In the present paper we propose a theoretical framework for an epistemological modelling of teaching-learning (didactical) activities, which draws on recent studies of scientific practice. We present and analyse the framework, which includes three categories: namely, Cosmos-Evidence-Ideas (CEI). We also apply this framework in order to model a posteriori the didactical activities included in three successive teaching-learning sequences in the field of fluids, developed gradually by the same researchers over several years under evolving dominant approaches to science teaching and learning (transmission, discovery, constructivist). For each sequence we analyse the planned activities included in student and teacher documents in terms of the CEI model. We deduce the suggested links (or lack of them) between the three categories and discuss the opportunities that students would have during science teaching to link in each sequence the world of theories with real things.