ITPEC IP October 2022 Question 95
When a guest arrives at a certain restaurant, their name is registered in a visitor list. When the guest is allocated a seat, both the guest list and seating availability are referenced. Which of the following is the most appropriate DFD to represent this series of actions?
Explanation
Reception writes to Guest list; Show to seat reads Guest list and Seating availability — the DFD in (d).
In a DFD, an arrow from a process into a data store means the process writes to it, and an arrow from a store into a process means the process reads it. The story gives three flows:
- •The guest's name is registered in the visitor list: Reception → Guest list
- •Seating refers to the guest list: Guest list → Show to seat
- •Seating refers to seating availability: Seating availability → Show to seat
Only (d) draws exactly these three.
Answer (d)
Why not others:
- •(a) — Reception reads the Guest list instead of registering in it, and Show to seat writes to Seating availability instead of referring to it
- •(b) — Reception writes to Seating availability, Show to seat sends data back to Reception, and nobody registers the guest in the Guest list
- •(c) — Reception registers the guest but also writes to Seating availability, and Show to seat reads neither store; it only receives a flow from Reception
Key rule: Read the arrow direction at every data store: into the store is registering or updating, out of the store is referring to it.
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