Towards a Principle-based Classification of Structural Design Smells

Fred Brooks in his book "The Mythical Man Month" describes how the inherent properties of software (i.e. complexity, conformity, changeability, and invisibility) make its design an "essential" difficulty. Good design practices are fundamental requisites to address this difficulty. One such good practice is that a software designer should be aware of and address "design smells" that can manifest as a result of his design decisions. However, our study of the vast literature on object-oriented design smells reveals the lack of an effective organization of smells that could better guide a designer in understanding and addressing potential issues in his design. In order to address this gap, we have adopted a novel approach to classify and catalog a number of recurring structural design smells based on how they violate key object oriented (OO) design principles. To evaluate the usefulness of our design smell catalog, we first asked Siemens CT DC AA architects to use it to identify design smells in their projects, and later elicited feedback from them about their experience. The feedback received indicates that these architects found the catalog to be very useful. In this paper, we present our catalog, classification, and naming scheme for design smells and also highlight several interesting observations and insights that result from our work.