The first step in decomposing a problem functionally is to represent it as a single black box operating on material ,
energy, and signal flows, as shown in Exhibit 7-4(a). Thin solid lin es denote the transfer and conversion of energy, thick solid lines signify the move ment of material within the system , and dashed lines represent the flows of control and feedback signals with in the system. This black box represents the overall function of the product.
The next step in functional decomposition is to divide the single black box into subfunctions to create a more specific description of what the elements of the product might do in order to implement the overall function of the product. Each subfuncti on cangenerall y be further divided into even simpler subfunctions. The division process is repeated until the team members agree that each subfunction is simple enough to work with. A good rule of thumb is to create between 3 and I 0 subfunctions in the diagram. The end result, sh own in Exhibit 7-4(b), i s a function diagram containing subfunctions connected by energy, material , and signal flows.