Developing such a model also improves our understanding of design and challenges some of the theoretical developments in CD.
In order to effectively apply CD to design, it helps to do a task analysis of design problem solving. Design process models begin to identify some of the computational models of design and the implications of implementing one of them. Such models can provide guidelines in the development and use of computer support tools. Three models considered in this chapter include a decomposition approach to design, a CD approach, and a transformational approach.
Design, as ill-structured problem solving that has formal knowledge as well, presents challenges to the application of CD. Using CD requires the formalization of design experiences as a design case memory and the formalization of the reasoning processes of recall and adaptation. There are aspects of a design domain that have no formal representations, where the basics of CD cannot be applied as a formalism. There are also aspects of a design domain that may already be formalized and these formalisms need to be integrated with the CD model in order to have an effective design support tool. The idea of a hybrid CD system is defined and introduced in this chapter and is presented in more detail in later chapters.
Considering the implementations of CD in design problem solving shows the variety of applications of the same computational model. CD has been applied to the design of mechanical devices, the design of a meal, architectural and structural designs of buildings, and the design of computer programs. There are similarities in the use of CD in these domains, and there are significant are significant differences. A brief review of a selection of implementations of CD to design is included in this chapter. The purpose of this review is to introduce a variety of approaches to the application of CD to design; the rest of the book focuses on a subset of these approaches.
DESIGN PROCESS MODELS
Design is characterized as an ill-structured problem in several aspects. First, the problem definition is incomplete. As design proceeds, the definition of design problems changes. The formulation of design problems is, therefore, dynamically refined. Design also appears to be ill-structured, in the sense that there is no straightforward process to be followed. The imprecision of pertinent design knowledge can be viewed as another aspect of the ill-structured nature of design. Design theories and principles are often insufficient to guide the design process. During designing, therefore, the formulation of the design problem is dynamically modified as design progresses; multiple types of design knowledge, such as design theories, heuristics, and past design experience, are combined to compensate for the insufficient domain knowledge.The design process, although ill-structured, can be formalized at a high level of abstraction ( Simon, 1973). The selection of a formalization depends on the intended role of the resulting model, as there are many ways to characterize, dissect, and order design processes ( Dym, 1994). For the purpose of establishing the relevance of CD to the broadly defined process of design, the design process is considered as comprising three phases: formulation, synthesis, and evaluation:
Design formulation involves