Description

A wireless sensor network (WSN) sometimes called a wireless sensor and actor network (WSAN) are spatially distributed autonomous sensors to monitor physical or environmental conditions, such as temperature, sound, pressure, etc. and to cooperatively pass their data through the network to a main location. The more modern networks are bi-directional, also enabling control of sensor activity. The development of wireless sensor networks was motivated by military applications such as battlefield surveillance; today such networks are used in many industrial and consumer applications, such as industrial process monitoring and control, machine health monitoring, and so on. A sensor network is viewed as a distributed database that collects physical measurements about the environment indexes them, and then serves queries from users. A wireless sensor network is a network of distributed sensors grouped together to monitor physical or environmental conditions, like temperature, pressure, sound etc. and to pass their sensed values through the network to a main location cooperatively. This paper surveys the state of the art of the techniques used to manage data and queries in wireless sensor networks based on the distributed paradigm. A classification of these techniques is also proposed.