Data flow diagram of a system

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Quick Questions

Shade in the A or B circle for each question.

1. What does a data flow diagram show?

A How data moves between users, processes, storage and external services

B The exact lines of code a program runs, in order

2. Which one is an external entity in a login system?

A The step that checks the password

B The user who types in a username and password

3. Which one is a data store in a data-saving system?

A A student typing in a form

B A user accounts database

4. Which label is best for an arrow from the user to the login process?

A Username and password

B Data

5. What is a process in a data flow diagram?

A A step that takes in data and changes it or makes a decision, like 'Check login'

B A place where data is stored permanently, like a database

Match the Pairs

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

Left column		Right column
1[Student] --> (Check login)		A[Student] -- username + password --> (Check login)
2=Accounts DB=		BA data store, which is where the system keeps data such as user accounts so it can be used later
3Every arrow in a data flow diagram must be labelled with the data it carries		CAn entity (the student) sends data into a process, shown as an arrow from the entity to the process
4A process that saves data sends it to a data store, and the arrow shows what is saved		D(Save score) -- new score --> =Scores DB=
5[Student] --> =Accounts DB=		EThe flow has no arrowhead, so the direction of the data is unclear. Every data flow needs an arrow showing which way the data moves.
6(Check login) -- login result -- [Student]		FAn entity is sending data straight into a data store with no process in between and no label on the arrow. Data should pass through a process, and the flow should be labelled.

Definitions

data flow diagram

Fill in the Blanks

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

______: Student process: Log in store: Accounts

entity: Student _______: Log in store: Accounts

entity: Student process: Save score _____: Scores

Student -> Log in : login details Log in __ Accounts : look up user

Student -> Log in : login details Log in -> Accounts : look up user ________ -> Log in : user record

Spot the Error

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

Question 1

A [User] -> (Login): username

B (Login) -> {Accounts}: check

C {Accounts} -> [User]: record

D (Login) -> [User]: result

Question 2

A [Student] -> (Save): file

B (Save) -> {Files}

C (Save) -> [Student]: receipt

Question 3

A [Shopper] -> (Order): details

B [Shopper] -> {Orders}: order

C (Order) -> [Shopper]: receipt

Question 4

A [Member] -> (Sign up): details

B (Sign up) -> {Members}: save

C (Sign up) -> [Mailer]: address

D [Mailer] -> [Member]: welcome

Question 5

A [Teacher] -> (Marks): grades

B (Marks) -> {Results}: save

C (Report) -> {Results}: marks

D (Report) -> [Teacher]: report

Answer Key

Data flow diagram of a system

Section A: Quick Questions

A — How data moves between users, processes, storage and external services

B — The user who types in a username and password

B — A user accounts database

A — Username and password

A — A step that takes in data and changes it or makes a decision, like 'Check login'

Section B: Match the Pairs

[Student] --> (Check login) → An entity (the student) sends data into a process, shown as an arrow from the entity to the process

=Accounts DB= → A data store, which is where the system keeps data such as user accounts so it can be used later

Every arrow in a data flow diagram must be labelled with the data it carries → [Student] -- username + password --> (Check login)

A process that saves data sends it to a data store, and the arrow shows what is saved → (Save score) -- new score --> =Scores DB=

[Student] --> =Accounts DB= → An entity is sending data straight into a data store with no process in between and no label on the arrow. Data should pass through a process, and the flow should be labelled.

(Check login) -- login result -- [Student] → The flow has no arrowhead, so the direction of the data is unclear. Every data flow needs an arrow showing which way the data moves.

Section C: Definitions

data flow diagram — A diagram that shows how data moves between users, processes, data stores and external services in a system, using labelled arrows for each flow.

Section D: Fill in the Blanks

entity: Student
process: Log in
store: Accounts

entity: Student
process: Log in
store: Accounts

entity: Student
process: Save score
store: Scores

Student -> Log in : login details
Log in -> Accounts : look up user

Student -> Log in : login details
Log in -> Accounts : look up user
Accounts -> Log in : user record

Section E: Spot the Error

C — Data cannot flow straight from a data store to an entity. It must pass through a process. The line should be {Accounts} -> (Login): record.

B — Every data flow arrow needs a label that names the data moving along it. This line should be (Save) -> {Files}: file data.

B — An entity cannot write straight into a data store. A process must handle the data first. The line should be (Order) -> {Orders}: save.

D — Data should not flow directly between two external entities, because the system is not involved. The welcome message should come from the (Sign up) process.

C — The arrow is the wrong way round. The report process needs to read marks from the store, so it should be {Results} -> (Report): marks.