Service composite

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Abstract. Service-oriented architectures define an architectural style for the construction of a heterogeneous application landscape. By abstracting services, business processes are decoupled from the underlying applications. This section describes how the results of the IMPROVE subproject 13, related to the model-driven development process for wrapper construction, are transferred and extended to the area of business process applications. We present an approach which yields a prototype to formally specify service descriptions and service compositions. This prototype makes it possible to evaluate and explore service-oriented architecture concepts. 

Figure 7.28 relates the layers of the architecture in Fig. 7.27 to the different phases of the extended model-driven wrapper development process [138]. While phases (l)-(5) (see Fig. 7.28 left) are already supported by corresponding tools we have developed (cf. Subsect. 5.7.4), phases (6) to (8) are new due to specifying service descriptions and service compositions and generating code for services. 

Finally, the service layer is modeled (phase 6 and 7 related to layer 4) and, again, the program code is generated (phase 8). Specifications for service descriptions and service compositions and their transformation into a programming language are not yet covered by our modeling formalism. They are one of the main scientific extensions of the approach, which will be introduced in the next subsection. 

Specifying service descriptions and service compositions causes the main extensions of our approach. 

The modeling formalism is enriched with concepts to model a service as a functional module, i.e. on the one hand to define the export and the import interface of the service service description), whereas imports are either other services or functions of business objects. On the other hand, the body of the service has to be specified. The body defines the control flow between the imports, i.e. sequences, alternatives, and loops of service or function calls with according execution conditions service composition). 

A precise conceptualization and a compact notation for modeling the aspects mentioned above is challenging. Furthermore, to determine suitable analyses for completeness and correctness of the models, so that program code generation is possible, is also not trivial. Both are interesting aspects of the extensions of the modeling formalism to specify service descriptions and service compositions. 

As already stated in Sect. 5.7, the modeling formalism for model-driven wrapper development is formulated as a graph rewriting system using the PROGRES language [412, 414]. Consequently, the necessary concepts to model service descriptions and service compositions will be implemented as an extension of the PROGRES specification shown in Fig. 5.60 on p. 571 and Fig. 5.67 on p. 586. 

Extensions of user interfaces mainly concern the implementation of different representations to visualize and to edit the static (service description) and the dynamic (service composition) aspects of the specifications. For example, to model service compositions several alternatives are possible (i) sequence diagrams, (ii) collaboration diagrams, or (iii) a textual notation in some kind of pseudo code. Which of them is the most appropriate alternative can only be determined through experiences using the prototype. The alternative views have to be implemented manually in JAVA and embedded into the UPGRADE framework as well. 

Thifien, D. Considering qos aspects in web service composition. In Proceedings of the 11 IEEE Symposium on Computers and Communications (ISCC 2006), Cagliari, Sardinia, Italy, pp. 371-376 (2006)... 

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