I would take out the word "syntactic." Databse schemata have much more
than syntactic constraints. Arguably, so do document schemata. Is IDREF
a syntactic constraint? Not according to my intuition.
Paul Prescod - http://itrc.uwaterloo.ca/~papresco
Three things never trust in: That's the vendor's final bill
The promises your boss makes, and the customer's good will
http://www.geezjan.org/humor/computers/threes.html