We describe how contextual graphs allow the analysis of oral corpus from person-to-person collaboration. The goal was to build a task model that would be closer to the effective task(s) than the prescribed task. Such a “contextualized prescribed task” is possible, thanks to a formalism allowing a uniform representation of elements of decision and of contexts. The collaborative process of answer building identified includes a phase of building of the shared context attached to the collaboration, shared context in which each participant introduces contextual elements from his/her individual context in order to build the answer with the other. Participants in the collaborative building process agree on the contextual elements in the shared context and organize, assemble and structure them in a proceduralized context to build the answer. The proceduralized-context building is an important key of the modeling of a collaborative decision making process.