一个基于偏序事件结构的Web服务模型及其形式化组装

随着Internet的发展，服务化和Web化趋势使得一个基于Web的分布式软件服务计算环境正在形成；同时随着大规模应用需求的不断涌现，单个的Web服务往往不能很好地满足一些复杂的应用。因此Web服务之间的集成组装就显得尤为重要。分析Web服务的交互和协同行为可以发现，分布性和并发性是基于软件服务分布计算系统的本质特征。这就往往使得组装的正确性难以得到保证，从而需要提供一定的手段加以支持；同时，基于软件服务分布计算系统的效率问题也值得关注。我们认为，利用偏序关系对这些问题加以处理是一种理想和有效的手段；而同时我们发现，在服务的组装中，服务与服务之间存在着一种自然的偏序关系。本文基于此，从形式化的角度研究了软件服务及其组装，提出了一种基于偏序事件多集的Web服务的形式化模型。本文从服务内部事件而不仅仅是服务的角度来考察并发问题，这使服务内和服务问的更多的事件可以并行执行，并使得组装后的系统可以更高效地进行实施，从而使得Web服务的并发拉度变细；在此基础上给出了一种服务组装语言和规则，以确保在组装过程中出现的局部变化不影响整体的Web服务的正确组装，从而能够从形式化的角度来规范Web服务的集成组装，使其正确性和效率能够得到保证。

A Web Service Model Based on Partial Order Event Structure and its Formal Composition

with the development of Internet, a software service computing environment based on Web has come into being. At the same time, as the requirement of large-scale applications, it is often not sufficient for single Web ser- vice to support some complicated applications. As a result, the composition of Web services becomes even more im- portant. Due to the interaction and coordination between Web services, distribution and concurrency are two essential characteristics of the software service distributed system, which makes it difficult to ensure the correctness of the composition. Thus a mechanism supporting composition should be provided. Moreover, the efficiency of the software service distributed system is also worth considering. This paper investigates these problems from the point of formal- ism. Partial order relation, as an ideal and effective means, is utilized because of the natural partial order relation a- mong Web services. Based on this, this paper gives a formal model of Web services based on partial order event mul- tisets from the perspective of composition. We deal with the concurrency problem from finer grain of event inside the Web service itself other than the whole Web service, which makes it possible for more events in one Web service or from different Web services to execute concurrently and thus improve the efficiency. Furthermore, a Web service composition language is given with the rules that ensure an efficient composition when correctness is guaranteed. Some examples are invited to demonstrate the advantages of our model and composition approach.