Defining the purpose of a system is non-trivial as, by definition, it arises from the relation with its environment. In this paper, we analyze relevant state of the art in the areas of General Systems Theory, Enterprise Engineering, Value Modeling, Enterprise Architecture and Business Modeling. Their main shortcoming essentially resides in lack of flexibly dealing with relativity of enterprise frontier definition. To address this issue, our research is focused on modeling different perspectives of enterprises as systems, namely construction, function and contribution. The approach presented in this paper involves 1) distinguishing the three mentioned perspectives and 2) articulating the concepts of each perspective so that an end-to-end, integrated, model is provided. To this end, we propose a conceptual framework that supports recursive contribution definition, by design. Specifying the value in a contribution perspective allows improved specification of the rationale behind value network establishment and system/subsystem bonding. We can now specify how each component of a system S contributes (provides value) not only to the purpose of S but to other purposes present in the value chains S participates in.