0 Cesare Pautasso Gustavo Alonso 2005 Journal of Visual Languages and Computing (JVLC) 16 1-2 119-152 Composing Web services into a coherent application can be a tedious and error prone task when using traditional textual scripting languages or emerging XML-based approaches. As an alternative, complex interactions patterns and data exchanges between different Web services can be effectively modeled using a visual language. In this paper we discuss the requirements of such an application scenario and we fully describe the JOpera Visual Composition Language. An extensive set of visual editing tools, a compiler and a debugger for the language have been implemented as part of the JOpera system with the goal of providing a true visual environment for Web service composition with usability features emphasizing rapid development and visual scalability. http://dx.doi.org/10.1016/j.jvlc.2004.08.004