Client-Side Implementation of Dynamic Asynchronous Invocations for Web Services

Web Services are becoming more and more fundamental building blocks of Web-based distributed applications and a core technology for grid systems. Due to their flexibility, Web Services easily combine, in a common and coherent framework, ubiquitous computing with heterogeneous applications composed of different kinds of resources and, typically distributed in many organizations. We expect that this technology will follow the same evolution paths that have characterized other technologies so far, with some specificity due to the openness and size of the application context. In this connection, optimizations tied to invocations and workflows are assuming a primary role in Web Services research. The synchronous request/reply nature of the most diffused underling protocol (HTTP) introduces several restrictions in many application scenarios. On the other hand, asynchronous interactions are allowed by using message oriented middleware platforms, like JMS, which are typically harder to handle than object- and process-oriented middleware. In this paper, we propose a first implementation of a module that allows for dynamic Web Services invocations, which, on the basis of metadata added to WSDL, is able to select the most appropriate invocation technique for calling a Web Services operation.