Extend relationship (UML Use-case)

The extend relationship, $⟨⟨\text{extend}⟩⟩$, is where the behaviour of one use case (extending use case) may be integrated in the behaviour of another use case (base use case) but does not have to. Both use cases may be executed independently of each other.

• $A$ decides if $B$ is executed.
• Extension points define at which point the behaviour is integrated.
• Conditions define under which circumstances the behaviour is integrated.
• Multiple extension points may be specified.
• Extension points are written directly on the use case.

digraph {
	layout=neato
	splines=true
 
	actor [shape=star label=""]
	actor->A,B [arrowhead=none]
	B->A [label=" «extend»"]
}