How can I tag a movie in iTunes?

I have some movies in iTunes that are purchased from the iTunes Store. I have some movies in iTunes that are from my own collection.

I noticed that when I am browsing a list of them on my Apple TV, the ones I have purchased from the iTunes Store are nicely tagged with actors, directors, producers, even MPAA Rating. However, when I look at the info for the movie in iTunes, I don't see any of those tags. Is there any way to get those tags populated in movies from my own collection?