Web service composition is recently receiving much attention as an important problem for the services oriented architecture community. There have been many planning methods for building compositions based on pre-defined models of the process environment. However, these methods have assumed that the information in the models remain static and accurate throughout the life cycle of the Web process. We describe an approach that captures the dynamic nature of web services by formulating a system that queries external sources intelligently. We use an approach that measures the value of change that a revised model parameter may potentially introduce. We provide an algorithm that calculates and uses this value to optimally adapt the Web process to possible changes in environment. Using a supply chain scenario, we demonstrate our idea and compare its performance to existing methods.