Masses of sensors and actuators are being deployed in our daily environments to provide innovative services for such spaces as parking lots, buildings, and railway networks. Yet, to realize the full potentials of these sensor network infrastructures, services need to be developed. Service development raises a number of challenges due to existing approaches that are often low level and network/hardware-centric. This paper proposes a high-level approach to the development of large-scale orchestrating applications. It revolves around a declaration language that allows to express the sensor-network dimensions of an application (sensor discovery, delivery models, actuation process). These declarations define the behavior of an application with respect to the sensor network infrastructure. We demonstrate the key relevance of these declarations at every stage of an application lifecycle, from design to runtime. In doing so, declarations allow to match the sensor-network behavior of an application to the target infrastructure. Our approach summarizes and puts in perspective our development of industrial case studies and our experience in using a commercially-operated sensor infrastructure.