Exploring human factors in formal diagram usage

Formal diagrammatic notations have been developed as alternatives to symbolic specification notations. Ostensibly to aid users in performing comprehension and reasoning tasks, restrictions called well- formedness conditions may be imposed. However, imposing too many of these conditions can have adverse effects on the utility of the nota- tion (e.g. reducing the expressiveness). Understanding the human factors involved in the use of a notation, such as how user-preference and comprehension relate to the imposition of wellformedness conditions, will enable the notation designers to make more informed design decisions. Euler diagrams are a simple visualization of set-theoretic relationships which are the basis of more expressive constraint languages. We have performed exploratory studies with Euler diagrams which indicated that novice user preferences strongly conform to the imposition of all well- formedness conditions, but that even a limited exposure diminishes this preference.