Evaluation is establishing the ‘value’ or ‘quality’ of the provisional design. To do so, the expected properties are compared with the desired properties in the design specification. As there will always be differences between the two, it will have to be judged whether those differences are acceptable or not. Making such a value judgment is difficult, for usually many properties, while it is weak in others.
Decision
Then follows the decision: continue (elaborate the design proposal) or try again (generate a better design proposal). Usually the first provisional design will not be bull’s eye and the designer will have to return to the synthesis step, to do better in a second, third or tenth iteration. But you can also go back to the formulation of the problem and the list of requirements. Exploring solutions appears to be a forceful aid to gain insight into the true nature of a problem: you might therefore often want to adjust, expand, or perhaps sharpen up specification are thus further developed in successive cycles and in a strong interaction, until they fit one another.
This iterative, spiral-like development of the design and the performance specification has been reflected in figure 2. The design process comprises a sequence of intuitive (reductive)steps and discursive (deductive) steps. Between the two, there is always a comparison of the results attained so far and the desired results. The experience gained in the cycle is fed back, both to the design proposal and to the formulation of the problem and the list of requirements.
References and Further Reading