[论文泛读] Reliability of Web Service Composition两篇
[泛读1] Reliability Prediction and Sensitivity Analysis of Web Services Composition (2008)
Duhang Zhong, Zhichang Qi and Xishan Xu. Reliability Prediction and Sensitivity Analysis of Web Services Composition. Petri Net,Theory and Applications, Book edited by: Vedran Kordic, ISBN 978-3-902613-12-7, pp. 534, February 2008, I-Tech Education and Publishing, Vienna, Austria
使用Stochastic Petri Nets(SPNs)对Web服务组合进行建模(基于工作流结构, 如顺序, 并发等). 服务用库所(place)来表示, 不同的迁移(transition)代表服务执行是否成功, 每个迁移以一定的概率(这个概率跟该服务的reliability有关)被触发(fired). 这样组合服务可以用一副Petri Net表示出来(文中称为CSPN, Composite Service Process Net model). 使用相关工具(比如snpn), 就可以计算出这个组合服务的reliability.
作者钟读杭单位是国防科技大学, 他之前有一篇lncs的论文(Duhang Zhong, Zhichang Qi: A Petri Net Based Approach for Reliability Prediction of Web Services. OTM Workshops (1) 2006: 116-125)讨论相同问题的, 本文新加了sensitivity analysis这部分, 讨论了成员服务的reliability变化和usage profile变化对组合服务reliability的影响.
[泛读2] Measuring Reliability of Applications Composed of Web Services (HICSS, 2007)
Time: 1.5 hours
Hangjung Zo, Derek L. Nazareth, Hemant K. Jain, "Measuring Reliability of Applications Composed of Web Services," hicss, pp.278c, 40th Annual Hawaii International Conference on System Sciences (HICSS'07), 2007
这个夏威夷的会议已经开了40多届了, unrank, 看起来是个旅游会议(50%左右的接收率) , 今年的截稿日期已经过了(June 15).
这篇论文有10页, 不过看下来觉得实质内容很少. 主要是在讨论组合服务的reliability计算, 使用了遗传算法进行服务选择. 以下是论文笔记:
1. 作者对Midwest地区的IT architects进行调查, 关于选择Web Service时何种QoS属性最被看重. 如图, Reliability最重要.
2. 关于reliability的定义
对于software reliability:
"the probability that the software will be functioning without failures under a given environmental condition during a specified period of time"
----Xie, M., Software Reliability Modelling, World Scientific Publishing Co., Singapore, 1991.
"a percentage of failure cases in a given number of attempts to compensate for variations in usage over time"
----A.L. Goel, "Software Reliability Models: Assumptions, Limitation, and Applicability," IEEE Transactions on Software Engineering, Vol. SE-11(12), December 1985, pp. 1411-1423.
----Musa, J. D., Software Reliability Engineering, McGraw-Hill, New York, NY, 1999.
本文对web service reliability的看法:
"… as a measure of failure-free operation, without modeling the source and type of failure."
"... it is more natural to measure reliability as a percentage of failures rather than a probability that the failure will occur during a fixed time frame."
3. (S2.2) 本文采用了Cardoso提出的reliability的聚合方法(基于工作流). 并假设服务之间的reliability是互相独立的.
4. 对这篇论文有2个疑问
(1) (S3)中提到要"decompose business process into sub-processes", 但是后来并没有将如何decompose, 只在(S5)中举了一个已经decompose好的例子.
(2) 本文只考虑服务组合的一个QoS属性(即reliability), 如果只考虑一个QoS属性的话, 那么针对每个task的最优解就能构成组合服务的全局最优解, 那还有必要用遗传算法来求近似解吗?
