A Diagram Gate is a simple graphical way to indicate the point at which messages can be transmitted into and out of interaction fragments. A fragment might be required to receive or deliver a message; internally, an ordered message reflects this requirement, with a Gate indicated on the boundary of the fragment's frame. Any external messages 'synching' with this internal message must correspond appropriately. Gates can appear on Interaction diagrams (Sequence, Timing, Communication or Interaction Overview), interaction occurrences and combined fragments (to specify the expression).
- Sequence Diagram
- Timing Diagram
- Communication Diagram
- Interaction Overview Diagram
- Interaction Occurrence
- Combined Fragment
OMG UML Specification:
The OMG Unified Modeling Language specification, (v2.5.1, pp.575-576) states:
A Gate is a MessageEnd which is used on the boundary of an Interaction, or an InteractionUse, or a CombinedFragment to establish the concrete sender and receiver for every Message.
Gate instances, since they occur in a paired manner linking two Message instances, are also not themselves explicitly ordered. Gates are MessageEnds which provide a connection point between, either:
- a Message instance outside of an InteractionUse and a Message instance inside the used Interaction, or;
- a Message instance outside a CombinedFragment and a Message instance inside a InteractionOperand within the CombinedFragment.