Given the following state transition diagram. Which of the following series of state transitions contains an INVALID transition which may indicate a fault in the system design?

Question

Exhibit

Options

• ALogin Browse Basket Checkout Basket Checkout Pay Logout.
• BLogin Browse Basket Checkout Pay Logout.
• CLogin Browse Basket Checkout Basket Logout.
• DLogin Browse Basket Browse Basket Checkout Pay Logout.

• A
  8% (5)
• B
  2% (1)
• C
  85% (51)
• D
  5% (3)

Explanation

Option C is correct because it contains the invalid transition Basket → Logout. After returning from Checkout back to Basket, the sequence jumps directly to Logout - bypassing the required Checkout and Pay states. In a well-designed e-commerce state machine, Logout is only reachable after completing (or explicitly cancelling) the payment flow, not directly from the Basket.

Why the distractors are wrong:

• A is valid: it shows a user returning from Checkout to Basket (a common "edit cart" back-transition), then re-entering Checkout and completing payment before logging out.
• B is valid: it's the standard happy-path sequence with no deviations.
• D is valid: it shows a user returning from Basket to Browse to add more items - a normal browsing loop before proceeding to checkout.

Memory tip: Focus on the destination of each transition, not just whether backtracking occurs. Backtracking (Checkout → Basket, Basket → Browse) is usually allowed; the red flag is a shortcut that skips a mandatory state - here, going from Basket straight to Logout without ever reaching Pay.

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