Regarding Use case Diagram

Hello All,
I am trying understand Use Case Diagrams.
Let us consider this simple use case diagram from Wikipedia

Here Patron (customer) is shown to have 3 cases

  1. Order Food
  2. Eat Food
  3. Pay for Food

My question is shouldn’t the diagram show dependency between 1) and 2) ? i.e. Shoudn’t the diagram show that the Eating Food can happen only after Ordering Food.

Please correct me if I am wrong.

Thanks a lot.

No. The timing or sequencing order in which use cases are invoked is not the primary concern of use case diagrams. That is better dealt with in a sequence diagram by modelling the steps (actor/system interactions) described in each use case.

A better way to deal with such dependencies is to use pre-conditions. A use case’s pre-conditions:
– Define the conditions the system ensures will be true before allowing the actor to initiate the use case.
– Are the same for all of the use case’s scenarios.
– Are not validated/checked by the use case itself (it assumes the pre-conditions are met).
– Usually correspond to the post-conditions of some other use case(s).

In your example:
– Use case Eat Food could have this pre-condition: The actor has received food.
– This would correspond to use case Order Food’s post-condition: The system has presented food to the actor.