In the recent years, the idea of realizing software as a service is getting wide acceptance in the software engineering community. Web services are reusable software components which can be discovered and invoked using standard Internet protocols. The development and use of service oriented systems differ from the traditional approach used in other kind of Web applications. In this position paper we try to improve the development and evolution of service oriented systems. To achieve this we propose a modification of the traditional product line approach to support composite services. We use a lightweight product line with specific variability information to facilitate web service composition as well as the evolution of such systems.