  Prospective studies require discussing and collaborating with the
stakeholders to create scenarios of the possible evolution of the studied
value-chain. However, stakeholders don't always use the same words when
referring to one idea. Constructing an ontology and homogenizing vocabularies
is thus crucial to identify key variables which serve in the construction of
the needed scenarios. Nevertheless, it is a very complex and timeconsuming
task. In this paper we present the method we used to manually build ontologies
adapted to the needs of two complementary system-analysis models (namely the
"Godet" and the "MyChoice" models), starting from interviews of the agri-food
system's stakeholders.
