Re: [xml-dev] Is XML Schema a constraint language or a specification language?

Is an XML Schema a constraint language? An XML Schema states constraints that must be satisfied by instances for them to be "valid". Determining if an instance is valid is a constraint satisfaction problem.

Or, is an XML Schema a specification language? An XML Schema is a specification that informs instance document authors how to construct instances. Determining if an instance is valid is a matter of checking that the instance adheres to the specification.