Schema development for information design & authoring

Hello

With a more general modeling background in a number of other aspects,
I'm a newcomer to "formal" information design and data modeling.

I'm interested in learning more about the business merit and application
areas of schema development to the last. I could see that DTDs, and more
recently RELAX NG and Schematron, are being used for industry standard
XML-based authoring applications; but that's mostly a one-time per.

I'm wondering about the business case magnitude/significance of schema
development for purpose of information development & design,
documentation, and content management.

Is it relatively true that the prominent merit is in the area of
controlling data exchange for eCommerce and Web Services?

Thank you very much for any insight.

Regards.
Khaled