中文摘要：

进程代数可有效地用于Web服务组合的描述和验证，然而缺乏对服务组合成本建模和分析的能力．提出一种扩展了价格信息的进程代数PPA，在CCS基础上为进程动作和状态扩展价格函数，给进程动作的执行标记价格，给进程的迁移状态标记成本．给出了PPA的语法和语义，定义了PPA成本弱互模拟并分析了其与CCS弱互模拟的关系，证明了PPA在CCS基础上扩展了成本建模能力，给出了成本状态空间构造算法，该算法支持选择成本优化的组合服务．实验分析了PPA用于Web服务组合成本建模和分析的可行性．

英文摘要：

Process algebra includes a series of formal languages that are suitable to describe concurrent and communication systems including Web services. Nowadays, although process algebra has been effectively exploited for modeling and verification of Web service composition, only functional aspeets of Web service Composition have been addressed, and non-functional aspects have been ignored due to the fact that process algebra lacks for capability of modeling them. Since quality of serviee （QoS） of Web services composition is an important non-functional aspect and may include many quality attributes, such as resource, time, fee, etc, an abstract concept, which is cost, is proposed to model quality attribute. CCS（calculus of communicating systems） that is a classical process algebra with this abstract concept is extended, and a new process algebra called PPA（priced process algebra） is proposed. In PPA, actions and states of a process are associated with a priced function respectively. By this way, each action can be tagged with price and each state can be coupled with cost. Syntax and semantics of PPA are then presented. Cost weak bi-simulation of PPA is defined and relationship of it and weak bi-simulation of CCS is then presented. It is proved that PPA extends CCS with cost modeling capability. And an algorithm is proposed to construct cost state space that is used to select Web services composition with optimal cost. Experimental results show that PPA can not only model functional aspects but also non-functional aspects of Web service composition.