Data flow diagram (Level 1): data flows

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Quick Questions

Shade in the A or B circle for each question.

1. A Level 1 DFD shows an arrow going straight from the entity 'Student' to the data store 'Orders'. Is this allowed?

A No, the flow must pass through a process

B Yes, entities can send data directly to stores

2. Which flow is valid in a Level 1 DFD?

A Process 'Check login' to data store 'Users'

B Data store 'Users' to entity 'Student'

3. What should every data flow arrow in a DFD have?

A A label naming the action, such as 'Process payment'

B A label naming the data that moves, such as 'order details'

4. Which label is best for a data flow arrow?

A booking request

B Validate booking

5. A Level 0 context diagram has the flows 'login details' in and 'welcome message' out. The Level 1 DFD should show:

A New external flows that were not on the Level 0 diagram

B The same flows entering and leaving the system from the same entities

Match the Pairs

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

Left column		Right column
1Customer --(order details)--> 1.0 Process Order		ACustomer --> 1.0 Record Order --(order record)--> Orders store
22.0 Check Stock --(stock level)--> Inventory store		BThe arrow has no label. It should name the data flowing, such as (order details).
3Data must never move straight between an external entity and a data store; a process must be in between		CA labelled data flow from a process into a data store, saving the stock level
4A Level 1 DFD is balanced with the Level 0 context diagram when the same inputs and outputs cross the system boundary		DLevel 0: Student --(enrolment form)--> System \| Level 1: Student --(enrolment form)--> 1.0 Enrol Student
5Customer --(payment)--> Sales store		EA flow goes directly from an entity to a data store. A process is missing, so the flow must be redirected through a process such as 3.0 Process Payment.
6Customer --> 1.0 Process Order		FA labelled data flow carrying order details from an external entity into a process

Definitions

data flow

Fill in the Blanks

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

Entity -> _______ -> Data Store

Every flow must start or end at a _______

Level 1 inputs and outputs must _______ with Level 0

D1 Orders __ 2.0 Print Invoice

Each data flow needs a _____ naming the data

Spot the Error

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

Question 1

A [Member] --form--> D1 List

B P1 Join --record--> D1 List

C D1 List --record--> P2 Check

D P2 Check --receipt--> [Member]

Question 2

A [Shopper] --order--> P1 Sell

B P1 Sell --> D1 Sales

C P1 Sell --receipt--> [Shopper]

Question 3

A [Student] --leave--> P1 Log

B P1 Log --entry--> D1 Late

C D1 Late --list--> P2 Sum

D D1 Late --report--> [Teacher]

Question 4

A L0 in: payment from [Customer]

B [Customer] --order--> P1 Take

C P1 Take --order--> D1 Orders

Question 5

A [Guest] --booking--> P1 Reserve

B P1 Reserve --room--> D1 Rooms

C D1 Rooms --free--> D2 Guests

D P2 Offer --options--> [Guest]

Answer Key

Data flow diagram (Level 1): data flows

Section A: Quick Questions

A — No, the flow must pass through a process

A — Process 'Check login' to data store 'Users'

B — A label naming the data that moves, such as 'order details'

A — booking request

B — The same flows entering and leaving the system from the same entities

Section B: Match the Pairs

Customer --(order details)--> 1.0 Process Order → A labelled data flow carrying order details from an external entity into a process

2.0 Check Stock --(stock level)--> Inventory store → A labelled data flow from a process into a data store, saving the stock level

Data must never move straight between an external entity and a data store; a process must be in between → Customer --> 1.0 Record Order --(order record)--> Orders store

A Level 1 DFD is balanced with the Level 0 context diagram when the same inputs and outputs cross the system boundary → Level 0: Student --(enrolment form)--> System | Level 1: Student --(enrolment form)--> 1.0 Enrol Student

Customer --(payment)--> Sales store → A flow goes directly from an entity to a data store. A process is missing, so the flow must be redirected through a process such as 3.0 Process Payment.

Customer --> 1.0 Process Order → The arrow has no label. It should name the data flowing, such as (order details).

Section C: Definitions

data flow — A labelled arrow showing data moving between entities, processes and data stores in a Level 1 DFD. Every flow must start or end at a process, so no entity-to-store flows.

Section D: Fill in the Blanks

Entity -> Process -> Data Store

Every flow must start or end at a process

Level 1 inputs and outputs must balance
 with Level 0

D1 Orders -> 2.0 Print Invoice

Each data flow needs a label naming the data

Section E: Spot the Error

A — A flow cannot go straight from an entity to a data store. Every flow must start or end at a process. It should be [Member] --form--> P1 Join, and the process then writes to D1 List.

B — Every data flow arrow needs a label that names the data being moved. It should be P1 Sell --sale--> D1 Sales.

D — A data store cannot send data directly to an entity. Data must pass through a process first. It should be P2 Sum --report--> [Teacher].

A — The Level 1 DFD must balance with Level 0. Level 1 shows an order flowing in from the Customer, so Level 0 must show the same flow, not payment.

C — A flow cannot go from one data store to another. Every flow must start or end at a process. It should be D1 Rooms --free--> P2 Offer.