一個基於服務品質的Web服務選擇演算法

Abstract

Web services透過標準界面的制定，提供了應用程式整合的良好解決方案。其中，基於服務品質的服務組合就是一個廣泛被使用用來結合多個Web services以建立新的應用程式的一項方法，它提供一個彈性的方式，將複雜的應用程式透過抽象流程來描述，並呼叫所選擇的Web services來執行抽象流程，使用者能針對抽象流程設定QoS限制，透過一個服務挑選機制的執行，協助使用者挑選出滿足功能需求以及QoS限制的一組服務。然而，此方法存在一個缺陷，當使用者設定嚴苛的QoS限制時，服務挑選的可行解可能找不到，在此一情況下，服務組合也因此而失敗。 在這個研究中，我們首先提出一個基於服務品質的服務組合框架，並且介紹一個快速服務組合機制，此機制提供使用者一個較為效率且方便的方式來產生所需的應用程式，毋須執行服務挑選演算法。接下來，介紹一個可釋放的基於服務品質的服務挑選演算法，它是一個啟發式的演算法，當在服務挑選中找不到可行解時，此演算法會釋放一部分的服務品質限制，來找出一個建議解提供給使用者，在執行服務挑選之前，使用者可依據其需求設定可釋放的服務品質限制。

Web services define standard interfaces those provide good solutions for application integration. Quality of Service (QoS) -based web service composition (QWSC) is a methodology used widely to build new application by combining multiple web services in a flexible way. A complex application can be described as an abstract process that can be executed by invoking a number of selected web services. Users can specify the QoS constraints for the abstract process and then a service selection is performed to identify a set of available web services that fulfill not only the functionality but also the QoS constraints. However, there is a drawback for QWSC. If the user introduces severe QoS constraints for an abstract process, no feasible solution for the services selection can be identified and the service composition fails In this research, we first propose a framework for QWSC and introduce a quick service composition mechanism. The quick service composition provides users an efficient and convenient way for creating the required application without performing the service selection algorithm. Then we introduce a relaxable QoS-based service selection (RQSS) which is a heuristic algorithm of service selection for QWSC. If no feasible solution for service selection can be identified, RQSS can find a recommended solution by relaxing some of the QoS constraints. Users can specify which QoS constraints are relaxable on their own before the service selection.