(摘录) (ASWP) Chap 4 Web Ontology Language: OWL-优快云博客

本文详细介绍了OWL语言的主要特性，包括语法形式、类元素、属性元素、限制条件及特殊属性等内容，并对比了OWL Full、OWL DL与OWL Lite的不同之处。

4 Web Ontology Language: OWL

4.1 Introduction

1 Main requirements for ontology language

a well-defined syntax

efficient reasoning support

a formal semantics

sufficient expressive power

convenience of expression

2 Mapping to a known logical formalism

A Formal semantics and reasoning support are usually provided by mapping an ontology language to a known logical formalism, and by using automated reasoners that already exist for those formalisms.

OWL is (partially) mapped on a description logic, and makes use of existing reasoners such as FaCT and RACER.

3 Limitations of the Expressive Power of RDF Schema

local scope of properties

In RDF Schema we cannot declare range restrictions that apply to some classes only. For example, we cannot say that cows eat only plants, while other animals may eat meat, too.

Disjointness of classes

不能指定两个类(如male和female)没有交集.

Boolean combinations of classes

无法通过交,联合,补等集合操作来定义新的类.

Cardinality restrictions

不能指定一个属性可以有或应该有几个值.

Special characteristics of properties

不能指定a property is transitive, unique, inverse of another property

4. Comparison between OWL language Species

OWL Full

OWL DL

OWL Lite

Expressive power

High

Medium

Low

uses all the OWL languages primitives. It also allows the combination of these primitives in arbitrary ways with RDF and RDF Schema.

essentially application of OWL’s constructor’s to each other is disallowed, thus ensuring that the language corresponds to a well studied description logic.

Reasoning support

Low

Medium

Hign

Upward-compatibility with RDF

Any legal RDF document is also a legal OWL Full document;

Any valid RDF/RDF Schema conclusion is also a valid OWL Full conclusion.

An RDF document

will in general have to be extended in some ways and restricted in others

before it is a legal OWL DL document. Every legal OWL DL document is a

legal RDF document.

5. upward compatibility between these three sublanguages

• Every legal OWL Lite ontology is a legal OWL DL ontology.

• Every legal OWL DL ontology is a legal OWL Full ontology.

• Every valid OWL Lite conclusion is a valid OWL DL conclusion.

• Every valid OWL DL conclusion is a valid OWL Full conclusion.

6. OWL still uses RDF and RDF Schema to a large extent

• All varieties of OWL use RDF for their syntax.

• Instances are declared as in RDF, using RDF descriptions and typing information.

• OWL constructors like owl:Class, and owl:DatatypeProperty, and owl:ObjectProperty are specialisations of their RDF counterparts.

7. Full downward compatibility for OWL

The advantage of full downward compatibility for OWL (that any OWL-aware processor will also provide correct interpretations of any RDF Schema document) is only achieved for OWL Full, at the cost of computational intractability.

4.2 The OWL Language

1. Syntactic form for OWL language

(1) RDF/XML(primary, we use it in this book)

(2) An XML-based syntax5 that does not follow the RDF conventions and is thus more easily read by human users.

(3) An abstract syntax, used in the language specification document.

(4) A graphic syntax based on the conventions of UML.

2. Class Elements

subclass

<owl:Class rdf:ID="associateProfessor">

<rdfs:subClassOf rdf:resource="#academicStaffMember"/>

</owl:Class>

disjoint

<owl:Class rdf:about="#associateProfessor">

<owl:disjointWith rdf:resource="#professor"/>

<owl:disjointWith rdf:resource="#assistantProfessor"/>

</owl:Class>

equivalent

<owl:Class rdf:ID="faculty">

<owl:equivalentClass rdf:resource="#academicStaffMember"/>

</owl:Class>

There are two predefined classes, owl:Thing and owl:Nothing.

The former is the most general class, which contains everything (everything is a thing), and the latter is the empty class. Thus every class is a subclass of owl:Thing and a superclass of owl:Nothing.

3. Property Elements

Type of Properties

(1) Object Property

对象之间的关系,比如Teach

<owl:ObjectProperty rdf:ID="isTaughtBy">

<rdfs:domain rdf:resource="#course"/>

<rdfs:range rdf:resource="#academicStaffMember"/>

<rdfs:subPropertyOf rdf:resource="#involves"/>

</owl:ObjectProperty>

(2) Data type Property

属性,比如phone

<owl:DatatypeProperty rdf:ID="age">

<rdfs:range rdf:resource="http://www.w3.org/2001/XMLSchema

#nonNegativeInteger"/>

</owl:DatatypeProperty>

4. Property Restrictions

(universal quantification) Requires first-year courses to be taught by professors only

<owl:Class rdf:about="#firstYearCourse">

<rdfs:subClassOf>

<owl:Restriction>

<owl:onProperty rdf:resource="#isTaughtBy"/>

<owl:allValuesFrom rdf:resource="#Professor"/>

</owl:Restriction>

</rdfs:subClassOf>

</owl:Class>

(existential quantification) All academic staff members must teach at least one undergraduate course

<owl:Class rdf:about="#academicStaffMember">

<rdfs:subClassOf>

<owl:Restriction>

<owl:onProperty rdf:resource="#teaches"/>

<owl:someValuesFrom rdf:resource="#undergraduateCourse"/>

</owl:Restriction>

</rdfs:subClassOf>

</owl:Class>

defines cardinality restrictions

<owl:Class rdf:about="#course">

<rdfs:subClassOf>

<owl:Restriction>

<owl:onProperty rdf:resource="#isTaughtBy"/>

<owl:minCardinality rdf:datatype="&xsd;nonNegativeInteger">

</owl:minCardinality>

</owl:Restriction>

</rdfs:subClassOf>

</owl:Class>

owl:Restriction defines an anonymous class which has no ID, is not defined by owl:Class, and has only local scope: it can only be used in the one place where the restriction appears.