The synthesis of complex systems

In systems synthesis the basic lesson-and the hardest to accept-is that not all engineering problems can be or should be solved by deduction from mathematical and scientific principles. Synthesis is provisional and qualitative, a way of thinking different from the definitive, quantitative thinking of analysis. Its technique and tools reflect this difference. In synthesizing the system's initial concept, three qualitative techniques are fundamental: heuristics, metaphors, and models. Heuristics are brief statements of lessons learned in the past and applicable to the present situation. Metaphors transpose the implicit behavior of a system to a more familiar context, one example is the desktop metaphor for personal computer operating systems. Models are used to present different perspectives of a proposed system to multiple stakeholders so that everyone has a common frame of reference for discussion. Progressive modeling emphasizes the continuing refinement of models during system development than, say, an initial sketch to full-scale simulator. Each of these qualitative techniques are discussed.