One of Zeng liangzhao's classical papers, "quality driven Web Services Composition" (www03)

Zeng liangzhao is a bachelor at Sun Yat-sen University in China. His master's degree and PhD are both at the University of New South Wales (UNSW) in Australia and later at the IBM Watson Research Center. he wrote three papers on QoS-based Web Service combinations in 03 and 04, which are almost mandatory (sorted by order of publication ):
Liangzhao Zeng, Boualem benatallah, et. al: Quality Driven Web Services Composition (GS: 359). www 2003)
Liangzhao Zeng, Boualem benatallah, Anne H. H. Ngu et. al: QoS-aware middleware for Web Services Composition . (GS: 496) IEEE Trans. Software Eng. 30 (5): 311-327 (2004)
Yutu Liu, Anne H. H. Ngu, liangzhao Zeng: QoS computation and processing ing in Dynamic Web Service selection. (GS: 224) www 2004

The following are some of the papers published by Zeng LZ as the first author on dblp.
Event-driven Quality of Service prediction. icsoc 2008
Dynamic composition and optimization of Web Services. Distributed and parallel databases 24 (1-3) (2008)
Monitoring the QoS for Web Services. icsoc 2007
Semantic service mediation. icsoc 2006
Policy-driven exception-management for composite Web Services. CEC 2005
Agflow: Agent-Based Cross Enterprise Workflow Management System. vldb 2001

Quality Driven Web Services Composition notes
1. Modeling
This article uses statechart and Dag for modeling
The Service combination structure is sequence, concurrent, and condition. For loop, the average execution times of the loop are obtained based on historical data, so that the loop is "Unfolding" to eliminate the loop.
I did not mention more complex structures, such as 1-out-of-n (this should also belong to and state, but it is different from the synchronization condition when calculating some QoS) and WS have communication among them.

Statechart is used to model Web Service combinations. It is mainly used for intuitive demonstration.
Dag is used to model execution path, and later calculation and analysis are based on this.

2. Concepts involved in this article
Execution path
When a Service combination runs once, the involved task set (arranged in a certain order) (tasks can be considered Abstract Service) can be considered as a execution path.
If a ws combination has no condition branch, there is only one execution path. Otherwise, there are multiple execution paths.

Execution Plan
After the task in the execution path is instantiated, It is the execution plan.

WS community
A service set has the same functions and different QoS indicators. in the design phase, only ws community is specified for the task and a specific service is selected during running. in this way, the service selection is achieved during running.

Critical Path Algorithm (CPA)
In a directed graph, each node has a weight, specifying the start point and focus. CPA can find a path with the maximum weight and weight of all nodes in the path.
In this article, the concept of critical path is used for the execution duration and reliability of time QoS attributes (see the reliability definition in s3.1.

3. problem: the problem to be solved in this article is very clear. QoS-based Web Service Selection (in Web Service combination scenarios) is a basic problem in the Web Service combination field.
If you only consider one attribute of the web service, it is clear that the combination of WS is optimal for each task in the combination. However, in WS, there are multiple attributes (price, duration, in the case of reliability, different QoS attributes have different calculation methods in the combination structure (such as synchronization), and local optimal solutions cannot be used to obtain the global optimal solution.

4. (S4) is the focus of this Article. Several global service selection methods are discussed.
(s4.1) only scenarios where statechart does not contain conditional branching and the Service combination has only one execution path are discussed.
the saw method in MADM is used to normalize Qos attributes and add them to a score (each execution plan has a score ). (this evaluation method was later borrowed by many other ws selection papers)
(s4.2) based on s4.1, discuss the situation of multiple execution paths, the author does not theoretically explain that this method can select the global optimal solution.
1) Calculate the optimal solution for each execution path in a service combination using the method in s4.1
2) If a task only belongs to one execution path, then this task selects the service selected on this execution path.
3) if a task belongs to multiple execution paths, select the most selected ws.
(s4.3) use the linear programming (LP) method to find the optimal solution. LP has three inputs: variables, objective function, and constraints
for attributes such as reliability and availability, first, linearity is required.
problem : The author does not explicitly describe whether the LP method can have conditional branching for statecharts, however, from the formula (9), it should be solved only when there is no conditional branching. formula (9) indicates that for any task, only one WS is selected. if conditional branching exists, some tasks will not select ws. this issue needs further confirmation.

5. Implementation
Based on the SELF-SERV prototypeAlgorithm.
Use IBM Web Services toolkit 2.4 (wstk2.4) as a Web Service Development Tool

Call IBM's optimization solutions and Library (OSL) to solve LP Problems

6.Problem: (S4.3.1) "by introducting a budget constraint the above problem needs to be explicitly solved as an integer programming problem ".
Why is it necessary to explicitly define the IP address (Integer Programming) after the budge restriction is introduced? The value range of the yij variable is 1, 0 (indicating whether to select or not). Is it an IP address?
This is a special case of the knapsack problem, so it is NP-hard.
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Before the introduction of the Budge, there is no "backpack capacity" limit, so it is not a backpack problem, it may not be NP difficult.

7. errata
(S2.1) "note that when two transitions stem from the same State (in this case the State T4 )"
T4 in this sentence should be T5 (refer to QoS-aware middleware for Web Services Composition for details)

 
(S5.2 lab Verification Section) not detailed at the moment
 
Reading this level of paper consumes a lot of brain cells.