(论文阅读) The Next Step In Web Services

Title　　　　　The Next Step In Web Services

Journal　　　　Communications of The ACM

Year　　　　　 2003

Author　　　　Francisco Curbera, Matthew Duftler .etc

Orgranization　IBM Research in Hawthorne, NY

Level                 Introductory

Comment          2002年作者有一篇” Unraveling the Web Services Web”, 这篇是后续。 本文主要介绍了3个协议：BPEL, WS-Coordination和WS-Transaction

1. 文章结构

• Introduce the initial trio of web service specification briefly and move to advanced specification
• Describe the key aspects of BPEL, WS-coordination and WS-transaction.
• Explain how these three specifications fit together to provide a framework for composing and coordinating distributed web services.
• Conclusion.

2. Claims

• Focus on the problem of creating service compositions and review how three specifications (BPEL4WS, WS-Coordination and WS-Transaction) support creating robust service compositions.

3. The Web Service Stack

4. Specifications beyond the basic framework

BPEL4WS

           Provide a mechanism for defining service compositions in the form of choreographies of web services.

           choreography: describes a dance sequence that has been created with specific intent.

WS-Coordination and WS-Transaction

           For robust service interactions. Complement BPEL to provide mechanisms for defining specific standard protocols for use by transaction processing systems, workflow system, or other applications that with to coordinate multiple web services.

WS-Security

WS-ReliableMessaging

WS-Policy

           extends WSDL to allow the encoding and attachment of Qos information to services in the form of reusable service “policies”.  

5. BPEL4WS

(1) Each BPEL composition is a business process or workflow that interacts with a set of web services to achieve a certain goal.

       BPEL composition is called process.

       The service the process interacts with is called partner.

(2) Core of a BPEL process composition:

        The definition of the message exchanges that take place between the process and each one of its partners.

(3) Fault handling and Compensation

        Fault handling provide a structural model to deal with error occurring within the process; the model is similar to “try-catch” blocks in Java.

       Compensation: “undo” the effects of actions that have already been completed.  

6. WS-Coordination

        A general framework for implementing specific coordination types, where the coordination of web services requires a shared context.

一种用来实现特定协同类型的通用框架，web service的协同需要共享语境。 

7. WS-Transaction

      定义了两类协调类型：原子事务（atomic transaction）和业务事务（business transaction）

     关于WS-Coordination和WS-Transaction的介绍，参考“Web 服务领域中的事务，第 1 部分”(ibm developworks)