DocBook schema/DocBook XSL customization for teaching purposes

Hi, list members.

I'm planning to extend docbook specification and docbook xsl-stylesheets for courseware 
material authoring: class schedules, course programs and notes, self assesments, 
projection slides, etc.

There is some questions (that needs your expirience with docbook) to be answered:

Is there any consideration to extend docbook by adding new problem orinented elements, 
such as  <course />, <module />, <topic />, <lab />, <exercise />... Actually, I just want 
to reuse major docbook elements (%divcomponent.mix) within new document structure ...
or should I just "annotate" existing elements <book />, <article />, <section /> by using 
role="..." attribute?

Any thoughts about advantages and disadvantages resulted from these different approaches?

Dimitry.