1. Introduction
The paradigmatic shift from a Web of manual interactions to a Web of programmatic interactions by Web Services is creating unprecedented opportunities for the formation of online Business-to-Business collaborations. In particular, the creation of valued-added services by composition of existing ones is gaining a significant momentum. Since many available Web Services provide overlapping or identical functionality, albeit with different non-functional properties, a choice needs to be made to determine which services are to participate in a given composite service [1].