Yu Tao
个人主页: http://link.ece.uci.edu/tyu/index.html
个人简历上介绍, 本科就读于成都电子科技大学(1995), 硕士是北邮(1998), PhD在University of California, Irvine(2002), 博士论文的题目是"QoS (Quality of Service) in Web Services: Architecture, Model and Algorithms"
她于05~07年在Web service selection with QoS constraints方面发表过一系列的论文:
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)
今天重读了一遍"Service Selection Algorithms for Web Services with End-to-end QoS Constraints (ISeBM2005)".
本文研究的是如何选择Web服务, 使得组合服务的整体QoS满足约束, 并且使效用值最大.
这篇论文对研究的问题做了一些简化:
(1) 只考虑sequantial composition model (这个是一个比较重大的简化)
(2) 只考虑具有一个QoS约束条件(delay)
使用了两种方式来解决问题: combinatorial approach, graph approach
在combinatorial approach中,
问题被建模为MCKP(多选择背包问题), 并使用了Exhausive search, dynamic programming, Pisinger这3种算法来求解.
这种方式的缺陷是无法对transmision delay和cost进行建模. 由于同一个service class内的不同service可以由不同的provider提供, 而不同的provider可以处于不同的网络, 因此service之间的transmission delay/cost是存在差异的, 但是在combinatorial approach中只能假定两个service之间的transmission delay/cost是一样的.
在graph approach中,
使用DAG进行建模(如果还有其他composition model ,比如parallel, 似乎很难用文中现有的建模方法), 经过转换, 将cost/benefit等参数映射到边上.
将问题建模成图论中的constrained shortest path问题.
使用了Constrained Bellman-Ford(CBF)和Constrained Shortest Path(CSP)算法来求解.
CBF算法是指数级的
其他注意点
(1) dominate relationship (S5.2.3, 算法1中提到)
两条路径a, b, 如果(a.utility >= b.utility) && (a.delay <= b.delay ), 则称路径a dominate 路径b, 即路径a在每一个方面都优于路径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.