Many industries build sets of closely related products that have much functionality in common, yet each product contains some unique features. Such product families might be inventory control systems, telephone answering machines, application development tools, burglar alarm systems, and so on.
For example, suppose you are building a set of software products, each with some shared functionality, that may need to share data or otherwise communicate with one another when in use. In such a case, you might organize your requirements set with the following approach.
The resultant organization is shown in Figure 15-4.
Figure 15-4. Requirements organization for a software product family