The emerging paradigm of web services promises to bring to distributed computing the same flexibility that the web has brought to the publication and search of information contained in documents. This new paradigm puts severe demands on composition and execution of workflows that must survive and respond to changes in the computing and business environments. Workflows facilitated by web services must, therefore, allow dynamic composition in ways that cannot be predicted in advance. Utilizing the notions of shared mental models and proactive information exchange in agent teamwork research, we propose a solution that interleaves planning and execution in a distributed manner. This paper proposes a generic model, gives the mappings of terminology between Web services and team-based agents, describes a comprehensive architecture for realizing the approach, and demonstrates its usefulness with the help of an example. A key benefit of the approach is the proactive failures handling that ...