UML Class Diagram Syntax: An Empirical Study of Comprehension

Despite UML being considered a software engineering standard, the UML syntactic notations used in texts, papers, documentation and CASE tools are often different. The decision as to which of the semantically equivalent notational variations to use appears to be according to the personal preference of the author or publisher, rather than based on any consideration of the ease with which the notation can be understood by human readers. This paper reports on an experiment that takes a human comprehension perspective on UML class diagram notational variants. Five notations were considered: for each, two semantically equivalent, yet syntactically different, variations were chosen from published texts. Our experiment required subjects to indicate whether a supplied specification matched each of a set of experimental diagrams. The results reveal that the best performing notation may depend on the task for which it is used, and that our personal, intuitive predictions intuitions (which were based in the complexity of the notation) were partly confirmed.