[dataflow]

The most minimal example of it I can think of would be a little ridiculous, but it could look like this:

  interface Edge { }
  interface Graph {
    List<Edge> getRoots();  // Returns some ~minimal set of edges with connectivity to all the others
    List<Edge> getAdjacentEdges(Edge e, boolean tail);
  }

There's no way to directly refer to a vertex here at all (unlike with edges), and yet (since edges have identity) there's enough information to determine the graph structure!

[naasking]

What's an example of an algorithm that could use this sort of interface? All of the algorithms that immediately come to mind are more require more vertex information.