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### OWL2：OWL的下一步发展 #### 概述与背景自从2004年成为W3C推荐标准以来，Web本体语言（OWL）在计算机科学领域得到了广泛的应用。尽管总体上对OWL的实际应用反馈是积极的，但也暴露了一些需要改进的地方。为了系统地分析OWL存在的不足之处，并提出解决方案，本文作者Bernardo Cuenca Grau、Ian Horrocks、Boris Motik、Bijan Parsia、Peter Patel-Schneider以及Ulrike Sattler，分别来自牛津大学、曼彻斯特大学和贝尔实验室研究部，共同撰写了这篇文章。 #### 问题分析与改进方向 ##### 表达能力问题 OWL在表达能力方面存在一定的局限性，这主要体现在无法处理某些复杂的关系和属性约束。例如，OWL Lite和OWLDL对于属性链的处理有限，而这些链对于表示复杂的本体关系是非常重要的。此外，OWL Full虽然提供了更强大的表达能力，但其推理过程却非常复杂且难以控制。 ##### 语法问题 OWL的语法设计也存在一些不足之处，如RDF/XML语法的冗余性和不易读性。这些问题不仅影响了开发人员的使用体验，还可能引入不必要的错误。 ##### 物种定义缺陷 OWL物种的定义也有待完善。OWL Lite、OWLDL和OWL Full三种版本之间的差异较大，导致用户在选择适合自身需求的语言版本时面临困难。此外，不同版本之间兼容性较差，使得迁移成本较高。 #### OWL2的特性与改进为了解决上述问题，W3C OWL工作组正在开发OWL2，这是一个对OWL进行了扩展和修订的新版本。OWL2在许多方面进行了彻底的重新设计，旨在提供一个更为健壮的语言平台，支持未来的进一步发展。 ##### 增强的表达能力 OWL2在保持与现有OWL版本兼容的同时，增强了表达能力。例如，引入了新的构造来更好地处理属性链，支持更复杂的属性限制，并增强了对匿名个体的支持等。 ##### 改进的语法为了提高可读性和可用性，OWL2对其语法进行了优化。它采用了更简洁的语法结构，同时保持了与RDF/XML语法的一致性。此外，还引入了更易于理解的缩写形式，使得编写和维护本体更加简便。 ##### 更清晰的物种定义 OWL2重新定义了其物种概念，使其更符合实际应用需求。它通过引入新的语言级别（如OWL2 RL和OWL2 QL），更好地平衡了表达能力和推理效率之间的关系。这些新级别的设计考虑到了特定应用场景的需求，从而使得OWL2能够更好地服务于不同的用户群体。 ##### 其他改进除了上述改进之外，OWL2还引入了许多其他功能和优化措施。例如，增加了对规则的支持，允许用户定义更复杂的逻辑关系；提高了与其他语言（如SPARQL）的互操作性；并加强了安全性方面的考虑等。 #### 结论与展望 OWL2是基于多年实践经验积累的基础上对OWL进行的重大升级。通过对原有问题的深入分析和针对性改进，OWL2不仅解决了之前的不足之处，还进一步增强了其作为语义网核心组成部分的地位。未来，随着更多创新特性的加入和技术进步，OWL2有望成为构建智能应用程序和服务的强大工具之一。

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OWL 2: The Next Step for OWL

Bernardo Cuenca Grau

, Ian Horrocks

, Boris Motik

, Bijan Parsia

Peter Patel-Schneider

, Ulrike Sattler

University of Oxford, Oxford, UK

University of Manchester, Manchester, UK

Bell Labs Research, New Jersey, USA

Abstract

Since achieving W3C recommendation status in 2004, the Web Ontology Language (OWL) has been successfully

applied to many problems in computer science. Practical experience with OWL has been quite positive in general;

however, it has also revealed room for improvement in several areas. We systematically analyze the identiﬁed short-

comings of OWL, such as expressivity issues, problems with its syntaxes, and deﬁciencies in the deﬁnition of OWL

species. Furthermore, we present an overview of OWL 2—an extension to and revision of OWL that is currently be-

ing developed within the W3C OWL Working Group. Many aspects of OWL have been thoroughly reengineered in

OWL 2, thus producing a robust platform for future development of the language.

Key words: Ontologies, Ontology Languages, Semantic Web

1. Introduction

Since the inception of the Semantic Web, the de-

velopment of languages for modeling ontologies—

conceptualizations of a domain shared by a commu-

nity of users—has been seen as a key task. The initial

proposals focused on RDF and RDF Schema; how-

ever, these languages were soon found to be too lim-

ited in expressive power [18]. The World Wide Web

Consortium (W3C) therefore formed the Web On-

tology Working Group, whose goal was to develop

an expressive language suitable for application in

the Semantic Web. The result of this endeavor was

Email addresses:

bernardo.cuenca.grau@comlab.ox.ac.uk (Bernardo

Cuenca Grau), ian.horrocks@comlab.ox.ac.uk (Ian

Horrocks), boris.motik@comlab.ox.ac.uk (Boris Motik),

bparsia@cs.man.ac.uk (Bijan Parsia),

pfps@research.bell-labs.com (Peter Patel-Schneider),

sattler@cs.man.ac.uk (Ulrike Sattler).

the OWL Web Ontology Language, which became

a W3C recommendation in February 2004. OWL is

actually a family of three language variants (often

called species) of increasing expressive power: OWL

Lite, OWL DL, and OWL Full [28].

The standardization of OWL has sparked the de-

velopment and/or adaption of a number of reason-

ers, including FacT++ [37], Pellet [32], RACER [11],

and HermiT [26], and ontology editors, including

Prot´eg´e

and Swoop [21]. OWL ontologies are being

developed in areas as diverse as e-Science, medicine,

biology, geography, astronomy, defense, and the au-

tomotive and aerospace industries. OWL is exten-

sively used in the life sciences community, where it

has rapidly become a de facto standard for ontology

development and data interchange; for example, see

BioPAX,

NASA’s SWEET ontologies,

and the

http://protege.stanford.edu/

http://www.biopax.org/

http://sweet.jpl.nasa.gov/ontology/

Preprint submitted to Else vier 8 November 2008

National Cancer Institute Thesaurus.

Despite the success story surrounding OWL, the

numerous contexts in which the language has been

applied have revealed some deﬁciencies in the orig-

inal design. In Section 2, we present a systematic

analysis of problems identiﬁed by OWL users and

the designers of OWL tools such as editors and rea-

soners. For example, ontology engineers developing

ontologies for biomedical applications have identi-

ﬁed signiﬁcant expressivity limitations of the lan-

guage. Also, the designers of OWL APIs have iden-

tiﬁed several practical limitations such as diﬃculties

in parsing OWL ontologies or the inability to check

for obvious errors, such as mistyped names.

In response to users’ comments and requests, the

idea was born to address some of these needs via an

incremental revision of OWL, provisionally called

OWL 1.1. The initial goal of OWL 1.1 was to ex-

ploit recent developments in DL research in order to

address some of the expressivity limitations of the

language. After extensive discussions at the 2005

OWL Experiences and Directions Workshop,

consensus was reached regarding the new features

to be provided by OWL 1.1. This set of new features

roughly corresponds to the intersection of what

users wanted, what theoreticians said was possible,

and what implementors believed was practicable.

As the design of OWL 1.1 progressed, it was de-

cided to also take the opportunity to “clean up”

the language and its speciﬁcation, so as to provide

a more robust platform for future development.

The development of OWL 1.1 was initially under-

taken by an informal group of language users and

developers. After the original speciﬁcation reached

a mature state and ﬁrst implementations were re-

leased, the OWL 1.1 proposal was submitted to the

W3C as a Member Submission

with the inten-

tion of using it as a starting point for a new W3C

Working Group. The Working Group was oﬃcially

formed in September 2007. As the work on the new

language progressed, the initial Member Submis-

sion evolved signiﬁcantly. Consequently, the Work-

ing Group eventually decided in April 2008 to call

the new language OWL 2 and so indicate a substan-

tial step in the evolution of the language.

In Section 3, we present the design of OWL 2 and

discuss how it addresses the drawbacks of OWL 1

that we identiﬁed in Section 2. We discuss diﬀer-

http://www.nci.nih.gov/

http://www.mindswap.org/2005/OWLWorkshop/

http://www.w3.org/Submission/2006/10/

ent aspects of the language, such as its expressivity,

syntax, speciﬁcation style, and various metalogical

features. In Section 4 we discuss the current state

of implementation, and conclude in Section 5 with

a discussion of possible future extensions. To avoid

any ambiguity, we refer to the initial version of OWL

as OWL 1 in the rest of this paper.

2. Why Go Beyond OWL 1?

Although, or even perhaps because, OWL 1 has

been successful, certain problems have been identi-

ﬁed in its design. None of these problems are severe,

but, taken together, they indicate a need for a re-

vision of OWL 1. In this section, we discuss what

these problems are.

2.1. Expressivity Limitations

Practical experience with OWL 1 has shown that

OWL 1 DL—the most expressive but still decidable

language of the OWL 1 family—lacks several con-

structs that are often necessary for modeling com-

plex domains [31,30]. As a response, the community

of OWL 1 users and application designers developed

various patterns for approximating the missing con-

structs.

Since the actual expressive power is miss-

ing, these workarounds are often unsound or incom-

plete with respect to the intended semantics. Fur-

thermore, it is usually diﬃcult, if not impossible, to

identify all the cases in which these patterns yield in-

correct results. Such patterns are therefore not only

cumbersome but also of limited utility, and extend-

ing the language with the missing constructs seems

to be the only satisfactory solution to the problem.

2.1.1. Qualiﬁed Cardinality Restrictions

The existential restrictions of OWL 1 DL allow

the restriction to be qualiﬁed with a class; for ex-

ample, one can deﬁne a class such as “persons that

have at least one child who is male.” Cardinality re-

strictions, however, cannot be qualiﬁed with a class;

thus, OWL 1 DL allows for the deﬁnition of a person

with at least three children, but not of a person with

at least three children who are male. Expressing the

latter class requires the restriction to be qualiﬁed

with respect to the class (i.e., male) to which the

objects being counted (i.e., children) belong. This

http://www.w3.org/2001/sw/BestPractices/OEP/

feature is typically called a qualiﬁed cardinality re-

striction (QCR).

Ontology modelers have repeatedly identiﬁed the

importance of QCRs in various modeling problems.

For example, one may want to deﬁne a quadruped

as an animal with exactly four parts that are legs,

or a medical oversight committee as a committee

that consists of at least ﬁve members, of which two

are medically qualiﬁed, one is a manager, and two

are members of the public [30]. In OWL 1, quali-

ﬁed cardinality restrictions are commonly approx-

imated using design patterns discussed in [30,40];

however, these workarounds are often unsound, or

incomplete, or both.

At the time the Web Ontology Working Group

was designing OWL 1, it was already known that

QCRs can be added to the language without aﬀect-

ing its computational properties, both from a the-

oretical and from an implementation point of view;

in fact, QCRs were included in DAML+OIL—a lan-

guage that served as the basis for OWL 1 [18]. The

ﬁnal decision was, however, not to include this par-

ticular feature in the language due to concerns about

user understandability.

2.1.2. Relational Expressivity

While OWL 1 provides a wide range of construc-

tors for building complex classes, relatively little can

be said about properties. Ontology modelers have

repeatedly asked for greater relational expressivity

(i.e., expressivity about properties), and the lack of

this expressivity has been identiﬁed as a major im-

pediment for the adoption of OWL 1. We will illus-

trate this point with two prominent use cases.

Propagation along properties. Applications com-

monly need to model interactions that are some-

times described as one property “propagating” or

being “transitive across” another. Use cases abound

in the life sciences domain, where one often needs

to describe interactions between locative properties

and various kinds of part-whole properties [29]. For

example, we might want to assert that an abnormal-

ity of a part of an anatomical structure constitutes

an abnormality of the structure as a whole [29].

This allows us to draw many useful inferences, such

as inferring that a fracture of the neck of the femur

is a kind of fracture of the femur, or that an ulcer

located in the gastric mucosa is a kind of stomach

ulcer. Languages speciﬁcally designed for use in life

sciences such as OBO

and SNOMED

commonly

provide for such features, even though they typically

support a much smaller set of class constructors

than OWL 1. Thus, supporting transitive propaga-

tion of roles in OWL seemed vital if OWL were to

gain widespread acceptance in the life sciences.

Properties of properties. In mereology—the philo-

sophic study of parts and wholes—the partOf rela-

tion is often speciﬁed to be transitive (if x is a part

of y and y is a part of z, then x is a part of z), reﬂex-

ive (every object is a part of itself), and asymmet-

ric (nothing is a part of one of its parts). Many ap-

plications that describe complex structures (such as

life science and engineering applications) extensively

use part-whole relations axiomatized according to

these principles. Other types of properties with dif-

ferent axiomatizations are often found in practice

(see, e.g., the OBO Relations Ontology

), such as

locative relations (typically transitive and reﬂexive),

causal relations (typically transitive and irreﬂexive),

and membership relations (typically irreﬂexive).

At the time OWL 1 DL became a W3C recom-

mendation, it was not known whether the language

could be augmented with such features (apart from

transitivity) without giving up the decidability of

key inference problems, much less whether it would

be possible to develop practical reasoning proce-

dures for such extensions. Consequently, such fea-

tures were excluded from OWL 1. As in the case of

QCRs, users have developed modeling patterns in-

tended to approximate the missing features, which

has often lead to problems in practice.

2.1.3. Datatype Expressivity

OWL 1 provides very limited expressive power for

describing classes whose instances are related to con-

crete values such as integers and strings. In OWL

1, it is possible to express restrictions on datatype

properties qualiﬁed by a unary datatype. For ex-

ample, one could state that every British citizen

must have a passport number which is an xsd:string,

where the latter is an XML Schema datatype—a

unary predicate interpreted as the set of all string

values. In OWL 1, however, it is not possible to rep-

resent the following kinds of statements:

http://obo.sourceforge.net/

http://www.snomed.org/

http://www.obofoundry.org/

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rorygo

2013-11-06

没什么用，介绍型的文档，写论文的时候可以参考

dianazhao

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