Enterprises develop procedures to address focuses in any case. However, procedures result often in sub-optimal solutions for any specific focus. As a consequence, each actor develops his own practice to address a focus in a given context, focus and its context being particular and specific. The modeling of practices is not an easy task because there are as many practices as contexts of occurrence. This paper proposes a way to deal practically with practices. Based on our definition of context, we present a context-based representation formalism for modeling task accomplishment by users called contextual graphs and its interest for the tasks of incremental acquisition, learning and explanation. Contextual graphs are discussed on a modeling in information retrieval.