Information about creating XML DTDs/Schemas

Dear all,

I know this is not exactly the right group for answering this question 
but I thought that many of you have experience with XML, so:

Does somebody of you knows links to good tutorials and/or books on 
learning how to create XML DTDs or Schemas? I want to create a DTD for 
Standard Operating Procedures of the company I'm working for, because I 
think Docbook is to complicated for this purpose, although I love to 
work with it, but I suspect that the learning curve is to high for most 
of our SOP authors.

Cheers
B.