Something to Chew On

Just a quick couple of questions tonight. I've got 350 pages to read for work this weekend, so I haven't had time (or energy) to come up with very much depth. But I was having a conversation earlier today that I thought I'd toss out to see what anyone else made of it.

If the full field of journalism is a set, how large is the subset of investigative journalism? What other subsets are there? In particular, how does this relate to political journalism?