Nowadays, Web services allow interoperability among distributed software applications deployed on different platforms and architectures which in effect plays a major role in electronic businesses. Web services allow organizations to carry out certain business activities automatically and in a distributed fashion. However, in some circumstances, a single service is not able to perform a certain task and it becomes imperative to compose two or more services in order to complete it. Thus, a key research challenge in this field is the problem of automatic service composition. Several approaches exist that tackle the problem of automatic service composition, however, the task of generating provably correct Web service compositions still remains a challenging and complex task. In this paper, we develop a formal framework for modeling Web service compositions based on Supervisory Control Theory (SCT) of discrete-event systems. We model services that exchange messages and exhibit nondeterministic behaviours. The objective is to synthesize a supervisor which interacts with a given set of Web services through messages to guarantee that a given specification is satisfied. A key novelty of this work is the application of control theory to service-oriented computing and the incorporation of run-time input into the supervisor generation process. First, we describe a novel supervisory control framework for automated composition of Web services. The framework employs Labelled Transition Systems equipped with guards and data variables to model Web services and provides a technique to synthesize a controller. We model the interactions of services asynchronously and we use the guards and data variables to allow us to express certain preconditions which are then propagated from the system requirements through the overall composite service. Second, we develop a set of algorithms to generate a controller satisfying a given functional requirement also specified as a Labelled Transition System equipped with guards and data variables. Besides the standard disabling and enabling of events, the generated controller in our framework has the ability to enforce certain events based on run-time information to drive the system towards its goal. In addition, the controller is able to impose restrictions on the kind of data that can be sent or received by services. This includes the automatic generation of stronger guards or preconditions which impose restrictions on which path to take during execution. Lastly, we state a theorem capturing the existence of a controller and provide a proof to demonstrate the correctness of the proposed approach.

中文翻译：

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用于自动化服务组合的控制器合成框架

如今，Web 服务允许部署在不同平台和体系结构上的分布式软件应用程序之间具有互操作性，这实际上在电子商务中发挥着重要作用。Web 服务允许组织以分布式方式自动执行某些业务活动。但是，在某些情况下，单个服务无法执行某个任务，必须组合两个或多个服务才能完成它。因此，该领域的一个关键研究挑战是自动服务组合问题。存在多种解决自动服务组合问题的方法，但是，生成可证明正确的 Web 服务组合的任务仍然是一项具有挑战性和复杂性的任务。在本文中，我们基于离散事件系统的监督控制理论 (SCT) 开发了一个用于建模 Web 服务组合的正式框架。我们对交换消息并表现出非确定性行为的服务进行建模。目标是合成一个通过消息与一组给定的 Web 服务交互的主管，以保证满足给定的规范。这项工作的一个关键创新是将控制理论应用于面向服务的计算，并将运行时输入纳入监督生成过程。首先，我们描述了一种用于自动组合 Web 服务的新型监督控制框架。该框架采用配备有保护和数据变量的标记转换系统来对 Web 服务进行建模，并提供了一种合成控制器的技术。我们对服务的交互进行异步建模，并使用守卫和数据变量来表达某些先决条件，然后将这些先决条件从系统需求传播到整个复合服务。其次，我们开发了一组算法来生成满足给定功能要求的控制器，也指定为配备有保护和数据变量的标记转换系统。除了标准的事件禁用和启用之外，我们框架中生成的控制器还能够根据运行时信息强制执行某些事件，以驱动系统实现其目标。此外，控制器能够对服务可以发送或接收的数据类型施加限制。这包括自动生成更强大的保护或先决条件，这些条件对执行期间采取的路径施加限制。最后，我们陈述了一个定理来捕捉控制器的存在，并提供一个证明来证明所提出方法的正确性。