Newbie: create named data items?

[Thomas Nichols <nx10mail@yahoo.co.uk>]

Hi,

I'm just starting to use DocBook XML in earnest, I'm trying to (ab?)use the 
DTD to store "meta" information about the text. Am I approaching this aright?

Problem: a <book> has <section>s for a number of minerals. For each, I have 
a Name, a "History" section, a "Geology" section, etc. I want to create a 
valid DocBook doc, so that I can publish the entire book, but I want to add 
markup to allow me to print, say, just Name and Geology sections. A 
different stylesheet might extract just Name and History sections.

I'm effectively trying to use the doc as generic and processable XML data, 
within the confines of DocBook. Is this a terrible approach? Would I be 
best writing in "uber-DocBook", my own markup which allows
<geology>p>blah...</p></geology>
and then transforming this into valid DocBook by either evaporating or 
excluding the spurious "geology" tags.

I'd like to get to the point where the user says "show me the Name, 
Abundance in Earth's Crust and History" and the appropriate sections will 
be emitted. What other approaches can anyone suggest? Any feedback would be 
very welcome.

Regards,
Thomas.