I've used such a tool at university but I've now found out it's a subscription service. You could get graphs of papers that were cited and could use it to find

I've used such a tool at university but I've now found out it's a subscription service. You could get graphs of papers that were cited and could use it to find papers that were roots of a certain discipline. Though it wasn't as advanced a graph analysis as you propose it was pretty helpful. And you're right about journals sitting on that citation data. The service I used was http://en.wikipedia.org/wiki/Web_of_Science http://en.wikipedia.org/wiki/Web_of_Science