This paper describes a multidisciplinary approach to the modelling of the mixed reality systems domain. Such modelling, useful for structuring such a recent interaction domain, and to facilitate design and evaluation from both software engineering and ergonomics perspectives, is based on the combination of two approaches: the ASUR notation and an ergonomic recommendations-based model. Both approaches are presented as well as the results of their combination. The resulting model, an extension of the ASUR notation, is described as well as its limits and perspectives.