Visually executing workflow composition
The Web is increasingly being used by organisations as a means of providing services to businesses and individual clients. Therefore, the Basic Services (BSs) that organisations offer need to be more accessible, scalable and adaptive. In order to provide value added and inter-organisational services, an "Internet Middleware" which creates a mutual criterion for composing services between organisations is necessary. In light of this, the JOpera visual service composition environment was created to serve as an advanced workflow definition tool capable of monitoring and debugging. Using this tool, a workflow process can be modelled with various syntaxes and developers are able to employ a visual representation to depict interactions between services to be composed. The tool can be used to handle the whole lifecycle of a process beginning with the service library, where web services can be imported as reusable components. The developer may browse the library, choose a group of basic services and drag and drop them into a process. Following this, the developer can start defining interactions by drawing the data flow graph. In order to get an overview of the order in which the tasks were performed the user may view and edit the control flow graph. The data flow graph and the control graph are kept in sync, providing innovative model checking facilities useful for validating the composition. During runtime, the visual representation is marked with colour-coded information which indicates the current condition of task execution. Thus, developers can click on parameters to examine their current value. In addition, the tool can administer the group of distributed processes and manipulate their overall performance. It is capable of highlighting any failure that may occur in order to run the debugging facilities and interactively determine the reason for the error.
