W3C XML Schemas on top

Tighten interpretation W3C XML Schemas are designed to enhance interoperability by creating a much tighter set of constraints on information than is possible with DTDs. Standards-builders can specify the fine print and expect computers to enforce it.
Add information XML Schemas add information to documents. Like DTDs, XML Schema provides attribute defaulting, though it doesn't provide entities. XML Schema also provides a lot more information about structure and data typing.
Typing, typing, typing Practically everything in W3C XML Schema is built around notions of strong typing for information. Where XML 1.0 is like Perl or VB, with variant types, XML Schema is much more demanding - like Java or C++.