |
IrreflexiveObjectProperty |
SymmetricObjectProperty | AsymmetricObjectProperty
TransitiveObjectProperty

OWL 2 RL restricts class expressions in positive assertions to superClassExpression. All other assertions are the same as in the structural specification [OWL 2 Specification].

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

OWL 2 RL restricts class expressions in keys to subClassExpression.

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

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 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 such as logic programming [Logic Programming, Lloyd].

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 RDF & OWL]); 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 rules that have empty "if" parts should be understood as being always applicable. 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. The rows of several tables specify rules that need to be instantiated for each combination of indices given in the right-most column.

Table 4 axiomatizes the semantics of equality. In particular, it defines the equality relation 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(?x, rdf:type, owl:AllDifferent) T(?x, owl:members, ?y) LIST[?y, ?z1, ..., ?zn] T(?zi, owl:sameAs, ?zj) | false | for each 1 ≤ i < j ≤ n | | eq-diff3 | T(?x, rdf:type, owl:AllDifferent) T(?x, owl:distinctMembers, ?y) LIST[?y, ?z1, ..., ?zn] T(?zi, owl:sameAs, ?zj) | 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 | | 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(?p, owl:propertyChainAxiom, ?x) LIST[?x, ?p1, ..., ?pn] 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(?x, rdf:type, owl:AllDisjointProperties) T(?x, owl:members, ?y) LIST[?y, ?p1, ..., ?pn] T(?u, ?pi, ?v) T(?u, ?pj, ?v) | 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) | | | prp-npa1 | T(?x, owl:sourceIndividual, ?i1) T(?x, owl:assertionProperty, ?p) T(?x, owl:targetIndividual, ?i2) T(?i1, ?p, ?i2) | false | | | prp-npa2 | T(?x, owl:sourceIndividual, ?i) T(?x, owl:assertionProperty, ?p) T(?x, owl:targetValue, ?lt) T(?i, ?p, ?lt) | false | |

Table 6 specifies the semantic conditions on classes.

Table 6. The Semantics of Classes

| | If | then | | | | ------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | ------------------------------------------------------------------ | ------------------ | | cls-thing | | T(owl:Thing, rdf:type, owl:Class) | | | cls-nothing1 | | 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-com | T(?c1, owl:complementOf, ?c2) T(?x, rdf:type, ?c1) T(?x, rdf:type, ?c2) | false | | | 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(?y1, rdf:type, ?c) ... T(?yn, rdf:type, ?c) | |

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(?x, rdf:type, owl:AllDisjointClasses) T(?x, owl:members, ?y) LIST[?y, ?c1, ..., ?cn] T(?z, rdf:type, ?ci) T(?z, 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 | | T(dt, rdf:type, rdfs:Datatype) | for each datatype dt supported in OWL 2 RL | | dt-type2 | | 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 | | T(lt1, owl:sameAs, lt2) | for all literals lt1 and lt2 with the same data value | | dt-diff | | 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 (i.e., those triples that must be satisfied by, respectively, every RDF and RDFS interpretation) [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 [OWL 2 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:

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 A ∈ O2 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 complexity measures are considered:

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:

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 N2EXPTIME-complete (NEXPTIME-complete if the property hierarchy can be translated into a polynomially-sized nondeterministic finite automaton) Decidable, but complexity open(NP-Hard) Not Applicable N2EXPTIME-complete (NEXPTIME-complete if the property hierarchy can be translated into a polynomially-sized nondeterministic finite automaton)
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 in EXPTIME (PTIME-complete if the property hierarchy can be translated into a polynomially-sized nondeterministic finite automaton) PTIME-complete NP-complete in EXPTIME (PSPACE-complete if the property hierarchy can be translated into a polynomially-sized nondeterministic finite automaton)
OWL 2 QL Ontology Consistency, Class Expression Satisfiability, Class Expression Subsumption, Instance Checking NLogSpace-complete In AC0 Not Applicable NLogSpace-complete
Conjunctive Query Answering NLogSpace-complete In AC0 NP-complete NP-complete
OWL 2 RL Ontology Consistency PTIME-complete PTIME-complete Not Applicable PTIME-complete
Class Expression Satisfiability, Class Expression Subsumption, Instance Checking PTIME-complete PTIME-complete Not Applicable co-NP-complete (PTIME-complete for atomic class expressions)
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 | stringLiteralNoLanguage | stringLiteralWithLanguage
typedLiteral := lexicalForm '^^' Datatype
lexicalForm := quotedString
stringLiteralNoLanguage := quotedString
stringLiteralWithLanguage := 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 | DatatypeDefinition | 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 ')'

DatatypeDefinition := 'DatatypeDefinition' '(' axiomAnnotations Datatype DataRange ')'

HasKey := 'HasKey' '(' axiomAnnotations ClassExpression '(' { 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 | stringLiteralNoLanguage | stringLiteralWithLanguage
typedLiteral := lexicalForm '^^' Datatype
lexicalForm := quotedString
stringLiteralNoLanguage := quotedString
stringLiteralWithLanguage := quotedString languageTag

ObjectPropertyExpression := ObjectProperty | InverseObjectProperty

InverseObjectProperty := 'ObjectInverseOf' '(' ObjectProperty ')'

DataPropertyExpression := DataProperty

DataRange := Datatype | DataIntersectionOf

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

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 ')'

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

Axiom := Declaration | ClassAxiom | ObjectPropertyAxiom | DataPropertyAxiom | DatatypeDefinition | 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 |
ReflexiveObjectProperty |
SymmetricObjectProperty | AsymmetricObjectProperty

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

DatatypeDefinition := 'DatatypeDefinition' '(' axiomAnnotations Datatype DataRange ')'

Assertion := DifferentIndividuals | ClassAssertion | ObjectPropertyAssertion | DataPropertyAssertion

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

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

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

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

DataPropertyAssertion := 'DataPropertyAssertion' '(' 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 | stringLiteralNoLanguage | stringLiteralWithLanguage
typedLiteral := lexicalForm '^^' Datatype
lexicalForm := quotedString
stringLiteralNoLanguage := quotedString
stringLiteralWithLanguage := quotedString languageTag

ObjectPropertyExpression := ObjectProperty | InverseObjectProperty

InverseObjectProperty := 'ObjectInverseOf' '(' ObjectProperty ')'

DataPropertyExpression := DataProperty

DataRange := Datatype | DataIntersectionOf

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

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 | superComplementOf |
superObjectAllValuesFrom | ObjectHasValue | superObjectMaxCardinality |
DataAllValuesFrom | DataHasValue | superDataMaxCardinality

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

superObjectComplementOf := 'ObjectComplementOf' '(' subClassExpression ')'

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 } ')'

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

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

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

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

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

Axiom := Declaration | ClassAxiom | ObjectPropertyAxiom | DataPropertyAxiom | DatatypeDefinition | 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 := 'SubObjectPropertyOf' '(' axiomAnnotations subObjectPropertyExpression superObjectPropertyExpression ')'
subObjectPropertyExpression := ObjectPropertyExpression | propertyExpressionChain
propertyExpressionChain := 'ObjectPropertyChain' '(' ObjectPropertyExpression ObjectPropertyExpression { ObjectPropertyExpression } ')'
superObjectPropertyExpression := ObjectPropertyExpression

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

DatatypeDefinition := 'DatatypeDefinition' '(' axiomAnnotations Datatype DataRange ')'

HasKey := 'HasKey' '(' axiomAnnotations subClassExpression '(' { 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 superClassExpression 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 ')'

7 Appendix: Change Log (Informative)

7.1 Changes Since Recommendation

This section summarizes the changes to this document since the Recommendation of 27 October, 2009.

7.2 Changes Since Proposed Recommendation

No changes have been made to this document since the Proposed Recommendation of 22 September, 2009.

7.3 Changes Since Candidate Recommendation

This section summarizes the changes to this document since the Candidate Recommendation of 11 June, 2009.

7.4 Changes Since Last Call

This section summarizes the changes to this document since the Last Call Working Draft of 21 April, 2009.

8 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 Jie Bao (RPI), 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.

9 References

9.1 Normative References

[OWL 2 Conformance]

OWL 2 Web Ontology Language: Conformance (Second Edition) Michael Smith, Ian Horrocks, Markus Krötzsch, Birte Glimm, eds. W3C Recommendation, 11 December 2012, http://www.w3.org/TR/2012/REC-owl2-conformance-20121211/. Latest version available at http://www.w3.org/TR/owl2-conformance/.

[OWL 2 Direct Semantics]

OWL 2 Web Ontology Language: Direct Semantics (Second Edition) Boris Motik, Peter F. Patel-Schneider, Bernardo Cuenca Grau, eds. W3C Recommendation, 11 December 2012, http://www.w3.org/TR/2012/REC-owl2-direct-semantics-20121211/. Latest version available at http://www.w3.org/TR/owl2-direct-semantics/.

[OWL 2 RDF Mapping]

OWL 2 Web Ontology Language: Mapping to RDF Graphs (Second Edition) Peter F. Patel-Schneider, Boris Motik, eds. W3C Recommendation, 11 December 2012, http://www.w3.org/TR/2012/REC-owl2-mapping-to-rdf-20121211/. Latest version available at http://www.w3.org/TR/owl2-mapping-to-rdf/.

[OWL 2 RDF-Based Semantics]

OWL 2 Web Ontology Language: RDF-Based Semantics (Second Edition) Michael Schneider, editor. W3C Recommendation, 11 December 2012, http://www.w3.org/TR/2012/REC-owl2-rdf-based-semantics-20121211/. Latest version available at http://www.w3.org/TR/owl2-rdf-based-semantics/.

[OWL 2 Specification]

OWL 2 Web Ontology Language: Structural Specification and Functional-Style Syntax (Second Edition) Boris Motik, Peter F. Patel-Schneider, Bijan Parsia, eds. W3C Recommendation, 11 December 2012, http://www.w3.org/TR/2012/REC-owl2-syntax-20121211/. Latest version available at http://www.w3.org/TR/owl2-syntax/.

[RFC 2119]

RFC 2119: Key words for use in RFCs to Indicate Requirement Levels. Network Working Group, S. Bradner. IETF, March 1997, http://www.ietf.org/rfc/rfc2119.txt

9.2 Nonnormative References

[Complexity]

Complexity Results and Practical Algorithms for Logics in Knowledge Representation. Stephan Tobies. Ph.D Dissertation, 2002

[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

[DL-Lite-bool]

The DL-Lite Family and Relatives. Alessandro Artale, Diego Calvanese, Roman Kontchakov, Michael Zakharyaschev, submitted.

[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

[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

[OWL 1 Reference]

OWL Web Ontology Language Reference. Mike Dean and Guus Screiber, eds., W3C Recommendation, 10 February 2004.

[OWL 2 Primer]

OWL 2 Web Ontology Language: Primer (Second Edition) Pascal Hitzler, Markus Krötzsch, Bijan Parsia, Peter F. Patel-Schneider, Sebastian Rudolph, eds. W3C Recommendation, 11 December 2012, http://www.w3.org/TR/2012/REC-owl2-primer-20121211/. Latest version available at http://www.w3.org/TR/owl2-primer/.

[Papadimitriou]

Christos H. Papadimitriou. Computational Complexity. Addison Wesley Publ. Co., Reading, Massachussetts, 1994.

[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

[RDF Semantics]

RDF Semantics. Patrick Hayes, ed., W3C Recommendation, 10 February 2004, http://www.w3.org/TR/2004/REC-rdf-mt-20040210/. Latest version available as http://www.w3.org/TR/rdf-mt/.

[RIF RDF & OWL]

RIF RDF and OWL Compatibility. Jos de Bruijn, ed., W3C Working Draft, 30 July 2008.

[SNOMED CT]

Systematized Nomenclature of Medicine – Clinical Terms. International Health Terminology Standards Development Organization (IHTSDO)

[Automated Reasoning]

Handbook of Automated Reasoning. A. Robinson and A. Voronkov, eds., Elsevier Science, 2001

[Logic Programming]

Logic programming and knowledge representation. Chitta Baral and Michael Gelfond. Journal of Logic Programming 19:73–148, 1994.

[Lloyd]

Foundations of Logic Programming, 2nd ed. John Wylie Lloyd. Springer-Verlag, Berlin, Germany, 1987.