Design Space

Design Space and Evaluation Space We will start first with a simple model of design activity In this process, there are two stages: a design stage, and an evaluation stage:

Design

Evaluation

Figure 1. A simple model of a design process. The open circle represents a start state, and the closed circle an end stage.

Several designs are created, then evaluated. After evaluation, the design process continues, seeking to improve on the best of what has been done before, or seeking to explore the design space more fully. Designs are compared in an evaluation space. This continues until one or several good-enough solutions have been found. This model is commonly discussed in practice, and, is, indeed, a process that can be automated: variations are generated by computer, sometimes using search with random components, and one or several designs are chosen in the end (Deb 2002). Moreover, it is also a simple description of the brainstorming process (Osborn 1963), in which ideas are generated and later evaluated, leading to a second stage of idea generation. What do we mean by design space and evaluation space? We will begin with a simplified example from the domain of package design, a domain in which our physical intuitions will provide a grounding for the abstractions we want to discuss. Specifically, we imagine ourselves as consultants being given the task of designing a cereal box for a food company. Suppose we conclude from the conversations that we have only two dimensions of freedom. Since the volume of the box is fixed, we can define solutions by changing the width or the height of the box (the depth can then be derived). Height and width are quite literally dimensions. That is, all of our possible designs can be expressed by different values of the height and width dimension.

1

A

height

B C

width Figure 2. Design space for a box design; each point, labeled A, B, C represents a design.

The important thing to understand about a design...