Complex system design requires a multi-disciplinarily approach deploying a multiplicity of point of views. The OREA (Organization-Role-Entity-Aspect) model presented in this paper proposes a conceptual framework allowing to represent a complex system in different points of view and to integrate them in order to form a coherent system. Using an AgentGroup-Role (AGR) extension, OREA allows not only to represent a system from various points of view through the roles played by entities within organizations, but also to allow various entities to play a same role in various ways through the notion of aspects. Unlike most roles based models, OREA provides a clear distinction between (1) the external properties of an entity described by the roles and (2) the internal properties described by the aspects. The OREA model increases organization reuse and the adaptability of a system. OREA model have been implemented in Mimosa and used to implement a simulator for carbon dynamics analysis at village territory level.