Towards understanding the understandability of UML models

Metrics for conceptual diagram understandability are generally based on a particular modelling notation and do not consider multiple perspectives in arriving at measurable metrics. This paper aims to be a step towards integration of multiple perspectives of conceptual model understandability. We demonstrate how one can arrive at a suite of metrics for conceptual diagram understandability. We use a questionnaire based on a few selected metrics to gain insights on the relative impact of different perspectives (namely, the notation and aesthetic perspectives) on conceptual diagram understandability. The main result of this study is that given a particular modelling notation (UML) and novice modellers, certain aesthetic aspects seem to have a greater impact on perceived diagram understandability than the notation aspects. We conclude with a call for further research in order to draw valid conclusions about the overall impact of the aesthetic and notation perspectives on diagram understandability.