[wcarss]

That makes me wonder if there are actually any cycles in paper citations. I can imagine this scenario:

A paper X has been updated to reference a response or later work Y, which itself referenced X from the start in such a way as to make the 'version' of X in the reference unknown. Citation-trawling software might bite hard on a loop like that :P

Anyway, I also wonder why having cycles makes PageRank useful and lacking them makes it less so -- you can still count inbound links and such with a DAG, and huge huge amounts of the content of the web would exist in DAG-equivalent subtrees, wouldn't they? I could have this pretty wrong, haven't looked at the paper in years and should go do so!

[Eridrus]

PageRank is overkill if you don't have cycles, since you can just trivially count the DAG.