A Union Class is a Simple Type element that defines a collection of Simple Types. You can create it by dragging the Union icon from the XML Schema Toolbox and dropping it directly on a diagram.

Toolbox Icon

Access Drag icon onto diagram, or

Project Browser | Double-click on «XSDunion» stereotyped element, or

Diagram | right-click on «XSDunion» stereotyped element | Properties

Define Properties



See also


If you do not want to use the default name of the Union, overtype it with another name.

Member Types

Click on the button to display the 'XSD Union Members' dialog, and select built-in XSD datatypes and Simple Type elements to be members of the collection.

  • Choose - Instead of typing or selecting values in the 'Class Name' field, click on this button to display the 'Select Classifier' browser and locate and select a Simple Type element; click on the OK button to close the browser and immediately add the selected element to the 'Type Details' list
    This option is generally used to specify objects that are in the same Package as the Union element, but you can select objects in any other Package also
  • Add - Click on this button to add the data type or element specified in the 'Class Name' field to the 'Type Details' list
  • Accept classifier even if not in model - Select this checkbox to include elements or data types that have been named but that are not present in the same model Package as the Union element
  • Type Details - Review the list of selected elements or data types; if you intend to remove an object from the list, highlight it and click on the Delete Selected button
  • Delete Selected - Click on this button to remove the currently-selected Classifier from the 'Type Details' list
  • Close - Click on this button to close the 'XSD Union Members' dialog and to list the selected elements and data types in the 'Member Types' field

Simple Type


(Optional) Type any notes you need for this element.


Click on this button to save the attribute data entered and close the XSD union 'Properties' dialog.


Click on this button to discard the attribute data entered and close the XSD union 'Properties' dialog.


Click on this button to display this Help topic.


This button is displayed when you are editing existing «XSDunion» element information.

Click on the button to open the UML element 'Properties' dialog for the «XSDunion» element.



  • When you click on the Close button on the XSD union 'Properties' dialog, a Generalization connector is added to the diagram from the XSD Union element to each of the member elements on the same diagram; any elements not on the same diagram are listed in the top right corner of the XSD Union element
  • If the Member Types that are not on the same diagram as the Union element are not listed, select 'Tools | Options | Diagram | Behavior' and select the 'Show Hidden Parents' checkbox
  • A Union element:
         -  Cannot contain any child Classes
         -  Cannot contain any «XSDelement» or «XSDattribute» stereotyped UML attributes
         -  Cannot be the source of an Association connector
         -  Can be the target of an Association connector from a Complex Type element
         -  Can be the target of a Generalization connector from a Simple Type element

Learn more