xml-dev - DTDs, W3 XML Schema, RELAX, or Schematron?

[Linda van den Brink <lvdbrink@baan.nl>]

Hi all, 

I've been wondering for a while about the use of DTDs, W3C XML Schema,
RELAX, and Schematron. Specifically about which of these to use in which
situation. So far, I only have experience with DTDs, and have only read
about the others (on this list, among other places). 

My impressions are as follows (sorry in advance for my vague notions): 
- DTDs: good for defining and validating human-written documents, especially
in structures where elements and PCDATA mix.
- W3C XML Schema: good for validating documents written and used by
computers (data exchange etc), especially for database-like structures.
- RELAX: positions itself in between DTDs and Schema, and can be used as
interim solution when you want to move from DTDs to Schema and don't want to
wait for Schema to become a recommendation. I'm not sure what specific
advantages/disadvantages RELAX has and what kinds of structures would fit
well with RELAX. 
- Schematron: good for validating content rules rather than structure rules.
E.g. elements with an enumerated list of allowed values. I think Schematron
could best be used in addition to DTDs?

What do others think about this? Am I right in thinking that DTDs, Schema,
RELAX, and Schematron each have their pros and cons that make them the best
choice in a certain situation? 

Or will DTDs become obsolete and will W3C XML Schema, RELAX, or Schematron
replace them? 

Wondering,
Linda van den Brink