中文摘要：

根据Web服务中消息和行为的关系，Web服务被描述为面向消息的基于行为Petri网模型（Moap）．该模型包括消息域和服务过程，前者是服务协同以及和用户通信的通道，后者是基于Petri网的Web服务行为过程描述．Moap支持组合服务的重用，可以很好地描述可用服务的并行调用，另外元消息机制也有利于服务的自动组合．在Moap基础上，定义了服务组合系统和服务的协同；给出了服务自动组合规则，并证明了其有效性和完备性．最后，通过一个实例直观描述了服务组合系统的工作方式．

英文摘要：

Automatic Composition of Web services is one of the most important issues in the research of service-oriented computing （SOC）. According to the relationship of messages and activities, Web services are defined as message oriented activity based Petri net model （Moap）. The model is characterized in terms of message domain and service process. The formal is used to the service cooperation and the communication with client; the latter is the description of Petri net based service process. Moap supports the reuse of the composite services. Compared with automata based models, Moap can describe parallel composition and the meta-message mechanism benefits the automatic composition. Based on Moap, the problem of service composition is presented including the definition of composite Web service system and the service cooperation. Then, the rules of automatic service composition are proposed and the soundness and the completeness are proven. Finally, an example also proofs the usability of Moap.