I used to walk past the Harder House on SW 10th and Market every day, where I think the systems PhD program sits. They have these fascinating network diagrams stuck up in the windows, and I was always curious what they were...
Yep, that's the place... if it's the one I'm thinking of, then I think it's a diagram of a search through a set of potential models during a RA (Reconstructability Analysis) of 3 independent variables with 1 dependent variable.
It's Dr. Marty Zwick's favorite picture since he's the one who teaches DMM (Discrete Multivariate Modeling) which deals with RA. I haven't taken it yet, but he was at ISSS and gave a plenary on RA, as well as chaired a full day of RA related presentations.
Here is some more information, which also has the diagram I think you're referencing:
