Cyber-physical systems have tightly interacting physical and computational parts
Model system behavior as the passing around and processing of signals (e.g. real numbers).
Interaction can be thought of as variable sharing
Physical coupling between train cars forces their velocity to be the same
Categorical treatment of co-design problem allowed us to evaluate composite feasibility relation from a diagram of simpler feasibility relations.
Likewise we can evaluate whether two different signal flow graphs specify the same composite system
(perhaps to validate that a system meets a given specification)
Symmetric monoidal preorders were a special class of symmetric monoidal category where morphisms are constrained to be simple (at most one between any pair of objects).
Signal flow diagrams can be modeled by props, which is a special class of symmetricf monoidal category where objects are constrained to be simple (all are generaated by the monoidal product of a single object).
In the former we have to label wires but not boxes. Vice-versa for props.