How to constrain set of attributes in xsd

Question

All Please suggest me how to restrict in xsd schema the following:

<root>
  <node action="action1" parameter="1" />
</root>

I need to require attribute "parameter" only if attribute "action" is defined.

Thanks,

Answer 1

W3C Schema doesn't have the ability to express conditionally required attributes.

Schematron is a great tool for validating that documents adhere to custom validation scenarios in which content is conditionally required.

You could define those attributes as optional in your schema, and then use Schematron to validate it against those conditional rules.