Okay, I'm confused, is COD WW2's Nazi Zombies a separate Campaign with a story or will it be round based like zombies actually is

They made it sound like it's actually a story instead of it being round based. I don't know :|

what I'm trying to say is that it seems like it'll be a campaign mode about zombies instead of being round based. This makes me wonder if Zombies could possibly just be a one walk through type mode in this game kind of like campaign/Nightmare mode was