| With strong portability and interoperability, Web services provide business by the use of Internet and SOAP. Web services can shield the distinction among heterogeneous systems. Users call applications and resources by providing the web interfaces, but the internal implement of services and resources is not involved. Web services are self-contained, self-describing modular applications that can be published, located and invoked. Combining the existing Web services into large Web services application is the aim of Web services technology. Service-Oriented Architecture (SOA) connects the Web services that have the ability to carry out tasks, in order to achieve the cross-platform, cross-language and loose coupling target.It is difficult to study Web service on how to describe Web services, realize automatic discovery and dynamic composition. Web Service description language (WSDL) [20, 22] is an interface description standard both in industry and academic. It describes Web Service as a group of interfaces which describe the property of the dynamic behaviors of Web Service, capable of achieving interoperability among the services. WSDL describes the interface in grammar. WSDL defines the concepts of the input and output types, but it does not support the logic between input and output parameters bound. Web services described by WSDL lack semantic, so it is hard for computers to understand, and WSDL doesn't support the automatic discovery of Web services.Pi calculus is the concurrency theory focus on mobile communication during processes, which is the development of Calculus of Communication System (CCS). In fact, the work on Pi-calculus really began with a discussion between Robin Milner and Mogens Nielsen at Aarhus in 1979. They discussed how the full mobility among processes could be handledalgebraically. Several years later, Engberg and Nielsen succeeded in giving an algebraic formulation. Pi-calculus is a simplification and strengthening of their work. Its basic computing entities are names and processes. The communication between the processes is completed by transferring names.The theory section of this paper explains the Web Service and its composition and process algebra. It provides a strong theoretical basis for the realization of PICM2WSDL. Firstly, this theory section introduces the basic concepts and characteristics of Web services, the three key techniques of releasing Web services, and the Web services architecture. This paper introduces the basic structure of the WSDL language and its content in details, and then describes Web services composition based on Pi-calculus. This paper explains some basic concepts of process algebra, including the definitions of process algebra syntax, operational semantics, equivalent rules, as well as simplify rules and so on. Finally, it gives an example to explain how to describe Web Service by Pi-calculus.The modeling section of this paper explains the design of the PICM2WSDL model. In order to converse the WSDL document to the Pi calculus expression of Web services, it's necessary to define channel name and massage name etc. in modeling. After the initial work, this paper carries out a structural analysis, definition and description of PICM2WSDL. After analyzing Web Service, this paper can identify the mapping between Pi calculus expression and WSDL document. Finally, this paper describes the significance of achieving PICM2WSDL, and proves the correctness of the translation between Pi-calculus-based Web services composition and WSDL.The realization section of this paper introduces the method of conversing Pi-calculus expression to WSDL document.It is necessary for the definitions of names and operations in modeling to provide an identification mechanism for PICM2WSDL. And then, thispaper needs to provide a name identification system which is more similar to the traditional sense of the lexical analysis. All operations in Pi-calculus, for example, transmitting parameters will be realized by names. PICM2WSDL requires that computers can distinguish which are channels, and which are massages. When it comes to names identification, identifying different prefixes will identify the categories of the names, which simplifies the process of the translation.After the name recognition, it is necessary to analyze Pi Calculus expression of Web services, and specify the operation relationship, this section explains analytical expression. Analytical expression is similar to traditional grammatical analysis, and the difference is that the expression is more complex than before. In traditional programming language, the complexity of expression in high-level languages is far less than the high expression of Pi Calculus. Therefore, this paper sums up some production according to Pi Calculus Grammar, and paves the way for analytical expressions.According to Pi calculus expression, it is also given a semantic analysis system of PICM2WSDL. This paper gives an algorithm of semantic binary tree to describe Pi calculus expression. This algorithm can produce a binary tree to describe the relationship among of all processes in Pi calculus expression.After all the preparatory work, the generation of the target document means the success of the whole work. This section describes the process of translating Pi-calculus expression to WSDL document and the results in details, through describing the earlier corresponding relationship, name recognition, expression analysis and semantic analysis.Finally, PICM2WSDL interface and the results are achieved. According to the needs of the clients, PICM2WSDL directly abstract WSDL files, and distributed them to UDDI, and it is more convenient for customersto use. To Web services that already exist, according to the simple message transferring graph, WSDL files could realize. This will reduce the work generated WSDL files.The ideal Web services composition assumes that all the atomic services already exist. However, only Web services in UDDI can be used, which means that some services do not actually exist, and they are abstract, then there will be the crux of the process composition, the composition has become meaningless. Through change, it needs to be completed from WSDL files, and register it in UDDI, and complete the whole services composition, which provides a great help to the composition.PICM2WSDL supports model automatic verification. Pi-calculus can be used to detect the problems in processes and services, such as deadlock and so on. It is necessary to translate Pi expression to WSDL document, which is only part of the automatic verification. To fully achieve automatic verification of the model, it still needs to realize the two-way conversion of process algebra and WSDL. |
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