UML relation between usecases (extend/include)

Question

I do not understand well following topic since it is a bit ambiguous from what I read:

• Inlcude is like a reference to next part, the usecase i

Answer 1

Here's an explanation from the following topic: UML Use Case Diagrams: Reference at http://msdn.microsoft.com/en-us/library/dd409427%28VS.100%29.aspx

Include: An including use case calls or invokes the included one. Inclusion is used to show how a use case breaks into smaller steps. The included use case is at the arrowhead end.

Extend: An extending use case adds goals and steps to the extended use case. The extensions operate only under certain conditions. The extended use case is at the arrowhead end.

Include and Extend relationships on a use case diagram http://i.msdn.microsoft.com/Dd409427.UML_UCOvStructure(en-us,VS.100).png