While there are many useful models of agents and multi- agent systems, they are typically defined in an informal way and applied in an ad-hoc fashion. Consequently, multi-agent system designers have been unable to fully exploit these models commonalities and specialise or reuse them for specific problems. In order to fully exploit these models and facilitate their reuse we propose a formal approach based upon organ- isational concepts. The formal notation is the result of the composition of Object-Z and statecharts. The semantics of this multi-formalisms is defined by transition systems. This operational semantics enables valida- tion and verification of specifications. We present this approach through the specification of the satisfaction-altruism model which has been used to design situated multi-agent systems. We put the emphasis on the spec- ification of a mobile robot architecture based on the refinement of this model. The availability of such generic models is a fundamental basis for reuse. We also show how to analyse the specification by validation and verification.