  This paper presents a qualitative study that investigates the effects of some
language choices in expressing the trigger part of a trigger-action rule on the
users' mental models. Specifically, we explored how 11 non-programmer
participants articulated the definition of trigger-action rules in different
contexts by choosing among alternative conjunctions, verbal structures, and
order of primitives. Our study shed some new light on how lexical choices
influence the users' mental models in End-User Development tasks. Specifically,
the conjunction "as soon as" clearly supports the idea of instantaneousness,
and the conjunction "while" the idea of protractedness of an event; the most
commonly used "if" and "when", instead, are prone to create ambiguity in the
mental representation of events. The order of rule elements helps participants
to construct accurate mental models. Usually, individuals are facilitated in
comprehension when the trigger is displayed at the beginning of the rule, even
though sometimes the reverse order (with the action first) is preferred as it
conveys the central element of the rule.
