In a general overview, sensing can be de‘ned as the process of knowing speci‘c information about the system of interest. With this general de‘nition, we can include human inspection as a sensing activity. A more technical de‘nition of sensing is that it is a process where sensors interrogate (interact) the system, and produce certain information about the state of the system. We have thus identi‘ed several components in the sensing process: (a) the sensors, (b) the information, (c) the system. The sensors are those vehicles that will detect the state of the system and produce the appropriate information to the user. The information (de‘ned later as type of measurements [ToM]) is transmitted to end user by the sensors: they describe speci‘c states of the system. The system is the infrastructure on hand, or any component within it. Figure 5.1 shows this relationship.