2.2 AGENTS OF SYSTEMATIC DESIGN
2.2.1 THE ANALYSIS, SYNTHESIS, AND EVALUATION PARADIGM
At the most abstract level, the act of design may be considered to be that of idea formation and idea communication. Indeed, any act of the human intellect could be summarily categorized in these terms. A description of design activity at this level does not offer great insight, but can be chosen as the means with which to systematically explore the components of design and the creative process that design entails.
A method of systematic design was offered by J.Christopher Jones in 1963 [Jones 63]. Jones asserts that a good design process involves the three consecutive steps of analysis, synthesis, and evaluation (ASE). The analysis step involves formulating design requirements and performance specifications. The following synthesis step involves determining appropriate solutions for both the individual specifications and the combination of specifications. The next step involves the evaluation of the current stage of design in the accuracy with which the performance requirements were actually fulfilled.
In 1975, Frederick Brooks offered similar concepts in specific terms of software engineering [Brooks 75]. His approach comprised the three steps of conceptualization, implementation, and interaction. Conceptualization, similar to Jones's analysis, requires the development of a functional specification. At this level, the outright behavior and performance requirements are determined and documented.
Actual details in Brooks's approach are accomplished in the implementation step, where development, coding, and integration are of appropriate concern. The next step is that of interaction, that is, how the software manifests itself to the user as a functioning entity operating to given specifications.
While the tools of design have undergone a dramatic evolution since Jones's and Brook's time, the inherent methodology behind the creation of a product remains steadfast. In recent years, with the application of artificial intelligence, efforts have been renewed upon the study of the activity of design and the development of models to describe it.
A comprehensive taxonomy of design research was developed by [Konda et al 92] which breaks design studies into those of process and those of the artifact. Of the process, the taxonomy is broken down into descriptive and prescriptive, the latter category of which Brooks and Jones belong. Recent research on the use of A.I. in design suggests that paradigms similar to the ASE paradigm, such as "propose, critique, and modify", are amenable to the enhancement of the design process [Brown & Chandrasekaran 89][Coyne 90][Dasgupta 89].
Table 2 outlines the stages of systematic design along with Brooks' method. Figure 6 depicts these stages of design as an iterative cycle. At first, the design requirements are analyzed and a conceptualization of design alternatives occurs. Decision between these alternatives is made by which the design is implemented within the synthesis stage, the design is then interacted with in the evaluation stage. The analysis stage is once again entered as portions of the design are reconceptualized in terms of the design space.
It is important to note that the analysis/conceptualization phase are in terms of the design space. Analysis is of the requirements and specifications of all considered engineering domains, and not specifically of the design itself. Although the design artifact will be argued to be best positioned at the center of the design process, analysis here is meant as evaluation and advice-making in terms of the design environment of which the design is a part.
Table 2 Stages of Systematic Design
Systematic Software
Design Design Description
Analysis Conceptualization Analysis of design space, with determination of and/or modification of design requirements and performance specifications.
Synthesis Implementation Proposal of solutions for individual specifications within the design and the combination of those specifications into a design artifact.
Evaluation Interaction Critique accuracy with which performance requirements are fulfilled within the design.
Figure 6 Stages of Systematic Design
Organizational and temporal constraints on the design cycle have been dramatically loosened over the years by computing technology. But the three steps of artifact creation may have more to do with the human formation and communication of ideas than with the organizations and tools available at a given time.
At this point, the formalisms exposed may be taken from two perspectives. They may be prescriptive, with the formalisms certified through use and invoked as a methodology for good design. Or these abstractions of the process may be deemed descriptive, having hit upon a common cognitive mechanism in the human act of creation.
While not ruling out the descriptive properties of this design cycle, attention is turned to the manifestation of these processes, specifically in terms of mapping these stages onto representations usable for the automation of the creative act.
Assuming a tractable boundary between the design steps, there must be a flow of information between these processes. For purposes of further discussion, this information between the processes shall be characterized as advice, design, and criticism. Figure 7 illustrates these communicative representations. While the names may seem too narrow, they are chosen to limit the connotations that may be invoked by other choices. As shall be seen, the definition of these representations will be expanded sufficiently.
The output of the implementation process is the design-as-artifact, the recorded representation of design solutions in a form from which other artifacts, physical or otherwise, can be produced. This design is evaluated in the interaction step, with the result of the evaluation - some indication of how well the design has met its requirements - stored as a critique. It is important to note here that interaction with the design is never an alteration of that design. The interaction is primarily an evaluation of what the design represents.
The conceptualization process of analysis may use the critique as a starting point for reconceptualization. In fact the initial conceptualization of a new artifact is always motivated by some criticism of an existing artifact or lack of such artifact.
The output representation of the analysis process is the advice. Advice is a suggestion of what must be implemented to meet specifications. Often, the advice is able to be implemented as-is, but the details from advice to design representation are handled in the implementation process.
Figure 7 Systematic Design Stages and Intermediating Representations
