The governance of interaction is a critical issue in the engineering of agent systems. Research on coordination addresses this issue by providing a wide range of models, abstractions and technologies. It is often the case, however, that such a wide range of proposals could not easily find an unitary and coherent conceptual framework where all the different views and solutions can be understood and compared—and this is particularly true in the context of agent models and systems.
In this paper, we first discuss how all the many diverse approaches to agent coordination can be categorised in two main classes – the subjective and objective approaches – depending on whether they adopt the agent's or the engineer's viewpoint, respectively. We then claim that the two approaches have a deep and different impact on the way in which agent systems are modelled and built, and show two examples rooted in different models and technologies. Finally, we advocate that both approaches play a fundamental role in the engineering of agent systems, and that any methodology for the design and development of agent systems has to exploit both objective and subjective coordination models and technologies.