服務導向架構提供網路服務組合一個彈性的框架。一個網路服務組合可以由工作流程來表示，並且對於工作流程當中的每一個任務，一些提供相同功能的候選服務是可用的。
在先前的研究當中(Hwang, Hsu, & Lee, 2014)，基於模擬組成元件服務的服務質量機率分佈提出一個網路服務選擇架構。先前的方法在拆解服務品質限制的階段使用了每一個候選服務平均QoS值。然而，候選服務之間異質性的偏差可能會導致不正確的任務服務質量預測。
我們提出一個方法考慮到服務質量機率分佈的標準差並且選出一組初始挑選服務。服務挑選的目的是獲得最大化的global QoS conformance。基於服務質量機率分佈，實驗結果顯示我們提出的方法改善了先前方法在服務挑選的表現。

Service-Oriented Architecture (SOA) provides a flexible framework for service composition. A composite web service is represented by a workflow, and for each task within the workflow, several candidate Web services which offer the same functionality may be available. In previous work (Hwang, Hsu, & Lee, 2014), Hwang et al. propose a service selection framework based on probabilistic QoS distributions of component services. Their method decomposes a global QoS constraint into a number of local constraints using the average QoS value of each candidate service. However, heterogeneous deviation among candidate services may lead to the suboptimal selection. We propose an initial service assignment finding method with considering the standard deviation of QoS distributions. The objective of service selection is to maximize the global QoS conformance. Experimental results show that the proposed approach significantly improves the performance in probabilistic QoS-based service selection method, in terms of both global QoS conformance and running time.

CHAPTER 1-Introduction 1
1.1 Background 1
1.2 Motivation 2
CHAPTER 2- Literature Review 4
2.1 Modeling Service QoS 4
2.2 Local Selection vs. Global Optimization 5
2.3 Web service selection 7
CHAPTER 3 - Problem Definition 10
3.1 Preliminaries 10
3.2 Problem description 12
CHAPTER 4 - Our Approach 18
4.1 Architecture of our Approach 18
4.2Decomposition of Global Constraint 22
4.3 Identification of locally optimal services 24
4.4 Computation of Global QoS Conformance for a Web service Assignment 25
4.5 Adjustment of Web service Assignment 25
CHAPTER 5 - Performance Evaluation 26
5.1 Experiment Design 26
5.1.1 A scenario 26
5.1.2 Experimental Data Generation 29
5.1.3 Evaluation Method 32
5.2 Experimental Result 33
CHAPTER 6 - Conclusion 42
References 43

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