Software Engineering-Design Concepts and Principles


The designer's goal is to produce a model or representation of an entity that will later be built. The process by which the design model is developed is described by Belady :

There are two major phases to any design process: diversification and convergence. Diversification is the acquisition of a repertoire of alternatives, the raw material of design: components, component solutions, and knowledge, all contained in catalogs, textbooks, and the mind. During convergence, the designer chooses and combines appropriate elements from this repertoire to meet the design objectives, as stated in the requirements document and as agreed to by the customer. The second phase is the gradual elimination of all but one particular configuration of components, and thus the creation of the final product.

Diversification and convergence combine intuition and judgment based on experience in building similar entities, a set of principles and/or heuristics that guide the way in which the model evolves, a set of criteria that enables quality to be judged, and a process of iteration that ultimately leads to a final design representation.

Software design, like engineering design approaches in other disciplines, changes continually as new methods, better analysis, and broader understanding evolve. Software design methodologies lack the depth, flexibility, and quantitative nature that are normally associated with more classical engineering design disciplines. However, methods for software design do exist, criteria for design quality are available, and design notation can be applied. In this chapter, we explore the fundamental concepts and principles that are applicable to all software design.
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