DTD Author Question

Hello all,

I am currently developing a "Subset" - "Variation"  of Docbook 4.4. I am 
declaring approximately 180 new elements, 50 new classes, and around 35 new 
entities. For 
this DTD, I will be utilizing a few of the current content elements/class 
from DB such as:
- title.content
- para.class
- orderedlist

I will include almost all the general entities.

Most elements/class/mix will be excluded though. What is the proper way to set 
the FPI for this instance? With such limited use of current DB elements, 
would this be a variation or subset or ??????

Thanks.
Thomas