Design pattern decay: the case for class grime

Context: We investigate class grime, a form of design pattern decay, wherein classes of the pattern realization have extraneous attributes or methods, which obfuscate the intended design of a pattern. Goal: To expand the taxonomy of class grime using properties of class cohesion. Using this expanded taxonomy we explore the effect that forms of class grime have on pattern realization understandability. Method: A pilot study utilizing a formal experiment to explore the effects of class grime on design pattern understandability. The experiments used simulated injection of 8 types of class grime into design pattern realizations randomly selected from 16 design pattern types from a set of 6541 realizations from 520 distinct software systems. Results: We found that for each of the 8 identified class grime forms, understandability was negatively affected. Conclusion: This work serves as early communication of research for the validation of the extended taxonomy as well as the method of grime injection used in the experiment.