oXygen XML Schema Editor

Oxygen offers a side by side presentation of the schema source and diagram. The diagram is synchronized in real time with the source editor: selecting an element in the diagram highlights the corresponding element in the source editor, while moving the caret in the source editor changes the selection in the diagram view. The schema diagram renders all the XML Schema and Relax NG components and allows you to quickly navigate to the referred definitions of elements, attributes, types, groups, patterns, etc. Two types of visual diagram are available for a schema: the Full Model View and the Logical Model View.

http://www.oxygenxml.com/xml_schema_editor.html