Tao Yu的論文之一 “Service Selection Algorithms for Web Services with End-to-end QoS Constraints (IS

Yu Tao
個人首頁: http://link.ece.uci.edu/tyu/index.html
個人簡曆上介紹, 本科就讀於成都電子科技大學(1995), 碩士是北郵(1998), PhD在University of California, Irvine(2002), 博士論文的題目是"QoS (Quality of Service) in Web Services: Architecture, Model and Algorithms"

她於05~07年在Web service selection with QoS constraints方面發表過一系列的論文:
T. Yu and K.J. Lin "Service Selection Algorithms for Web Services with End-to-end QoS Constraints", Journal of Information Systems and e-Business Management, Volume 3, Number 2, July 2005
T. Yu and K.J. Lin, "Service Selection Algorithms for Composing Complex Services with Multiple QoS Constraints", ICSOC2005
T. Yu and K.J. Lin, "Adaptive algorithms for Finding Replacement Services in Autonomic Distributed Business Processes." ISADS2005
T. Yu and K.J. Lin "A Broker-Based Framework for QoS-Aware Web Service Composition", EEE05
Tao Yu, Yue Zhang, Kwei-Jay Lin: Efficient algorithms for Web services selection with end-to-end QoS constraints. TWEB 1(1): (2007)

今天重讀了一遍"Service Selection Algorithms for Web Services with End-to-end QoS Constraints (ISeBM2005)".
本文研究的是如何選擇Web服務, 使得組合服務的整體QoS滿足約束, 並且使效用值最大.
這篇論文對研究的問題做了一些簡化:
(1) 只考慮sequantial composition model (這個是一個比較重大的簡化)
(2) 只考慮具有一個QoS約束條件(delay)

使用了兩種方式來解決問題: combinatorial approach, graph approach
在combinatorial approach中,
問題被建模為MCKP(多選擇背包問題), 並使用了Exhausive search, dynamic programming, Pisinger這3種演算法來求解.
這種方式的缺陷是無法對transmision delay和cost進行建模. 由於同一個service class內的不同service可以由不同的provider提供, 而不同的provider可以處於不同的網路, 因此service之間的transmission delay/cost是存在差異的, 但是在combinatorial approach中只能假定兩個service之間的transmission delay/cost是一樣的.

在graph approach中,
使用DAG進行建模(如果還有其他composition model ,比如parallel, 似乎很難用文中現有的建模方法), 經過轉換, 將cost/benefit等參數映射到邊上.
將問題建模成圖論中的constrained shortest path問題.
使用了Constrained Bellman-Ford(CBF)和Constrained Shortest Path(CSP)演算法來求解.
CBF演算法是指數級的

其他注意點
(1) dominate relationship (S5.2.3, 演算法1中提到)
兩條路徑a, b, 如果(a.utility >= b.utility) && (a.delay <= b.delay ), 則稱路徑a dominate 路徑b, 即路徑a在每一個方面都優於路徑b.
(2) topological order
Definition: A numbering of the vertices of a directed acyclic graph such that every edge from a vertex numbered i to a vertex numbered j satisfies i<j.