| Summary: | 碩士 === 國立臺灣大學 === 資訊管理學研究所 === 94 === As the number and variety of Web Services continue to grow, we will soon be able
to compose several Web Services as a more sophisticated service that meets a particular
user’s needs. However, how to achieve this automatically poses great challenges. The
difficulty of automatic Web Services composition can mainly be attributed to the lack of
semantic interoperability in current Web Services technologies. Consequently, there have
been many ongoing efforts in applying Semantic Web technologies to Web Services.
In this thesis, we attempt to investigate and improve a semantic-based approach to
providing customized services by dynamically assembling existentWeb Services. We focus
on the problem of combing Web Services that may be invoked independently without a
particular order; this is to be contrasted with the usual kind of service composition where
the data/control flow from one service to another is essential. In the semantic approach to
service combination, the description of a Web service is envisioned to consist of two parts:
one is the service interface described by WSDL, which contains the necessary information
for invoking the service and the other is the service profile expressed using Web Ontology
Language (OWL) based on Description Logics, which contains sematic information that
characterizes the service, such as information of the service provider. From the service
provider’s perspective, the service profile can be seen as the service advertisements. The
service requestor describes his needs by postulating a service profile, referred to as the
service requirement, which after decomposition (if necessary) is to be matched against
available service advertisements. With service requirements and service advertisements
described according to the same set of ontologies, the suitable services can be matched
and combined automatically.
One main improvement to the aforementioned semantic approach is an innovative
method to complete service requirements. Through examining concept definition f the
requirement, we will know the incomplete information and trigger events to ask the customer
to complete the requirement. Besides, we adopt the Jess rule engine and the Racer
DL reasoner to perform constraint checking to ensure the consistency of the knowledge
base. In the ontology modeling aspect, although OWL includes a rich set of class constructs,
it is very weak in what can be said about properties. We use SWRL (Semantic
Web Rule Language) to complement the expressive power, particularly the role composition
construct.
To validate our approach, we design and implement a prototype service combination
system for the tourism domain, called the Traveller, as a plugin application in the wellused
Prot´eg´e system. The system aims to help a customer or a travel agent to discover,
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combine, and invoke the desired Web services for a trip. The customer can give the system
his incomplete or even ambiguous trip requests. The system will check the request’s
consistency, and help the customer complete his requirements. It then returns exactly or
approximately matched services according to the customer’s requirements. Finally, the
customer can make a decision to actually invoke the matched Web Services.
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