The current sensor networks are assumed to be designed for specific applications, having strongly coupled data communication protocols. The future sensor networks are envisioned as comprising heterogeneous devices assisting to a large range of applications. To achieve this goal, a new architecture approach is needed, having application specific features separated from the data communication protocol, while influencing its behavior. We propose a Web Services approach for the design of sensor networks, in which sensor nodes are service providers and applications are clients of such services. Our main goal is to enable a flexible architecture where sensor networks data can be accessed by users spread all over the world.