Journal of Computational Information Systems5:6(2009) 1669-1677 Available at http://www.JofCI.org
Toward Multi-ontology Based Interoperability in Web Service Registry Cheng ZENG1,2, Keqing HE1,† , Bing LI1, Chong WANG1, Yangfan HE1 1
State Key Laboratory of Software Engineering, Wuhan University, Wuhan 430072, P.R. China
2
Faculty of Mathematics and Computer Science, Hubei University, Wuhan 430062, P.R. China
Abstract Semantic interoperability is an important issue in web service registry (WSR). This paper presents an innovative approach to solve deep interoperability of multi-ontology in the same Domain, which will lead to the interoperability of web service based on these ontologies. We solve the issue by using ISO SC32 19763-3:MFI4OR Metamodel Framework for Interoperability: Metamodel for Ontology Registration) to register the different ontologies and the evolution information between them in the same domain for annotation to web service. Finally a domain-oriented prototype system of web service annotation for supporting multi-ontology interoperability is designed and evaluated. Keywords: Semantic Interoperability; Web Service Registry; Reference Ontology; Local Ontology
1. Introduction Web services are the latest attempt to revolutionize large scale distributed computing. Service oriented architectures (SOA) will provide the basis of the next generation of distributed software systems. With the growing popularity of Web services, there arise issues of finding relevant services, especially with the possibility of the existence of thousands of Web services. Therefore, how service providers publish service description information and how service consumers discover appropriate services dynamically turn to be an important problem in SOA. Service registry acts as an information mediation role in the triangular SOA to solve that problem, which is responsible for such burdens that enable service providers to publish their service more effectively and service consumers to find service information needed more accurately and easily. WSDL [1] is a type of syntactic description. However, service discovery need to know the business meaning of service interface parameters such as Input, Output or Operation. Domain Ontology (DO) is used to add semantic information to tackle this problem [2]. The discovery, in particular, is enriched with the adoption of semantic-aware analysis to improve the responsiveness of the registry and help users with solutions (services) that are close enough to what they would have liked to get (even if they do not fully match their expectations). As we all know, DO is always constructed and standardized by Domain Experts which use common approved concepts and relationship among them, but sometimes service providers
†
Corresponding author. Email addresses:
[email protected] (Keqing HE).
1553-9105/ Copyright © 2009 Binary Information Press December, 2009
1670
C. Zeng et al. /Journal of Computational Information Systems 5:6(2009) 1669-1677
maybe use some concepts outside of DO to annotate. For meet their requirement, it is necessary to define their own ontology to annotate web service. Therefore how to define their own ontology and how to keep the relationship between the ontology defined by service providers and the ontology defined by domain experts become the important issue which will lead to the interoperability among the DOs in the same domain. In this paper, motivated by the above stated requirement, the new approach of web service annotation for supporting semantic interoperability in WSR is presented by means of ISO SC32 19763-3: MFI4OR (Metamodel Framework for Interoperability: Metamodel for Ontology Registration) [3]. Based on the approach, the main contributions in this paper are as follows: 1） We create and register the different forms of Domain Ontology (multi-ontology) in order to annotate web service., including Domain Reference Ontology (DRO) and Domain Local Ontology (DLO) evolved from DRO, 2） The management platform of Domain Ontology is designed for semantic interoperability. In this platform, DRO, DLO and the evolution information between them are all registered and recorded in order to improve the interoperability in WSR. The remainder of the paper is organized as follows. Section 2 gives an overview of the theoretical foundation of MFI4OR. Section 3 presents how to realize semantic interoperability in web service annotation. Section 4 gives the evaluation of the prototype system for semantic interoperability. The related work is discussed in Section 5, followed by the conclusion and future work in Section 6. 2. Theoretical Foundation of Interoperability 2.1. What is MFI4OR In order to enhance the degree of interoperability in Web Service Registries, we exploit ISO SC32 19763: MFI, which provides a framework for metadata registration by integrating metadata registration standards at the metamodel level. Now MFI is composed of 7 parts, namely, the Reference Model of MFI, the Core Model of MFI, MFI for Ontology Registry (MFI4OR), MFI for Mapping, MFI for Process Model Registration, MFI for Registry on Registries and MFI for On demand Selection of Model. MFI Core Model specifies a basic framework for metamodel and model registration. The other parts in MFI inherit some metaclasses from MFI Core Model. And some new metaclasses will be added to meet the special registration requirements of different kinds of models. In this paper, our solution for semantic interoperability is mainly based on MFI4OR.
Ontology provides a basic technology to support the interoperability of different systems over a distributed and heterogeneous environment. The interoperability of different systems is based on same ontology or different ontologies. If the systems commit to the same ontology, one system can use it to describe their requests and responses, while other systems committing to the same ontology can understand such requests, so the interoperability of them can be easily realized. But most cases are the latter one when we use different ontology to annotate web service in WSR. So it is necessary to solve these two levels of interoperability for web service. MFI4OR is mainly used for providing a common metamodel framework for ontology registration so that ontology definition from every metamodel could be unified [3, 4]. As shown in Figure 1,
C. Zeng et al. /Journal of Computational Information Systems 5:6(2009) 1669-1677 1671
MFI4OR provides the solutions by defining “Reference Ontology” (RO), “Local Ontology” (LO). Both RO and LO are composed of the Ontology Component (OC: ROC or LOC), and Ontology Component is composed of the Ontology Atomic Construct (OAC: ROAC or LOAC). Figure 1 shows the ROC or ROAC defined in RO can be reused by the other ontologies, while that defined by LO can only for its own definition purpose. RO is used to represent common ontology in some domains, which is created and maintained by experienced domain experts. So RO is comparatively stable in that domain it belongs to. Different from RO, LO is often evolved from RO for particular application system. The LOs evolved from the same RO can interoperate with each other, which provide a solid foundation for semantic interoperability in Web Service Registries. Besides RO and LO, the evolution information from RO to LO is a core part in MFI4OR. Next section will discuss the details of ontology evolution rules.
Fig.1 Basic Model of MFI4OR
2.2. Ontology Evolution Rules The ontology evolution rules can help record the detailed changes when LOs evolve from RO, which ensure that the difference of ontologies will not hamper the interoperability between RO and LOs. There always exist three basic operations: equivalence operation, enhancement (or add) operation and contraction (or delete) operation. Theoretically, the three basic operations can cover all the possible modifications on RO and LO because any complex evolution can be decomposed, viewed as a sequence consisting of these three operations and driven by the following rules: (1) SameAs Rule. It can set up the equivalent mapping between instances of Ontology, Ontology Component or Ontology Atomic Construct. If the semantic conflict occurs, we need to inform the changes to the petitioner for a better understanding of the actual needs. When SameAs Rule is adopted, there is no change in connotation of corresponding concept. (2) Enhancement Rule. It is special for adding some new elements to the original ontology when versioning and evolving. If there exists the relationship of ObjectProperty or SuperClass/ SubClass between the newly added element and the original element, we will add the new element to the LO. When Enhancement Rule is adopted, it may lead to semantic inconsistency. To maintain semantic consistency, the newly added artifact should have a unique name and be consistent with the content and context of the original domain.
1672
C. Zeng et al. /Journal of Computational Information Systems 5:6(2009) 1669-1677
(3) Contraction Rule. It is often adopted in ontology evolution management to delete concepts，attributes, properties, constraints and so on. When Contraction Rule is executed, the cascading effects will be considered. For example, when deleting a class, the relationship corresponding to this class may be deleted. Therefore the delete operation should be carefully adopted because it may destroy the integrity of real registry model. In order that the LOs evolved from the same RO can understand each other to realize the interoperability, the evolution information should be recorded when evolution rules are adopted. In this paper, the evolution information is kept as the form shown in Table 1 according to MFI4OR. This information shows that the concept XXX in LO is same as YYY in RO. That is to say, according to the SameAs Rule, XXX in LO can understand YYY in RO which will realize the interoperability between XXX and YYY. Table 1 Evolution Information from RO to LO Local Ontology Component attribute of LO
Value
Name
XXX
URI
URI_ XXX
modelType
OWL
beforeChange
YYY :
the Concept in Reference Ontology
afterChange
XXX:
the Concept in Local Ontology
evolutionRule
SameAs Rule
consistentChange
True
Obviously, ontology modification is decomposable into a sequence of three basic rules above, and the evolution information of given ontology should also correspond to a set of evolution information items. Now the first version of MFI4OR has become the international standard since 2008. This version only includes the SameAs Rule at present (See Figure.1), and Enhancement Rule and Contraction Rule will be included in the second version of MFI4OR in the future. Therefore the evolution rules from RO to LO described in following parts of the paper focus on the SameAs Rule. This section shows the theoretical foundation of interoperability. Firstly MFI4OR is briefly introduced. Then we focus on the evolution rules which ensure the interoperability between LO and RO. Section 3 will illustrate how to use the theoretical foundation to realize semantic interoperability in WSRs. 3. Multi-Ontology Based Interoperability in Web Service Registry 3.1. Implementation Mechanism As we all know, Domain Ontology (DO) is always constructed and standardized by Domain Experts which use common approved concepts and relationship among them, but sometimes publisher maybe use some concepts outside of DO. It is necessary to define their own concepts, which can be used to annotate web service, to meet their requirements. We regard the DO defined by experts as Domain Reference Ontology (DRO) and the DO defined by users as Domain Local Ontology (DLO). Figure 2 shows DRO and DLO can both be adopted to add semantic information to Web Service. That is to say, we extend the scope of
C. Zeng et al. /Journal of Computational Information Systems 5:6(2009) 1669-1677 1673 semantic annotation in Domain, which will enhance the flexibility during the process of service publication and discovery. Evolve
Fig.2 Multi-ontology Annotation based on MFI4OR
However, DRO and DLO are not isolated but interrelated to each other. Based on MFI4OR, the evolution information between DRO and DLO should be registered and recorded, which will improve the interoperability between them in WSR. As mentioned in section 2, although there exist three evolution rules between DRO and DLO, we are ready to adopt SameAs rule because this rule is the part of the first version of MFI4OR which has already become International Standard. Figure 3 shows the user interface of annotation with DRO or DLO. Once service provider selects Service Domain, such as logistics or transport, DRO and DLO will be imported to this platform for the use of annotation to web service. The evolution information between DRO and DLO will lead to the interoperability between them. Person
Person
Businessman
Businessman
Consumer
Seller
subClassOf Fig.3 UI of Annotation with DRO or DLO
(a) DRO
Buyer
Seller
subClassOf
(b) DLO
Fig.4 Fragment of DRO and DLO
For example, there is a fragment of DRO shown in Figure 4(a). When evolving from DRO to DLO, Service Providers can reuse the concepts of person, businessman and seller which maybe an Ontology Component or Ontology Atomic Construct in DRO, and more important can define the new concept of Buyer for their requirement shown in Figure 4(b). Meanwhile we adopt SameAs rule to record the evolution
1674
C. Zeng et al. /Journal of Computational Information Systems 5:6(2009) 1669-1677
information between consumer in DRO and buyer in DLO shown in table 2. It shows that DLO is not separated from DRO but evolved from DRO through the evolution information. If DLO is adopted to annotate web service, when querying the web service whose output is buyer, the returned candidate list of web service will include the web service whose output is consumer according to evolution information between the DRO and DLO besides the web services whose output is businessman or person according to traditional semantic query. That is to say, interoperability between DRO and DLO in the same Domain is realized. Table 2 Evolution Information of DLO Evolution information attribute of LO
Value
Name
Buyer
URI
URI_ buyer
modelType
OWL
beforeChange
Consumer
afterChange
Buyer
transformationRule
SameAs Rule
consistentChange
True
3.2. Management of Multi-ontology In order to effectively manage the DRO, DLO and the evolution information between them, we design the Platform of Ontology Registry and Repository (PORR). In PORR, whatever DRO or DLO, they are both registered by the ontology constructing pattern “Ontology – Ontology Component – Ontology Atomic Construct” defined in MFI4OR shown in Figure 5.
Fig.5 DRO/DLO Registration
Figure 6 illustrates how to define the SameAs relationship between DRO and DLO. In the left pane (Reference Ontology), when you choose the ontology in the dropdown list RO, the Ontology Component in RO will be list in the ListBox. And then when an Ontology Component is selected, the Ontology Atomic Construct will also be list. In the right pane (Local Ontology), there exist the same operations as the left pane. After doing that we can define the SameAs relationship between the Ontology Component and Ontology Atomic Construct in DRO and that in DLO. According to these SameAs relationship between the DRO and DLO, the semantic interoperability in web service registry can be achieved.
C. Zeng et al. /Journal of Computational Information Systems 5:6(2009) 1669-1677 1675
Ontology
Ontology Atomic
Fig.6 SameAs Relationship Definition between DRO/DLO
4. Evaluation To evaluate our approach, we take precision, the number of returned candidate web services and the average number of web services as the evaluation metrics. We make the experiments in WSR which registers about 100/200/300 services at a workstation of 1GB RAM, 2.6GHz CPU with Microsoft Windows XP. The result shows that the number of the returned candidate services annotated with DRO/DLO is increased by 40% compared to the number of the returned services annotated with DO. In the experiments evaluated above, the ratio of recall has been increased greatly. In the following experiment we will take precision into account. In this evaluation, we execute 40 simulation experiments to compare annotation with DO and DRO/DLO. The ratio of precision is increased nearly 20% shown in Figure 8 because our proposal not only makes full use of the logic reasoning algorithm in single ontology just as the traditional methods has done for many years, but also focus on the interoperability among multi-ontology based on MFI4OR to achieve the high performance.
Fig.7 the relationship of the number of candidate web service and the number of web service in WSR
Fig.8 Comparison of the Precision Ratio
1676
C. Zeng et al. /Journal of Computational Information Systems 5:6(2009) 1669-1677
5. Related Work
Our work presents an approach for adding semantics to Web services based on MFI4OR. In fact, much work has been done on semantic annotation to Web services. We discuss two representatives of them. A classification method is described in [5]. It uses machine learning algorithms to help users simplify the search for relevant ontology. Unfortunately, the method considers just names of WSDL concepts, ignoring the structure of them. Moreover, it uses vocabularies, but does not use ontology which is more descriptive and capture domain more accurately for classification. MWSAF [6] uses a media structure called SchemaGraph to facilitate the matching between XML schema and ontology to find the relevant ontology. However, since the matching results are not good if WSDL files do not have good structure or the ontology becomes much comprehensive, it is also not suitable for our context. Moreover, a template-based markup tool is proposed in [7], which can improve annotation accuracy significantly. But as used for semantic web content annotation, the template is over complex, and has a poor reusability considering the various web contents. The common factor in these approaches is only relating signatures of Web service to SINGLE domain ontology, but our approach can use multi-ontology in the same domain, which are not isolated but interrelated to each other based on ontology evolution rules defined in MFI4OR, to annotate web service, which will extend the scope of semantic annotation in the Domain and greatly enhance the flexibility during the process of service publication and discovery. 6. Conclusions and Future Work In this paper, we focus on the issue of semantic interoperability in web service annotation. Based on MFI4OR, the interoperability between the DRO and DLO in the same Domain will help to solve the issue. In WSR, Service Provider can use DLO defined by himself to annotate Web service, which will interoperate with DRO defined by domain experts. We also establish Ontology Evolution Rules which provide some verifying criterions to ensure the semantic consistency between the original and the new ontology. Meanwhile the Platform of Ontology Registry and Repository (PORR) is designed to effectively manage the DRO, DLO and the evolution information between them. The evaluation result illustrates that the performance is increased greatly by use of our approach. In future, we plan to expand the Ontology Evolution Rules which make the evolution information to be recorded comprehensively and clearly, and verification criterions should be attached to each kind of rules to avoid semantic contradiction when ontology evolving. Acknowledgement This work is supported by National Basic Research Program (973) of China under grant No. 2007CB310801, National High Technology Research and Development Program (863) of China under grant No. 2006AA04Z156, National Natural Science Foundation of China under grant No. 60873083,60803025, 60970017 and 60903034, Natural Science Foundation of Hubei Province for Distinguished Young Scholars under grant No. 2008CDB351, Natural Science foundation of Hubei Province under grant No. 2008ABA379, Research Fund for the Doctoral Program of Higher Education of China under grant No. 20070486065 and 20090141120022, China Postdoctoral Science Foundation under grant No. 20090460107, and the Research Project funded by Wuhan University under grant No. 6082005 and 6082007, Scientific and Technological research projects of Hubei Province Education Department under Grant No.D20091012.
C. Zeng et al. /Journal of Computational Information Systems 5:6(2009) 1669-1677 1677 References [1]
R. Chinnici, J. Moreau, A. Ryman, and S. Weerawarana, Eds., “Web Services Description Language (WSDL) Version 2.0 Part 1: Core Language”, W3C Candidate Recommendation 27 March 2006; http://www.w3.org/TR/2006/CRwsdl2020060327
[2]
K. Verma and A Sheth, “Semantically Annotating a Web Service,” IEEE Internet Computing 11 (2),March–April 2007, pp. 83–85
[3]
ISO/IEC 19763-3:2007. Keqing He. http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm? csnumber=38637, 2008
[4]
Chong Wang, Keqing He, Yangfan He. MFI4Onto: Towards Ontology Registration on the Semantic Web [A]. In Proceedings of 6th International Conference on Computer and Information Technology, CIT 2006, Seoul, 2006, pp.40-46
[5]
A. Hess and N. Kushmerick. Automatically attaching semantic metadata to Web services. Proceedings of the 2nd International Semantic Web Conference, ISWC 2003
[6]
Patil A, Oundhakar S, Sheth A, Verma K. METEOR-S Web service annotation framework. In Proceedings of the 13th Int'l World Wide WebConference, New York, ACM Press, 2004, pp.553-562
[7]
Brian Kettler, James Starz. A Template-Based Markup Tool for Semantic Web Content. Proceedings of ISWC2005, LNCS 3729, 2005, pp. 446-460
