On the impact of layout quality to understanding UML diagrams

Practical experience suggests that use and understanding of UML diagrams is greatly affected by the quality of their layout. However, existing experimental evidence for this effect is been weak and inconclusive. In this paper, we explore two explanations. Firstly, we observe that the visual qualities of diagrams are more prominent in earlier life cycle phases so that the impact of layout quality should be more apparent in models and diagram types used there, an aspect not studied in previous research. Secondly, in practice, good layouts use many different heuristics simultaneously whereas previous research considered them in isolation only. In this paper, we report the results of a series of controlled experiments using compound layouts on requirements analysis models. With very high significance, we find a notable impact of the layout quality measured by different aspects of cognitive load.