  This paper reports on the results of the French ANR IMPEX research project
dealing with making explicit domain knowledge in design models. Ontologies are
formalised as theories with sets, axioms, theorems and reasoning rules. They
are integrated to design models through an annotation mechanism. Event-B has
been chosen as the ground formal modelling technique for all our developments.
In this paper, we particularly describe how ontologies are formalised as
Event-B theories.
