UML Use Case/Sequence Diagram Creation

1
votes

I have to create a use case and sequence diagram for one of my assignments. Here is the description:

Consider the following description of the automated gas pump system.

An automated gas pump allows customers to use credit cards, debit cards and cash to purchase gas. When not in use the pump displays information about daily specials and sales. To use the pump, customers indicate the payment method. If cash is selected the customer waits until salesclerk activates the pump. If a credit card or debit card is used, customers swipe their card through a reader connected to the pump. In the case of a debit card a pin number is entered. The credit/debit card is validated by communication with a credit company computer and the pump is activated. The customer then selects the gas type, removes the "pump nozzle" from the pump and purchases gas by pumping the gas. The customer ends the transaction by replacing the "pump nozzle" back into the pump. If a credit/debit card was used the customer’s account is charged with the cost of fuel taken, the customer can select to print receipt and the transaction ends. If a cash payment is required, the pump remains idle until the salesclerk receives the customer's payment and resets the pump to an idle state. Daily station managers update pricing information for each grade of gas. Also, at the end of each day credit card transactions are sent to the credit card companies for payment.

For the Use Case Diagram I feel like it is right, just looking for feedback really.

UML Images:

Use Case Diagram

Sequence Diagram

For the Sequence Diagram the scenario is: "Purchase gas with a Credit Card"

I feel like i'm missing a GasPump controller entity or is it fine with just having how it is now? Also is the vehicle really necessary?

1
umluse-casesequence-diagram

1 Answers

3
votes

For use case diagram

  1. "Payment", "Gas type", "End of day summary" are not proper names for use cases. "Update price information" is.
  2. All of "include" are actually "extend" (if I understand the actual meaning of use cases properly). Since they are optional.
  3. Scenarios like "Payment", "End transaction" look like they are independent. This is not true, they are included in "Purchase gas". (I believe 'end transaction' is merely a step there and better be renamed to something reflecting the real action, like "Replace nozzle".)
  4. "Credit card companies computer" is not a good name for the actor. Use cases are technology-neutral and actor is a role, not set enumeration. Just "Credit card company".
  5. "Validate card" scenario is missing. I'd include it and "Activate pump" in a scenario like "Prove solvency".
  6. There is no need to have separate scenarios for debit and credit cards since it does not affect anything in the use case.
  7. Scenarios like "Calculate total amount" usually hide a lot of surprises and business rules, better to have it.

I feel like i'm missing a GasPump controller entity or is it fine with just having how it is now?

It depends on the level which you want to depict. In your case it seems to be user-goal level and you don't need a controller.

Also is the vehicle really necessary?

Only if it actually does something, i.e. if it is an actor.