This work presents amethod that aims at structuring the design process of interactive information systems (IIS). This method, which takes parts of its ground in the joint cognitive systems approach, formalizes the integration of usage data in the design process of IIS. Data are generated by using methods of activity analysis. The assumption is that for integrating usage data successfully, they must be represented in a formalism close to the development language, while maintaining the formalization language accessible to each domain specialist involved in the design process. The method can be split up into in five steps: (a) data collection of users' needs in different contexts, (b) representation of the collected data, (c) modeling of corresponding knowledge in an implementation formalism, (d) specification of the IIS, and (e) validation of the model by a functional specification aid tool. A functional specification design tool has been developed according to the presented approach, and has been applied to the design of a traveler information system.