The User Definition Types are used to build up the User Diagram Types. For example, if you created a Library Diagram, you will want to add definition types to support your modeling scenario.
To create a user definition type
1 Perform one of these actions:
•In the Explorer, right-click the Definitions group, and then select New Definition.
•Click Dictionary > New Definition.
2 Select User Definition Type, and then specify a name for it.