Informal models do not respect rigorous formalism. They are often free images, media for ideas, or
spontaneous means of communication. They are naturally used during meetings and facilitate sponta-
neous communication. During early analysis phases, where the problem has not yet been clearly estab-
lished and consensus is needed to scope the area of intervention and the work to be carried out, or where
there is a need to communicate with participants who have no experience of the models used, informal
models can be used.