In brief, the XML Schema: Note: The current version of XSD 1.1 (september 2012) became a approved W3C specification in April 2012.
A DTD can be declared inside an XML document (i.e., inline), or referenced as an external file.
An inline DTD is wrapped in a DOCTYPE declaration, and has the following syntax: 3.
XML Schema Definition (XSD) XML Schema developed by W3C via a recommendation in May 2001, is a description language to define the structure and content type of an XML document.
It overcomes the limitation of DTD and meant to replace DTD for the checking of XML document validity.