To address the development of complex systems, the definition of novel models that capture their nature and provide developers with abstractions and technologies to both imagine and implement effective solutions is needed. Promising models are those based on Multi Agent Systems, since they naturally capture the concept of independent entities interacting in an environment.

This paper presents a model and discusses its social interaction mechanisms to support multi agent systems. The model, called Reaction Diffusion Machine (RDM), addresses the definition of environments hosting situated agents that may interact and move. Peculiarities of RDM are the inclusion of the topology of the space as a primitive aspect, and the definition of a interaction protocol that is based on the concept of distance among agents. The discussion on mechanisms addresses the issues to develop a framework that implements the model.