The paper introduces a mixed-method approach, based on the combination of an analytic technique of business process modelling and ethnographic research typically used in interpretive studies. Ontological and epistemological foundations are derived from the "subtle realism" approach. The study methodology offers an alternative to the ontological dichotomy of positivist and non-positivist frameworks and allows the researcher to apply methods of interpretive research without abandoning the commitment to arrive at a plausible account of objective reality. The mixed-method approach has the potential of bridging the gap between the formal context-insensitive language used by systems analysts with the informal, textual representation of socially situated data. Selected results of the case study of modelling the patient care process in the neurosciences ward of a public hospital in Melbourne, Australia, are presented to illustrate how ontological and epistemological assumptions have shaped the study from the stage of data collection to results interpretation and model design.