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To the best of my knowledge there isn't an easy way to display an XML schema definition (XSD) with the help of UML diagrams currently. However, such visualization seems more intuitive when trying to grasp complex relations of types than the schema design view. This especially holds true when you want to create a printout for larger schemas. The URL in this feature request points to a set of Eclipse plugins that permit the import of XSD files into UML diagrams. I would like to see something similar (or better) also for NetBeans, maybe also connected to code generation (Castor is able to generate Java source code out of XSD, see http://www.castor.org/).