Ask HN: Software to create and visualize social graphs for historical figures?

I'm looking for an app or website to create directed graphs that show who worked on a particular topic and who learned from whom. Vertices should show the names and edges the kind of relationship. For example: (Sokrates) --teacher-of--> (Platon) --teacher-of--> (Aristoteles) Musts: - Usable on my iPhone (app or responsive website) - Easy data entry - Automatic visualization of the resulting graph - Free text on the edges (to show the kind of relationship) Nice to haves: - Data export - Different styles for edges and vertices. - Longer-form annotations (e.g. a pointer to the source of an info) - Parallel edges (multigraph) I expect my graphs to contain only a few dozen nodes at maximum. Graphviz and a plain text editor feel too cumbersome for spontaneous use. Instaviz comes close, but doesn't seem to allow any text on the edges. Mental (by J.-Y. Vocisano) has no automatic layout. SocNetV, OntoWiki and RDF seem too complicated for my purpose.