Appropriation of technology is a process by which users complete the work of designers by making interactive systems functional within the frame of their situated activities. While existing theories and studies about appropriation are oriented toward psychological or organizational dimension of this process, we propose a model to describe appropriation process through evolutions of digital artifacts and information structures. A case study shows that this model helps to identify some operations carried out by user to transform digital material in regard of the appropriation process. These findings open perspectives to bridge scattered theoretical approach of appropriation around a low-level, artifact-oriented, and objective way of describing appropriation. It also could help design-for-appropriation by bringing more focus on technical aspect of interactive systems.