Z-devices can act independently - page 4 A thought question: Is the rain sensor a "part of" the windshield wiper? I have talked about a hierarchy of Z-devices, where one Z-device was "made up of" a number of "smaller" Z-devices. But do they really have to be "inside of" and "smaller than"? Of course not. We shall now blur the boundaries between "things". Instead of saying that the windshield wiper "is composed of" a motor, rain sensor, and other things, let us instead say that there are a number of Z-devices, such as a motor, a rain sensor, a wiper, a squirter, and other things, and they all can work together to perform various tasks. Not limited to being a physical part of the bigger object, these individual objects are free to cross functional lines to be "part of" more than one larger function. For example, the rain sensor may be used by systems other than the windshield wiper. The windows may also want to know when it is raining so that they can close! Or when the air-conditioner needs them closed. They may also decide to close if a burglar sensor activates. In other words, Z-devices are independent. They are not necessarily *part of* each other, but may participate in a multitude of functions *with* each other. And while their interactions may be complex, each object has only to do a very simple task. The wiper only needs to "compute" whether to wipe or not, and at what speed. The rain sensor has one tiny job, to put out a number from 0 to 100. The "wash button" only has to "decide" if it is being pushed or not. Each individual object has a very simple, sometimes trivial, task or algorithm. But when combined into a group, many more complex behaviors can emerge.