Extension is used when modeling a profile to extend UML (or SysML).
Extension is a kind of Association. One end of the Extension is an ordinary Property and the other end is an ExtensionEnd. The former ties the Extension to a (meta)Class, while the latter (ExtensionEnd) ties the Extension to a Stereotype that extends the Class.
To model an Extension, perform these steps:
1 Create a UML2-5-1 Extension definition – either by creating the definition through the Explorer tree or drawing such a symbol on a diagram.
2 Create a Stereotype definition.
3 Draw an Association Node to Stereotype as ExtensionEnd from the UML Extension definition to the Stereotype.
4 Draw an Association Node to Class as Property from the Extension definition to all other associated Classifiers.
5 When the relationship is drawn, you can specify to have the name of the UML Extension placed outside the symbol – right-mouse click on the UML Extension symbol, select Format > Symbol Format > Text Position, and toggle on the choice Place Name Outside.
6 Optionally specify that the extension is Required in the A_ownedEnd_extension property of the ExtensionEnd definition.
Relates
The Association End to Stereotype as ExtensionEnd relationship can be drawn like this:
