Figure 1.2. V-diagram showing opportunities for model-based testing and analysis.
finite element models for structures ??“ and even build physical models (to test in
wind tunnels, etc.). Our model programs are analogous to the models used in other
branches of engineering.
Model-based analysis and testing are each useful in their own right. A project
might use either or both. Figure 1.2 shows several opportunities for using them,
but a particular project might take only one or two. We know of projects where
architects used model programs just to debug protocols early in the project, and
testing was performed in the usual way. We know of others where testers wrote
model programs just for testing components that had been specified and designed
in the usual way. Moreover, we can model specifications (by modeling the system
behavior visible to users) or designs (by modeling the behavior of components only
visible to developers) or both (as shown in Figure 1.2). It is not necessary to model
everything; projects typically focus their modeling efforts on the system behaviors
or components that are the most novel, critical, or intricate.
Although model programs can be helpful during specification and design, this
book emphasizes model-based testing. Many of our examples assume that an implementation
is already in hand or on the way, so the model is based on the implementation
(not the other way around).
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