  The infrastructure upon which the functioning of society depends is composed
of complex ecosystems of systems. Consequently, we must reason about the
properties of such ecosystems, which requires that we construct models of them.
There are very many approaches to systems modelling, typically building on
complex structural and dynamic frameworks. Our purpose here is to explore a
modelling framework based on minimal assumptions, starting from a primitive
notion of behaviour, and to show that such an approach allows the recovery of
the key ideas, including a generalized CAP theorem, required for effective
modelling of and reasoning about ecosystems of systems. We establish a logic of
behaviours and use it to express local reasoning principles for the
compositional structure of systems.
