If today someone uses a modern piece of equipment, for example a video recorder, an ATM, or a cell phone, he or she is rarely interested in how that piece of equipment looks from the inside. The average user does not care which electronic parts a machine consists of, or what software it includes. On the other hand, what the machine can be used for, or what functionalities it provides, is important to the user. For instance, the buyer of a cell phone wants to know if the device has WAP capability or how many addresses it can store. Usually, the potential buyer of a cell phone is interested in how the device can be used; he or she is not interested in how the device is built internally, as long as it has the desired functionalities.
This type of view of a system is called a black-box view, meaning the system or device is pictured as a black box—you cannot look inside. You don't know how it works; you only...