An Empirical Study Evaluating Depth of Inheritance on the Maintainability of Object Oriented Software

This empirical research was undertaken as part of a multi method programme of research to investigate unsupported claims made of object oriented technology A series of subject based laboratory experiments including an internal replication tested the e ect of inheritance depth on the maintainability of object oriented software Subjects were timed performing identical maintenance tasks on object oriented software with a hierarchy of three levels of inheritance depth and equivalent object based software with no inheritance This was then replicated with more experienced subjects In a second experiment of similar design sub jects were timed performing identical maintenance tasks on object oriented software with a hierarchy of ve levels of inheritance depth and the equivalent object based software The collected data showed that subjects maintaining object oriented software with three levels of inheritance depth performed the maintenance tasks signi cantly quicker than those maintaining equivalent object based software with no inheritance In contrast subjects maintaining the object oriented software with ve levels of inheritance depth took longer on average than the subjects maintaining the equivalent object based software although statistical signi cance was not obtained Subjects source code solutions and debrie ng questionnaires provided some evidence suggesting subjects began to experience di culties with the deeper inheritance hierarchy It is not at all obvious that object oriented software is going to be more maintainable in the long run These ndings are su ciently important that attempts to verify the results should be made by independent researchers Daly is now with the Fraunhofer Institut IESE Kaiserslautern Germany