← VCE Software Development U3O2

Data flow diagram (Level 1): data flows

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.

Part of: VCE Software Development - U3O2 - Analysis and Design — Module 45, QCE Digital Solutions Unit 2 — Data-Driven Problems and Solution Requirements — Module 89, QCE Digital Solutions Unit 3 — Interactions Between Users, Data and Digital Systems — Module 27, QCE Digital Solutions Unit 4 — Digital Methods for Exchanging Data — Module 130, QCE Digital Solutions Unit 4 — Complex Digital Data Exchange Problems and Solution Requirements — Module 92

Understanding Data flow diagram (Level 1): data flows in VCE Software Development U3O2

What it does: The process 1.0 sits between the entity and the store, so every flow starts or ends at a process. The enrolment form flow appears in both diagrams with the same label and entity, so the diagrams balance. Flow labels name the data travelling along the arrow (a noun phrase). Actions like 'Process payment' belong inside process bubbles. Balancing means the Level 1 DFD must have the same inputs and outputs to and from external entities as the Level 0 context diagram. Extra detail is added inside the system only. Data is saved into a store by a process and retrieved from it by a process. Entities never connect straight to a store.

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

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This module's key terms are also in a printable crossword (Modules 42–51) and word search (Modules 26–51).

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Learning
Duo
A Level 1 DFD shows an arrow going straight from the entity 'Student' to the data store 'Orders'. Is this allowed?
No, the flow must pass through a processYes, entities can send data directly to stores
Matches
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.
Applying
Meanings
Term
data flow
Meaning
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.
Practice
Member -> 1.0 Borrow Book : book request
Testing
Gaps
Entity -> -> Data Store
Check Answer
Spots
1[Member] --form--> D1 List
2P1 Join --record--> D1 List

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Quick Questions

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
Every data flow in a Level 1 DFD must start or end at a process. An entity cannot send data straight to a data store, so a process such as 'Record order' must sit between them.
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'
A flow between a process and a store is valid. A store cannot send data directly to an entity, because the data has to pass through a process such as 'Display profile'.
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' ✓
Flow labels name the data travelling along the arrow (a noun phrase). Actions like 'Process payment' belong inside process bubbles.
4. Which label is best for a data flow arrow?
A. booking request ✓
B. Validate booking
A flow label names the data. 'Validate booking' is a verb phrase, which suits a process, not a flow.
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 ✓
Balancing means the Level 1 DFD must have the same inputs and outputs to and from external entities as the Level 0 context diagram. Extra detail is added inside the system only.

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).

Key Term

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.

Fill in the Blanks

1. Entity -> Process -> Data Store
Hint: Type the Level 1 element that must sit between an entity and a data store.
2. Every flow must start or end at a process
Hint: Type the DFD element that every flow must touch at one end.
3. Level 1 inputs and outputs must balance with Level 0
Hint: Type the word for making the flows match the parent context diagram.
4. D1 Orders -> 2.0 Print Invoice
Hint: Type the arrow symbol that shows data moving from the store into the process.
5. Each data flow needs a label naming the data
Hint: Type the word for the text written on a flow arrow to say what data moves.

Spot the 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]
Line 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.
Question 2
A [Shopper] --order--> P1 Sell
B P1 Sell --> D1 Sales
C P1 Sell --receipt--> [Shopper]
Line B — Every data flow arrow needs a label that names the data being moved. It should be P1 Sell --sale--> D1 Sales.
Question 3
A [Student] --leave--> P1 Log
B P1 Log --entry--> D1 Late
C D1 Late --list--> P2 Sum
D D1 Late --report--> [Teacher]
Line 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].
Question 4
A L0 in: payment from [Customer]
B [Customer] --order--> P1 Take
C P1 Take --order--> D1 Orders
Line 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.
Question 5
A [Guest] --booking--> P1 Reserve
B P1 Reserve --room--> D1 Rooms
C D1 Rooms --free--> D2 Guests
D P2 Offer --options--> [Guest]
Line 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.

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