Schema Justification
Description of document type’s structure should be in an XML document instead of written in special syntax (DTD).
Schema are in XML: easier to edit and process using standard XML DOM manipulation tools.
DTD notation doesn’t allow schema designers the power to impose strong data typing -- for example, the ability to say that a certain element type must always have a positive integer value, that it may not be empty, or that it must be one of a list of possible choices.