Service portals are systems which expose a bundle of web services to the user, allowing the specification and subsequent execution of complex tasks defined over these individual services. Examples of situations where service portals would be valuable include making travel plans or purchasing a home. Service portals must be capable of converting an abstract user goal into a correct and optimal concrete execution plan, executing according to the plan, verifying the result against a user?s stated satisfaction criteria, and in the case of satisfaction failure, initiating the appropriate recovery procedures. The basic framework needed to support this functionality, from gathering the input to generating an optimal plan and executing that plan, is a prerequisite for all service portals, yet there are currently no such commercial systems in existence, and the research literature has given only cursory treatment to some of these issues. In this paper, we describe FUSION, a comprehensive software system which provides the underlying framework for a service portal. We show how using the elements of this framework, service portal designers and architects can easily create domain-specific service portals, e.g., a travel service portal. We also present the Web Services Execution Specification Language (WSESL), a language that we have developed to describe execution plans in the context of the FUSION services model. Finally, we develop a set of data structures and algorithms for generating correct and optimal execution plans.