單一的網路服務(Web Service)僅能達成有限的功能，網路服務組合(Web Service Composition)的概念即在於藉由將網路上不同的服務元件加以組合利用，則能夠計算、處理並解決更加複雜的問題與任務，創造更完整或創新的新型態企業流程，進而發揮更大的效益與競爭優勢。然而一個服務組合需求者如何針對其特定的服務需求，正確分析其達成執行目標所需的流程架構，進而依照此一流程分析結果，快速而效率地找出符合完成特定流程目標之相關網路服務，並加以正確組合及有效率地執行，同時又能確保網路服務組合結果的正確與品質，是網路服務組合中的一個重要的研究議題。
在網路服務組合過程中選擇適合的網路服務元件時會考慮到所謂功能性與非功能性的需求，前者是完成特定服務目標在功能層面上所需具備的基本條件，而後者則是涉及整個服務組合執行時在執行效率、安全性與其他品質屬性上的要求。本研究即是基於上述的構想下，提出一個能同時兼顧功能與品質需求下，整合工作流程分析與運用知識本體進行QoWS(Quality of Web Service)評估的二階段網路服務組合模式。第一階段透過工作流程的分析，以標準化的規格描述每個子流程功能層次的需求參數，並以此作為候選網路服務查詢的基礎；而在第二階段則根據各項子流程的品質層次需求描述，進一步針對候選網路服務進行品質需求評選，並透過標準化的程序計算其品質分數，藉以取得最佳化的網路服務組合結果。而透過此一模式的建構與應用，期盼對於未來網路服務組合的發展能夠加入更完善與結構化的思維。

A single web service is only able to provide limited functions. The concept of web service composition, however, is able to compute and solve much more complicated problems and tasks, and furthermore helps to create more complete and innovative enterprise process by aggregating and combining web service components, which brings more effectiveness and competitive advantage. On the other hand, one of the key research issues of web service composition is how to analyze the workflow correctly to fullfil specific web service composition requirements in compliance with the task to be executed. Then, according to the result of workflow analysis, finding out the related web service components efficiently and further composing them correctly and within the service quality requirements are essential to web service composition.
To select suitable web service components, there are two main concerns to be taken into consideration, which are so called functional and non-functional requirements. The functional requirements are the basic to get correct results of composit service execution, while non-functional requirements focus on the quality of execution, such as performance, accuracy, security and so on. The main object in our research is to propose a two-phase web service composition model applying workflow analysis and service quality evaluation technology based on QoWS ontology, which conforms to both the functional and non-funational requirements metioned above. In phase one, the output of workflow analyzing is recorded with uniform description of functional requirements for each sub-process and the list of candidate web services is also queried according to the description at the same time. In phase two, we use the quality requirements description to evaluate each candidate web service and get the optimizing composition result according to a normalized score. With this model to be constructed and applied, we believe that the development of web service composition in the future will be more complete and more structured.

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