Recently, Sensor Networks (SNs) have become an emergent technology for various applications areas such as security and surveillance applications, traffic control, logistics, energy control in public and private buildings, etc. However, designing and constructing new applications using these technologies are still a very hard task. There is no standard API to access to the large variety of sensors and actuators which have also very different functionalities and capabilities. Applications are in general very specific and tightly coupled with the underlying infrastructure. Reuse is also very difficult or even impossible. This paper aims to provide a high-level environment based on a three levels model to program such infrastructure. At the lower level, sensors and actuators are encapsulated by lightweight web services, accessible through gateways. On top of this layer, abstract blocks denote sensors and actuators participating in the composite service along with a semantic description. Finally, these blocks are orchestrated as abstract graphs describing complex applications. This environment has been prototyped using service standards such as BPMN and BPEL within the context of the VITRO European project and validated by several use cases.