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Chapter 7.21
A Basis for the Semantic Web and E-Business:
(IۋFLHQW2UJDQL]DWLRQRI2QWRORJLanguages and Ontologies
Changqing Li
National University of Singapore, Singapore
Tok Wang Ling
National University of Singapore, Singapore
ABSTRACT
This chapter introduces how to effectively orga-nize ontology languages and ontologies and how WRHI¿FLHQWO\SURFHVVVHPDQWLFLQIRUPDWLRQEDVHG on ontologies. In this chapter we propose the hierarchies to organize ontology languages and ontologies. Based on the hierarchy of ontology languages, the ontology designers need not bear in mind which ontology language the primitives exactly come from, also we can automatically DQGVHDPOHVVO\XVHWKHRQWRORJLHVGH¿QHGZLWK different ontology languages in an integrated en-vironment. Based on the hierarchy of ontologies, WKHFRQÀLFWVLQGLIIHUHQWRQWRORJLHVDUHUHVROYHG thus the semantics in different ontologies are clear without ambiguities. Also, these semantic-
FOHDURQWRORJLHVFDQEHXVHGWRHI¿FLHQWO\SURFHVV the semantic information in Semantic Web and e-business.
INTRODUCTION
The Extensible Markup Language (XML) (Bray et al., 2004) developed by the World Wide Web Consortium (W3C) has recently emerged as a new standard for data representation and exchange on the Internet. However, the information exchange based on XML is at the syntactic level (Garshol & Moore, 2004). Nowadays, how to process and exchange semantic information becomes very important. Semantic Web and e-business are two important applications which need to process the
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A Basis for the Semantic Web and E-Business
semantic information.Semantic Web (Lee, 1999) means that the Web pages are annotated with the concepts (terms and relationships) from sharing ontologies; because Web information refers to the sharing ontologies, computers can automatically understand and process the semantic information. Similarly, when different partners (agents) of e-business refer to the sharing concepts in ontolo-gies, they can semantically communicate with each other. This is a semantic e-business which is different from the traditional e-business. To process the semantic information, the traditional e-business is a person-to-person communication; now with ontologies the semantic communica-tion of e-business partners is an agent-to-agent communication.
It can be seen that ontologies play a core role in processing semantic information. Anontology GH¿QHVWKHEDVLFWHUPVDQGUHODWLRQVKLSVFRPSULV-ing the vocabulary of a topic area, as well as the rules for combining terms and relationships to GH¿QHH[WHQVLRQVWRWKHYRFDEXODU\*UXEHU +RZWRRUJDQL]HRQWRORJLHVDQGFOHDUO\GH¿QH the semantics in ontologies are very important. Presently, the ontologies are built by different organizations for their own purposes, therefore we need to effectively organize different ontologies together with hierarchies, then the concepts of WKHRQWRORJLHVFDQEHHI¿FLHQWO\XVHGWRDQQRWDWH Web pages and e-business agents, and semantic LQIRUPDWLRQFDQEHHI¿FLHQWO\SURFHVVHGEDVHG on the well-organized ontologies.
7R GH¿QH RQWRORJLHV ontology languages are required. Ontolingua (Gruber, 1992) is an ontology interchange language which was pro-posed to support the design of ontologies. Loom (MacGregor, 1991), a knowledge representation system, is used to provide deductive support. We will further introduce the XML-based ontology ODQJXDJHVLQWKH³%DFNJURXQG´VHFWLRQ
In this chapter, we propose hierarchies to effec-tively organize ontology languages and ontologies
The rest of this chapter is organized as follows. ,QWKH³%DFNJURXQG´VHFWLRQZHLQWURGXFHWKH background and the motivation of this chapter. In WKH³2QWRORJ\/DQJXDJH2UJDQL]DWLRQ´VHFWLRQ the hierarchy to organize ontology languages is proposed. We propose the hierarchy to organize RQWRORJLHVDQGGLVFXVVKRZWRUHVROYHWKHFRQÀLFWV in theRQWRORJ\KLHUDUFK\LQWKH³%XLOGLQJ2QWRO-RJ\6\VWHP´VHFWLRQ+RZWRHI¿FLHQWO\SURFHVV the semantic information in the Semantic Web DQG HEXVLQHVV LV GLVFXVVHG LQ WKH ³6HPDQWLF Information Processing in the Semantic Web and (%XVLQHVV´VHFWLRQ,QWKH³&RQFOXVLRQ´VHFWLRQ we summarize this chapter.
BACKGROUND
Some comparisons have been done to compare different ontology languages. Although XML(S) has no semantics, it may help bootstrap the de-velopment of content and tools for the Semantic Web (Gil & Ratnakar, 2002). Another comparison (Gomez-Perez & Corcho, 2002) about ontology languages is from three aspects, that is, (1) general issues (partitions and documentation), (2) attri-butes (instance attributes, class attributes, local scope, and global scope), and (3) facets (default value, type constraints, cardinality constraints, and documentation). The existing works are mainly about comparing different ontology lan-guages, then choosing the best ontology language to use. Different from the existing works, this chapter is mainly about how to organize ontol-ogy languages and ontologies with hierarchies, therefore we mainly compare the changes of primitives in different ontology languages. From WKHVHFKDQJHVZHFDQ¿QGWKHFKDQJHWUHQGVRI ontology languages, then it is motivated, that is, it is very important to effectively organize different ontology languages.
The Simple HTML Ontological Extensions
DQGGLVFXVVKRZWRHI¿FLHQWO\SURFHVVVHPDQWLF 6+2(/XNH +HÀLQH[WHQGV+70/ information in Semantic Web and e-business. with machine-readable knowledge annotated,
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A Basis for the Semantic Web and E-Business
thus the implicit semantic information can be discovered by a computer. Although SHOE has the XML version, it is not based on the Resource Description Framework (RDF) (Lassila & Swick, 2004) and RDF Schema (RDFS) (Brickley & Guha, 2004).
RDF (Lassila & Swick, 2004) is a standard ODQJXDJHRI:&IRUGH¿QLQJRQWRORJLHV5`) GH¿QHVDVLPSOHPRGHOIRUGHVFULELQJUHODWLRQ-ships among resources in terms of properties and YDOXHV$UHVRXUFHUHSUHVHQWVDQ\WKLQJVSHFL¿HG
Figure 1. The hierarchy of the RDF-based ontology languages
RDF
RDFS
DAML OIL
DAML+OIL
OWL
Table 1. Some primitives of RDF and RDFS
Cat-egory
RDF
RDFS
Primitives
rdf:ID
rdf:resource
rdf:Property
rdf:Bag rdf:Seq rdf:Alt rdfs:Class rdfs:label rdfs:comment rdfs:domain rdfs:range
rdfs:subClas-sOf rdfs:subProper-tyOf
rdfs:Container
Comment
Used to identify a class or property or any other resources Used to refer to a resource; a resource represents anything VSHFL¿HGE\D85, 7RGH¿QHDSURSHUW\WKH¿UVWOHWWHURIDSURSHUW\,`LVLQ lower case
An unordered collection (set) of members An ordered collection (set) of members
A collection (set) of alternatives of members 7RGH¿QHD&ODVVWKH¿UVWOHWWHURIDFODVV,`LVLQFDSLWDO To provide a human-readable version of a resource name To provide a human-readable description
To restrict the domain of a property To restrict the range of a property
To indicate the specialization of a class
To indicate the specialization of a property
Super class of rdf:Bag, rdf:Seq and rdf:Alt
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A Basis for the Semantic Web and E-Business
E\ D XQLIRUP UHVRXUFH LGHQWL¿HU 85, /HH Fielding, & Masinter, 1998). Properties are the attributes of resources, which have either atomic entities (strings, numbers, etc.) or other resources as their values. For a person to understand the semantics of a sentence, a sentence is organized in a subject-verb-object (SVO) form. Similarly, the fundamental design pattern of RDF is to structure data as resource-property-resource triples. Here, resource can represent both subject and object in the SVO form, while property (relationship between resources) represents the verb in the 692IRUP7KXVWKH5`)¿OHVFDQEHSURFHVVHG
semantically. An RDF model can be represented in three ways, namely, graph syntax, triple syntax, and RDF/XML syntax. In this chapter, we focus on the XML representation of RDF.
RDF organizes information in the SVO form, EXWLWGRHVQRWGH¿QHWKHPDQ\VWDQGDUGprimitives (see Table 1) required to construct ontologies. Thus, RDFS (Brickley & Guha, 2004) is created to provide some more basic primitives, such as ³VXE&ODVV2I´DQG³VXE3URSHUW\2I´WRUHSUHVHQW the relationships between classes or properties).
More semantic-rich primitives are added into the successors of RDFS, namely, U.S. Defense
Table 2. Primitive differences among DAML, OIL, DAML+OIL, and OWL
OIL DAML DAML+OIL OWL Comment
(1) Primitives included in all the four languages
Class
inverseRelation-Of
FunctionalProp-
erty
Class
inverseOf
UniquePro-
perty
Class
inverseOf
UniqueProperty
Class
inverseOf
Function-
alProperty
used to GH¿QHFODVV
if P1(x,y) then P2(y,x)
if P(x,y) and
P(x,z) then y=z
(2) Primitives not included in OIL, but included in the other three languages
s a m e C l -assAs
sameProp-
ertyAs
sameClassAs
samePropertyAs
e q u i v a -lentClass
e q u i v a -
lentProperty
C1 = C2
P1 = P2
(3) New primitives added in DAML+OIL, used by OWL
ObjectProperty
DatatypeProp-
erty
O b j e c t -Property
D a t a t y -
peProperty
relates Resource to Resource
relates Re-source to Literal
or data type
(4) OIL primitives not used by DAML+OIL, but used by OWL
SymmetricProp-
erty
Symmet-
ricProperty
if P(x, y),
then P(y, x)
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A Basis for the Semantic Web and E-Business
Advanced Research Projects (DARPA) DARPA Agent Markup Language (DAML) (Popp, 2000), Ontology Inference Layer (OIL) (Horrocks et al., 2001), DAML+OIL (Connolly et al., 2001a), and Web Ontology Language (OWL) (Harmelen et al., 2004).
DAML (Popp, 2000), which is funded by DARPA aims at developing a language to fa-cilitate the semantic concepts and relationships understood by machines. The DAML language is based on RDF and RDFS.
OIL (Horrocks et al., 2001), from the On-To-Knowledge Project, is an ontology representation language that extends RDF and RDFS with ad-ditional language primitives not yet presented in RDF and RDFS.
Now the latest extension of DAML is DAML+OIL (Connolly et al., 2001b), which has some important features of OIL imported into DAML. Presently, DAML+OIL is evolving as OWL (Harmelen et al., 2004), and OWL is being promoted as the Web ontology language of W3C. OWL is almost same as DAML+OIL, but some primitives of DAML+OIL are renamed in OWL for more easily understanding.
,QWKH³+LHUDUFK\DQG3ULPLWLYHVRI5`)DQG RDFS-Based Ontology Languages” section, we illustrate the hierarchies of the RDF-based ontol-ogy languages, and we compare the primitive differences among different ontology languages. Note that a primitive is a basic term in ontology ODQJXDJHVWKDWLVXVHGWRGH¿QHRQWRORJLHV,QWKH ³0RWLYDWLRQ´VHFWLRQZHLQWURGXFHWKHPRWLYDWLRQ of this chapter.
Hierarchy and Primitives of RDF and RDFS-Based Ontology Languages
RDF and RDFS are the ground of DAML, OIL, DAML+OIL, and OWL. In Table 1, we list some primitives of RDF and RDFS.
5`)DQG5`)6GH¿QHVRPHEDVLFSULPLWLYHV and these primitives are not capable of describing many other important concepts and relationships,
for example, equivalentClass, therefore DAML, OIL, DAML+OIL, and OWL extend RDF and RDFS by adding some new primitives. In Table 2, we compare the primitive differences among DAML, OIL, DAML+OIL, and OWL. We sum-marize the differences into several cases, and for each case, we only list a few primitives which satisfy this case. Cases: (1) primitives included in all the four languages; (2) primitives not included in OIL, but included in the other three languages; (3) new primitives added in DAML+OIL, used by OWL; and (4) OIL primitives not used by DAML+OIL, but used by OWL. The four dif-ferent cases indicate the primitive relationships among different ontology languages.
1RZZHGLVFXVVKRZWRGH¿QHDQRQWRORJ\ based on ontology languages.
Example 1. Consider a simple Person ontology VKRZQLQ)LJXUH7KHVWDUWWDJ³UGI5`)!´DW OLQHDQGWKHHQGWDJ³UGI5`)!´DWOLQH show that this ontology complies with the RDF syntax. Lines 1-4 specify some XML namespace declarations (Bray, Hollander, & Layman, 1999), WKHQZHFDQXVH³UGI´WRUHIHUWRWKHSULPLWLYHVGH-¿QHGLQWKH85/³KWWSZZZZRUJ rdf-syntax-ns#” (similarly for other namespaces). 7KHQDPHVSDFH³[VG´DWOLQHLVXVHGWRUHIHU to XML Schema in which some data types are GH¿QHG/LQHVGH¿QHDFODVV³3HUVRQ´XVLQJ WKHSULPLWLYHRI2:/³RZO&ODVV´$OVRZHFDQ VHHIURPOLQHVDQGWKDWSULPLWLYHV³ODEHO´ DQG³FRPPHQW´DUHIURP5`)6WKHUHIRUHWKHUH LVDQDPHVSDFH³UGIV´EHIRUH³ODEHO´DQG³FRP-PHQW´WKDWLV³UGIVODEHO´DQG³UGIVFRPPHQW´ /LQHVGH¿QHDGDWDW\SHSURSHUW\³RZO `DWDW\SH3URSHUW\´ ³RI¿FHBSKRQH´ VLPLODUO\ ZHFDQGH¿QHRWKHUSURSHUWLHVIRUSHUVRQIRU H[DPSOH³QDPH´DQGVRIRUWK/LQHVGH¿QH DSURSHUW\³FRQWDFWBQXPEHU´ZKLFKLVHTXLYDOHQW WRWKH³KRPHBSKRQH´
5HPDUN7KH³3HUVRQ´DWOLQHLVDQRULJLQDO GH¿QLWLRQZKLOHWKH³3HUVRQ´DWOLQHKDVDKDVK PDUN³´EHIRUHZKLFKPHDQVWKH³3HUVRQ´DWOLQH 10 is a reference. There is no namespace (URL)
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