Business process design for real-world applications often requires modelling languages of a certain complexity, interweaving several process perspectives, such as the data and the organizational one, and taking contextual process information into account. Ensuring that such languages are indeed usable is not trivial. This paper describes a usability study for a modelling language with those characteristics. More specifically, the so-called BTG! language features the security concept Break the Glass (BTG) that allows to specify exceptional access to data.
We investigate usability characteristics of BTG! such as learnability, efficiency, errors, and satisfaction. Our study has helped to increase the usability of the language significantly. To illustrate, we have replaced the language terms with more intuitive ones and have extended the language with some frequently desired features. Our experiences can be applied to process modelling languages that are similarly comprehensive.