I've been thinking about this lately. Specifically, I see a connection between systems theory and graph theory. My intuition tells me that all relationships between systems can be expressed as graphs.
Can anyone confirm this? I'm not very familiar with either field, so I may be asking a basic question.
You would have to be more precise in describing what you mean by "all relationships between systems". A simple graph (meaning vertices and edges with no additional information) can encode the notions of a system and the existence of relationships between two systems, but without more structure you can't day much more. But this is already useful. If you have a big system you're trying to understand, a good first step is to draw a graph of the major components with edges indicating a dependency.
Systems interact through inputs and outputs, right? I mean, one system's output can be another system's input and even the second system's output can be the first one's input.
I guess my question was if there's something that can't be described or modelled with graphs.
As I said, my intuition is fuzzy, because I don't know much graph theory.
Can anyone confirm this? I'm not very familiar with either field, so I may be asking a basic question.