Document Structure Definition (DSD) is a newly announced schema language for XML documents produced as a result of collaborative research between AT&T and BRICS University in Denmark.

DSD is able to express conditional constraints, ordered and unordered content types and other features beyond the power of DTDs. It also provides a CSS style mechanism for inserting default elements and attributes, and as such is different from the W3C Schema language which is currently a Working Draft.

The DSD language is already fully implemented and is open source. More information is available from the DSD website.