A Controlled Experiment in Maintenance Comparing Design Patterns to Simpler Solutions

Software design patterns package proven solutions to recurring design problems in a form that simpli es reuse. We are seeking empirical evidence whether using design patterns is bene cial. In particular, one may prefer using a design pattern even if the actual design problem is simpler than that solved by the pattern, i.e., if not all of the functionality o ered by the pattern is actually required. Our experiment investigates software maintenance scenarios that employ various design patterns and compares designs with patterns to simpler alternatives. The subjects were professional software engineers. In most of our nine maintenance tasks we found positive e ects from using a design pattern: either its inherent additional exibility was achieved without requiring more maintenance time or maintenance time was reduced compared to the simpler alternative. In a few cases we found negative e ects: the alternative solution was less error-prone or required less maintenance time. Although most of these e ects were expected, a few were surprising: a negative e ect occurs although a certain application of the Observer pattern appears to be well justi ed and a positive e ect occurs despite super uous exibility (and hence complexity) introduced by a certain application of the Decorator pattern. Overall, we conclude that unless there is a clear reason to prefer the simpler solution, it is probably wise to choose the exibility provided by the design pattern, because unexpected new requirements often appear. We identify several questions for future empirical research.