ISO Schematron

open schema language — constraint based, rather than grammar based
the feather duster that gets the corners the vacuum cleaner can’t reach
basically tests a set of conditions you write, and issues a message you write for each condition that fails
examples:
- do dates of birth precede dates of death?
- are there any <lb> elements that immediately follow a <pb>?
- are there any duplicate @xml:id values?
- does the @ref of <persName> really point to a <persion>?
can (and should) be incorporated directly into your ODD
can be used standalone, too, of course
relies on XPath

Schematron in ODD slide 02 of 39