[論文泛讀] Reliability of Web Service Composition兩篇

文章目錄

• [泛讀1] Reliability Prediction and Sensitivity Analysis of Web Services Composition (2008)
• [泛讀2] Measuring Reliability of Applications Composed of Web Services (HICSS, 2007)

[泛讀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)對Web服務組合進行建模(基於工作流程結構, 如順序, 並發等). 服務用庫所(place)來表示, 不同的遷移(transition)代表格服務執行是否成功, 每個遷移以一定的機率(這個機率跟該服務的reliability有關)被觸發(fired). 這樣組合服務可以用一副Petri Net表示出來(文中稱為CSPN, Composite Service Process Net model). 使用相關工具(比如snpn), 就可以計算出這個組合服務的reliability.

    作者鐘讀杭單位是國防科技大學, 他之前有一篇lncs的論文(Duhang Zhong, Zhichang Qi: A Petri Net Based Approach for Reliability Prediction of Web Services. OTM Workshops (1) 2006: 116-125)討論相同問題的, 本文新加了sensitivity analysis這部分, 討論了成員服務的reliability變化和usage profile變化對組合服務reliability的影響.

[泛讀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

    這個夏威夷的會議已經開了40多屆了, unrank, 看起來是個旅遊會議(50%左右的接收率) , 今年的截稿日期已經過了(June 15).

    這篇論文有10頁, 不過看下來覺得實質內容很少. 主要是在討論群組合服務的reliability計算, 使用了遺傳演算法進行服務選擇. 以下是論文筆記:

1. 作者對Midwest地區的IT architects進行調查, 關於選擇Web Service時何種QoS屬性最被看重. , Reliability最重要.

 

2. 關於reliability的定義
對於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.

本文對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) 本文採用了Cardoso提出的reliability的彙總方法(基於工作流程). 並假設服務之間的reliability是互相獨立的.

4. 對這篇論文有2個疑問
(1) (S3)中提到要"decompose business process into sub-processes", 但是後來並沒有將如何decompose, 只在(S5)中舉了一個已經decompose好的例子.
(2) 本文只考慮服務組合的一個QoS屬性(即reliability), 如果只考慮一個QoS屬性的話, 那麼針對每個task的最優解就能構成組合服務的全域最優解, 那還有必要用遺傳演算法來求近似解嗎?