ABSTRACT Previous studies on program comprehension were carried out largely in the context of procedural languages. Our purpose is to develop and evaluate a cognitive model of object-oriented (OO) program understanding. Our model is based on the van Dijk and Kintsch's model of text understanding (1983). One key aspect of this theoretical approach is the distinction between two kinds of representation the reader might construct from a text: the textbase and the situation model. On the basis of results of an experiment we have conducted, we evaluate the cognitive validity of this distinction in OO program understanding. We examine how the construction of these two representations is differentially affected by the programmer's expertise and how they evolve differentially over time. KEY WORDS mental representation, situation model, program model, object-oriented programming, program comprehension, text comprehension, expertise 1. OBJECTIVES The object-oriented (OO) paradigm is growing fast in popularity, but not enough scientific evidence has been amassed about it. The research that exists is mostly focused on program design and reuse (see for example: Détienne, 1995; Pennington, Lee and Rehder, 1995).

The objective of this study was to determine whether the mental representation of object-oriented programs differs from imperative programs for novice programmers. In our study novices who had little or no previous programming experience studied and answered questions about three imperative and three object-oriented programs. The questions targeted information categories making up the program model and the domain model representations of the programs. It was found that there was a sharp contrast between the mental representations of the imperative and object-oriented programs. While the comprehension of the imperative programs was better overall than that of the object-oriented programs, the mental representations of the imperative programs focused on program-level knowledge. On the other hand, the mental representations of the object-oriented programs focused more strongly on domain-level knowledge. The results tend to support the view that language notations differ in how well they support the extraction of various kinds of information. 1.

Abstract. The goal of our study is to evaluate the effect on program comprehension of three factors that have not previously been studied in a single experiment. These factors are programmer expertise (expert versus novice), programming task (documentation versus reuse), and the development of understanding over time (phase 1 versus phase 2). This study is carried out in the context of the mental model approach to comprehension based on van Dijk and Kintsch’s model [(1983) Strategies of Discourse Comprehension. New York: Academic]. One key aspect of this model is the distinction between two kinds of representation the reader might construct from a text: (1) the textbase, which refers to what is said in the text and how it is said, and (2) the situation model, which represents the situation referred to by the text. We have evaluated the effect of the three factors mentioned above on the development of both the textbase (or program model) and the situation model in object-oriented program comprehension. We found a four-way interaction of expertise, phase, task and type of model. For the documentation group we found that experts and novices differ in the elaboration of their situation model but not their program model. There was no interaction of expertise with phase and type of model in the documentation group. For the reuse group, there was a three-way interaction between phase, expertise and type of model. For the novice reuse group, the effect of the phase was to increase the construction of the situation model but not the program model.