Hospital information systems have to support quality improvement objectives. The requirements of the system have to meet users' needs in relation to both the quality (efficacy, conformity, safety) and the monitoring of all health care activities (traceability). Information analysts need complementary methods to conceptualize clinical information systems that provide actors with immediate individual benefits and guide collective behavioral changes. A methodology is proposed to elicit users' needs using a process-oriented analysis, and it is applied to the field of blood transfusion. We defined a process data model, the main components of which are: activities, resources, constrains, guidelines and indicators. Although some aspects of activity, such as "where", "what else", and "why" are poorly represented by the data model alone, this method of requirement elicitation fits the dynamic of data input for the process to be traced. A hierarchical representation of hospital activities has to be found for this approach to be generalised within the organisation, for the processes to be interrelated, and for their characteristics to be assessed.