Functional Prototyping

If your prototyping goals are such that only a functional prototype will do, you are going to have to write some code. Again, you need to have proper, realistic, specific goals for creating your prototype. For a functional prototype, you should try to accomplish your goals by writing as little code as possible. Restraint is essential. Consider establishing a strict time limit for the creation of a functional prototype, such as a week at most. Unbounded functional prototypes rarely have benefits that justify their costs. The best way to get useful information from functional prototyping is through user testing, as described in Chapter 27.

There are two basic types of functional prototypes. A horizontal prototype implements most of the major functionality but with very little depth. Such a prototype gives a good feel for what the appearance of the program as a whole will look like, but the individual features might lack significant functionality if they work at all. By contrast, a vertical prototype implements enough features to perform a single task or a small set of tasks but doesn't attempt to implement the remainder of the program. Such a prototype gives an accurate model of the ability to perform those tasks but little else. Of course, it is possible to combine these techniques and create a horizontal prototype with enough features implemented to perform a few tasks.

TIP

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If you must create a functional prototype, try to implement as little functionality as you can. Create either a horizontal or vertical prototype and establish a strict time limit.