W3C XML Schema takes an Object-Oriented Approach to XML

So... the W3C organized a committee, which built from Microsoft's XML Data Reduced (XDR) work, Commerce One's Schemas for Object-oriented XML (SOX), Data Description Markup Language (DDML), and Document Content Description (DCD). SOX and XDR seem like the plainly dominant influences.
Object-like type system Just like OOP, W3C XML Schema includes a hierarchical type system, using inheritance, pointers to other objects, and notions that data carries with it both a name (the element or object type name) and a more fundamental type (from the hierarchy).
Extension Like most OOP, W3C XML Schema provides for the addition of extra information to subtypes.
Restriction Like some OOP, W3C XML Schema provides for the creation of types which contain less information than their parent types.