Data flow diagram (Level 1): data stores and entities

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Quick Questions

Shade in the A or B circle for each question.

1. Which best describes a data store on a Level 1 DFD?

A A place inside the system where data is held, such as a file or database

B A person or organisation outside the system that sends data in

2. Which of these is an external entity on a Level 1 DFD?

A Customer who submits an order

B Orders database

3. Which data flow is NOT allowed on a Level 1 DFD?

A Customer (entity) straight to Orders (data store)

B Customer (entity) to Process Order (process)

4. Do data stores appear on the Level 0 context diagram?

A Yes, every data store must be drawn around the system

B No, the context diagram shows the system as one process with its entities only

5. The context diagram shows entities Student and Teacher. Which Level 1 DFD is consistent with it?

A Level 1 adds a new entity, Principal, that was not in the context diagram

B Level 1 shows Student and Teacher as the external entities

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1D1 \| Student records		AProcess 2.0 Check stock -> D2 Product file
2Parent (external entity)		BAn external entity that sits outside the system and sends data to it or receives data from it
3A Level 1 DFD must keep the same external entities as the context diagram		CContext diagram entities: Customer, Bank \| Level 1 entities: Customer, Bank
4Data in a store can only move to or from a process, never directly to an entity		DAn external entity is connected directly to a data store. Data must pass through a process first, such as 1.0 Record order.
5Customer -> D1 Orders file		EA data store on a Level 1 DFD, drawn as an open-ended rectangle with an ID and a name, showing where data is held
6Context diagram: Customer only \| Level 1: Customer, Supplier		FThe Level 1 DFD adds a Supplier entity that is not on the context diagram, so the two diagrams are inconsistent.

Definitions

Data store

Fill in the Blanks

Complete each line of code by filling in the missing parts.

__________: D1 Orders

______: Customer

Context entity: Customer Level 1 entity: ________

Entities sit _______ the system boundary

Store: D1 Orders Flow: 1.0 Process Order -> _________

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A Context entity: Student

B L1 entity: Teacher

C L1 store: D1 Student file

D Student -> 1.0 Enrol: form

Question 2

A Entity: Teacher

B Teacher -> 1.0

C 1.0 -> D1: mark record

D D1 -> 2.0: mark record

Question 3

A Entity: Parent

B Store D1: Payment file

C Parent -> D1: payment

D 1.0 -> D1: payment record

Question 4

A Process D1: Book catalogue

B Entity: Member

C Member -> 1.0: loan request

D 1.0 -> D1: loan record

Question 5

A Entity: Customer

B Store D1: Order file

C D1 -> Customer: order details

D 2.0 -> Customer: receipt

Answer Key

Data flow diagram (Level 1): data stores and entities

Section A: Quick Questions

A — A place inside the system where data is held, such as a file or database

A — Customer who submits an order

A — Customer (entity) straight to Orders (data store)

B — No, the context diagram shows the system as one process with its entities only

B — Level 1 shows Student and Teacher as the external entities

Section B: Match the Pairs

D1 | Student records → A data store on a Level 1 DFD, drawn as an open-ended rectangle with an ID and a name, showing where data is held

Parent (external entity) → An external entity that sits outside the system and sends data to it or receives data from it

A Level 1 DFD must keep the same external entities as the context diagram → Context diagram entities: Customer, Bank | Level 1 entities: Customer, Bank

Data in a store can only move to or from a process, never directly to an entity → Process 2.0 Check stock -> D2 Product file

Customer -> D1 Orders file → An external entity is connected directly to a data store. Data must pass through a process first, such as 1.0 Record order.

Context diagram: Customer only | Level 1: Customer, Supplier → The Level 1 DFD adds a Supplier entity that is not on the context diagram, so the two diagrams are inconsistent.

Section C: Definitions

Data store — On a Level 1 DFD, a data store is where data is held (e.g. a file or database). Entities sit outside the system and send or receive data. Both must match the context diagram.

Section D: Fill in the Blanks

Data store: D1 Orders

Entity: Customer

Context entity: Customer
Level 1 entity: Customer

Entities sit outside the system boundary

Store: D1 Orders
Flow: 1.0 Process Order -> D1 Orders

Section E: Spot the Error

B — The Level 1 DFD must match the context diagram. Teacher is not an entity on the context diagram, so it cannot appear here. It should be Student.

B — Every data flow between an entity and a process must be labelled with the data it carries. It should be Teacher -> 1.0: marks entered.

C — An external entity cannot send data straight to a data store. The data must go through a process first, so it should be Parent -> 1.0: payment.

A — D1 is a data store because it holds data (the book catalogue). It is not a process. It should be Store D1: Book catalogue.

C — A data store cannot send data directly to an external entity. A process must read the data from the store and send it on, so it should be D1 -> 2.0: order details.