旅行者─一個運用語意網技術的服務組合系統

Abstract

網路服務技術提供了一個分散式系統發展的架構，網路服務可以加以組裝形成一個完整的整合性服務，以滿足特定使用者的需求。然而如何自動的組裝網路服務形成一個客製化的服務組合將會是一項極具挑戰的任務。針對這項挑戰，我們提出了一個網路服務組合的方法，這個方法主要是運用語意網的知識本體和相關的自動推理技術來達成網路服務的搜尋、組合、和執行。 根據這個方法，我們應用在旅遊服務的組合，開發了一個旅行者的雛型系統，它是建構於Protégé知識庫系統上的應用程式，而其中知識庫中的知識本體主要由OWL本體論語言加以定義，而知識庫中的規則是由SWRL規則語言所加以描述。

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, ii 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.