Architecting and designing : UML 2.5 : Model Elements : Structured Classifiers : FunctionBehavior
  
FunctionBehavior
UML specifies several types of behaviors:
Activity
State Machine
Interaction
Opaque Behavior, which has subtype FunctionBehavior
A FunctionBehavior enables you to model external functions that take only inputs and produce outputs, and are not part of the modeled system.
Example
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See also
Class
Activity
AssociationClass
Interaction
OpaqueBehavior
State Machine
Stereotype
Device
ExecutionEnvironment
Collaboration
Component
Node
Protocol State Machine
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Structured Classifiers