The growth of web service formats over the Internet is increasing. These services should often be composed to achieve a user request. We propose in this paper a framework to cope with web service composition, from discovery to optimization. This framework, called SPOC, is composed of four successive phases: discovery, planning, quote execution and optimization. Only RFQ (Request for Quote) web services are treated in this first version of SPOC. The Discovery phase aims to search for web services in a repository. The Planning phase determines which services satisfy the user request. The Quote Execution phase involves processing a Request For Quote (RFQ) by calling web services. The last phase optimizes these results giving tradeoff compositions. As a proof-of-concept example, we applied SPOC to public competition processes in Public Markets.