In recent years, service oriented systems that compose services in a loosely coupled manner, have emerged as a new paradigm to provide automated support for business processes. These process based composition and their support need to survive in a highly volatile environments under which the business operations are subject to continuous changes. Consequently, many approaches have been proposed to address the issue of flexibility support in business process enactment in order to facilitate the coupling with the business reality. However, it remains a challenge for researchers. In this paper we provide some requirements for process flexibility in the context of service composition and analyses existing approaches in workflow domain and in AI planification domain against these requirements. Some perspectives are addressed based on a practical experiment conducted with these approaches.