Use Case Diagram show a system from user's point of view. A Use Case Diagram models the interaction of actors with systems.
Here is a sample Use Case Diagram.

Some notes on the sample Use Case Diagram.
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Use Case "Take Order" can «include» sub-tasks such as Use Case "Serve Water".
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If the Extensions Points of Use Case "Prepare Order" apply, then Use Case "Prepare Order" can «extend» to Use Case "Restock".
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Generally Use Case "Deliver Order" can be substituted for Use Case "Serve Order" in particular situations.
2007-10-29 23:48:22Z