The effect of layout in the comprehension of design pattern roles in UML class diagrams is assessed. This work replicates and extends a previous study using questionnaires but uses an eye tracker to gather additional data. The purpose of the replication is to gather more insight into the eye gaze behavior not evident from questionnaire-based methods. Similarities and differences between the studies are presented. Four design patterns are examined in two layout schemes in the context of three open source systems. Fifteen participants answered a series of eight design pattern role detection questions. Results show a significant improvement in role detection accuracy and visual effort with a certain layout for the Strategy and Observer patterns and a significant improvement in role detection time for all four patterns. Eye gaze data indicates classes participating in a design pattern act like visual beacons when they are in close physical proximity and follow the canonical layout, even though they violate some general graph aesthetics.
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