網路服務架構下之最佳化流程組合的選擇方法

A Selection Approach for Optimized Web Services Compositions

網路服務技術（Web services）利用XML-Messaging傳遞方式，簡化了異質系統間的整合，而服務導向架構更將需求及提供的關係，利用仲介機制予以透明化，因此大幅增加了系統整合的彈性。經由公用仲介者的查詢，需求者可獲得許多功能性相同的服務，而若商業模式需要服務間的串聯協同時，候選的服務組合將會很多，因此如合篩選服務的組合將是重要課題。本研究是以常用的服務品質項目（例如價格、執行時間、可靠度等）為依據，並修正多準則決策中的ELECTRE方法為我們的評估模型，此修正模型克服了傳統方法門檻值過高以致無法獲得比較關係的缺點，因而可在眾多的候選方案中，以優劣順序排列，並挑選出最佳的組合方案。本研究最後以一簡單的例子，介紹修正模型的使用及其改善篩選服務組合的成效。

Web services technology utilizes the XML-messaging to implement discovery, registry, and binding within the Web. It facilitates the integration problem among heterogeneous systems. The Services Oriented Architecture (SOA) establishes a services broker mechanism to intermediate services between requesters and providers. Since the broker mechanism reduces the complexity in naming of distributed computing, it raises the amount of selectable candidates. Moreover, in most e-commerce circumstances, there are a lot of choices of Web services compositions when collaboration is required. Therefore, to select an optimal Web services composition is an essential. This paper utilizes a modified ELECTRE model to evaluate quality items within Web services compositions. The original ELECTRE is an approach in the Multiple Attribute Decision Making (MADM) area. Because its threshold values of criteria are strict, the positive outcomes may not obviously. On the other hand, the qualified Web services are filtered before a composting process. It is a different scenario, since the selectable Web services compositions are all potential candidates. Therefore, we adjust threshold values to commit these particular circumstances. We also utilize some common quality items as the input factors of the model. Finally, we present a case study to demonstrate the utilizations of the modified ELECTRE model. The results are positive.