I think a "labeled port graph" is the suitable abstraction here. Graph nodes assert a number ports each with a label, composition is expressed as edges between

I think a "labeled port graph" is the suitable abstraction here. Graph nodes assert a number ports each with a label, composition is expressed as edges between ports. Optionally, ports may assert a type allowing only like-type edges to be valid. Ports may also assert a direction requiring outgoing to connect only to incoming. A nice feature of this concept (as also described in the article) is that a composition of a number of nodes can be recast to a single node which asserts the ports that have as yet not been connected.