Nowadays, web services represent the technology that allows having independent platform and language components. A service oriented architecture promises to make ready creation of applications composed of dynamically selected components. In such a case, we take an interest in web service composition. Indeed, the composition appears as an important strategy to provide more complex and useful solutions. In this paper, we present an architectural framework for the web services composition. Our approach, called WesCO CBR (Web Service Composition founded on case-Based Reasoning), uses the case-based reasoning,that allows us to have a dynamic and intelligent composition. In this work, we are essentially interested in the construction of the composition diagram. To distribute WeSCo CBR, we propose to use a multi-agent system, that allows different sites to exploit others.