Experimental assessment of the effect of inheritance on the maintainability of object-oriented systems

In this paper, we describe an empirical investigation into the modifiabilit y and understandability of object-oriented (OO) software. A controlled expe riment was conducted to establish the effects of varying levels of inherita nce on understandability and modifiability. The software used in this exper iment consisted of a C++ system without any inheritance and a corresponding version containing three levels of inheritance, as well as a second larger C++ system without inheritance and a corresponding version with five level s of inheritance. For both of the systems, the application modelled a datab ase for a University personnel system. A number of statistical hypotheses w ere tested. Results indicated that the systems without inheritance were eas ier to modify than the corresponding systems containing three or five level s of inheritance. Also, it was easier to understand the system without inhe ritance than a corresponding version containing three levels of inheritance . Results also indicated that larger systems are equally difficult to under stand whether or not they contain inheritance. The results contained in thi s paper highlight the need for further empirical investigations in this are a, particularly into the benefits of using inheritance. (C) 2000 Elsevier S cience Inc. All rights reserved.