Naming our defense

I am a little confused about the names that have been given to the formations that our defense has been in. Looking at how we line up, the names of positions on our depth chart, and some of the posts on the blog/board I have some of this figured out but some of the information contradicts and that's what I want to get sorted out. Our depth chart shows a DE (Brandon Graham), a NT (Mike Martin), a DT (Ryan Van Bergen), a SLB (Stevie Brown), a MLB (Obi Ezeh), a WLB (Jonas Mouton), and an OLB (Craig Roh). This would indicate a 3-4 base, but I have been seeing it described as 4-3. Am I right in thinking this should be called a 3-4 or is there a reason for the OLB to count as a down lineman as well? Alright, so for this question I am assuming that the answer is that I am missing something and Craig Roh is actually a lineman. Stevie Brown was lining up at the edge most of the game and I have seen this as described as the 4-3 under, but wouldn't that be 4-3 over? I thought that the under indicated that the linebackers were favoring the weak side, but SB is on the strong side... Also, it seems that if Craig Roh should be considered a lineman while standing at the edge, Stevie Brown should be considered a lineman as well, which would really put us in more of a 5-2. Anyway, thanks in advance.