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   Interface is defined as a specialization of the general Interface, adding an association to a protocol state machine. 
   • 
               Interface (from Communications	   ) on page 461 
               (merge increment) 
   Description 
   Since an interface specifies conformance characteristics, it does not own detailed behavior specifications. Instead, interfaces
               may own a protocol state machine that specifies event sequences and pre/post conditions for the operations and receptions
               described by the interface. 
   Attributes 
   No additional attributes 
   Associations 
   •	protocol: ProtocolStateMachine [0..1] References a protocol state machine specifying the legal sequences of the invocation
               of the behavioral features described in the interface. 
   Semantics 
   Interfaces	    can specify behavioral constraints on the features using a protocol state machine. A classifier realizing an interface
               must comply with the protocol state machine owned by the interface. 
   Changes from previous UML 
   Interfaces	    can own a protocol state machine.