That example is kind of...disjointed I guess.
A better one would be in mimicry of Winamp's Media Library. It's broken into panes. As you update one pane, the next pane in line alters as well.
My setup is like this: 1. Genre -> 2. Category -> 3. Album -> 4. MP3s.
So in Genre I click Video Game. This updates Category to only categories available to the Genre "Video Game". (Meaning basically "Genre = Video Game" and "Category = <this>"
In Category, I can then select "Castlevania". Now pane 3 is updated again. The albums shown all have this in common -> "Genre = Video Game" and "Category = Castlevania".
I can select the album -> Lament of Innocence OST, to update the bottom pane, which shows my mp3s, in this case, now only the mp3s of the Lament of Innocent OST.
It may seem complicated to some, but to me it's the most logical and easy way to sort and search my mp3s, and I'd really love similar functionality for searching and sorting through my ebooks.