It is now widely accepted that formal methods are helpful for many issues raised in the web services area. In this paper, we advocate the use of process algebra as a first step in the design and development of executable web services. From such formal descriptions, reasoning tools can be used to validate their correct execution. We define some guidelines to encode abstract specifications of services-to-be written using these calculi into executable web services. As a back-end language, we consider the standard orchestration language BPEL. We illustrate our approach through the development of an e-business application.