This week's book giveaway is in the Agile and Other Processes forum. We're giving away four copies of The Journey To Enterprise Agility and have Daryl Kulak & Hong Li on-line! See this thread for details.
XML schema allows two types of inheritance; extension and restriction.
Extension is easy to accomplish in, for instance Java, or some other OO language: Just add new fields to the subtype.
Restriction is slightly more complicated, since you cannot remove fields from a superclass in a subclass.
It is possible to override any getters and setters for a field to be removed and make them do nothing, but the field is still there.