The modeling tool allows for displaying the messages when leaving or entering a sequence diagram, interaction use, or combined fragment. The Gate is a connection point for representing a message from the outside to the current sequence diagram, interaction use, or combined fragment.

Gates can be used in three cases:

• For passing and returning arguments to InteractionUse, which calls some Interaction.
• For displaying “exceptions“ as messages that stops an interaction execution and leaves it.
• For “calling“ sequence blocks represented as CombinedFragments.

Gate has no notation. Gates are created as message ends when drawing messages to/from a diagram frame, an interaction use, or a combined fragment.

To create a formal gate, do one of the following

• Draw a call, send, create, or delete a message from the diagram frame.
• Draw a reply message to the diagram frame.
• Draw a call, send, create, or delete a message from the combined fragment (inside combined fragment).

To draw create an actual gate of the formal gate, do one of the following

• Draw a call, send, create, or delete a message to the interaction use, which refers to the diagram with the formal gates. The Select Formal Gate dialog opens.
• Draw a reply message from the interaction use, which refers to the diagram with the formal gates. The Select Formal Gate dialog opens. 
• Draw a call, send, create, or delete a message to the combined fragment (outside combined fragment). The Select Formal Gate dialog appears.

To select a formal gate for the actual gate

1. Do one of the following:
   
   • Draw a message.
   • From the message shortcut menu, choose Select Formal Gate.
2. In the open dialog, select one of the listed formal gates and click OK. An actual gate is created.