desktop-base-trinity

What is the difference between desktop-base (Debian's deb) and desktop-base-trinity (Trinity's deb). I did a Trinity install, over and above another DE, for a friend the other day so he could see what Trinity was and I noticed it wanted to remove desktop-base and install desktop-base-trinity instead. I didn't allow it to install desktop-base trinity and everything is working fine so I was wondering what is the need for it. Cheers. Michael.