Design Strategies and Knowledge in Object-Oriented Programming: Effects of Experience

An empirical study was conducted to analyse design strategies and knowledge used in object-oriented software design. Eight professional programmers experienced with procedural programming languages and either experienced or not experienced in objectoriented programming participated in this experiment. They were asked to design a program for a procedural problem and a declarative problem. We have concentrated our analysis on the design strategies related to two central aspects of the object-oriented paradigm: (1) associating actions, i.e., execution steps, of a complex plan to different objects and revising a complex plan, and (2) defining simple plans at different levels in the class hierarchy. As regards the development of complex plans elements attached to different objects, our results show that, for beginners in OOP, the description of objects and the description of actions are not always integrated in an early design phase, particularly for the declarative problem whereas, for the programmers experienced in OOP, the description of objects and the description of actions tend to be integrated in their first drafts of solutions whichever the problem type. Most of the first drafts of solutions were structured around the objects, whatever the experience of subjects in OOP. However, by analysing the order in which actions are generated, we found that, for the programmers experienced in OOP, methods were grouped together mainly by membership to the same class whereas, for beginners in OOP, methods were grouped together mainly by functional similarity and execution order. Furthermore, with only a little experience in OOP complex plans are revised more often. As concerns the development of simple plans at different levels in the class hierarchy, our results indicate that with a little OOP experience, simple plans are developed either in a top-down manner or in a bottom-up manner. With more OOP experience, our results show that a simple plan is developed in a strictly top-down manner. The analysis of design strategies reveal the use of different knowledge according to subjects' language experience: (1) schemas related to procedural languages; actions are organized in an execution order, or (2) schemas related to object-oriented languages; actions and objects are integrated, and actions are organised around objects.