LEVEL 1 DFD
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LEVEL 1 DFD
A level 1 dfd depicts the main functional areas of
the system under investigation. It is derived with
reference to the context diagram.

Level 1 DFDs are based on the context level DFD


All data flows entering or leaving a parent process
(process in context level) must also be shown as
entering or leaving the set of child processes (subprocesses in level 1)
Sub-processes for Level 1 DFDs


Provide a more detailed description of the system
Derived from the data flows going in and out of the
system.
LEVEL 1 DFD: SAMPLE SUB-PROCESSES
(BASED ON INCOMING DATA FLOWS)
Context Level Data Flow
New Customer
Information
Sends
Application
Reference
Level 1 DFD SubProcess
1
Add New
Customer
2
Record
Application
3
Check
Reference
LEVEL 1 DFD: SAMPLE SUB-PROCESSES
(BASED ON OUTGOING DATA FLOWS)
Context Level Data Flow
Inventory
Reports
Status
Message
Level 1 DFD SubProcess
4
Produce
Reports
5
Issue Status
Message
FOR EXAMPLE: HOW TO IDENTIFY SUBPROCESSES IN LEVEL 1?
Context Level DFD: Stock Control System
FOR EXAMPLE: HOW TO IDENTIFY SUBPROCESSES IN LEVEL 1?
Entity
In
Out Data Flow labelled in
context level
Production
Planning

Production Plan
Supplier

Delivery Note
Design

Bill of Materials
Factory

Stock Withdrawal note
Purchasing

Supplier Details Update
Form
Purchasing

Delivery Note Update
Purchasing

Material Requirements
List
Note:
Information
from the
Context
Level
Diagram
FOR EXAMPLE: HOW TO IDENTIFY SUBPROCESSES IN LEVEL 1?
Data Flow
labelled in
context level
Sub-Process
Production Plan
Update Production Plan
Delivery Note
Maintain Stock Card (inventory)
Bill of Materials
Maintain Stock Card (inventory)
Stock Withdrawal
note
Maintain Stock Card (inventory)
Supplier Details
Update Form
Update Supplier Form
Delivery Note
Update
Produce Reports
Material
Requirements List
Prepare material requirements list
Note:
Creating
subprocesses
to manage
data flows
from
context
level DFD
FOR EXAMPLE: HOW TO IDENTIFY SUBPROCESSES IN LEVEL 1?
Entity
Data Flow labelled in
context level
Sub-Process
Production
Planning
Production Plan
Update Production
Plan
Supplier
Delivery Note
Maintain Stock Card
(inventory)
Design
Bill of Materials
Maintain Stock Card
(inventory)
Factory
Stock Withdrawal note
Maintain Stock Card
(inventory)
Purchasing
Supplier Details Update
Form
Update Supplier
Form
Purchasing
Delivery Note Update
Produce Reports
Purchasing
Material Requirements
List
Prepare material
requirements list
IN
OUT
FOR EXAMPLE: HOW TO IDENTIFY SUBPROCESSES IN LEVEL 1?
Context Level DFD: Stock Control System
LEVEL 1 DFD: STOCK CONTROL SYSTEM
1
a.
Production
Planning
Production Plan
Update
Production
Plan
2
d.
Factory
Stock
Withdrawal
notice
Maintain Stock
Card
(inventory)
3
e.
Design
b.
Supplier
Delivery Note
Update
Supplier Form
Supplier Details
Update Form
c.
Purchasing
Material
Requirements
List
4
5
Produce
Reports
Prepare
Material
requirements
list
LEVEL 1 DFD: STOCK CONTROL SYSTEM

What next?
Ensure that there is a
flow of data
throughout the system
i.e: No breaks in between
sub-processes

LEVEL 1 DFD: STOCK CONTROL SYSTEM
1
a.
Production
Planning
Production Plan
Update
Production
Plan
No consistent flow of
data throughout the
system
Break
2
d.
Factory
Stock
Withdrawal
notice
b.
Supplier
Delivery Note
Maintain Stock
Card
(inventory)
Break
3
Update
Supplier Form
e.
Design
Break
Supplier Details
Update Form
c.
Purchasing
Material
Requirements
List
4
5
Produce
Reports
Break
Prepare
Material
requirements
list
LEVEL 1 DFD: STOCK CONTROL SYSTEM

Introduce new data flows between ‘breaks’
Data flows can flow between sub-processes providing
they do not produce a gray hole.
 Gray hole: The inputs to a process is not sufficient to
produce output flows
 Example of Gray hole:

Direct Debit
1
Data
Pay a bill
2
Generate a
bank
statement
Data from paying a bill is
insufficient to generate a bank
statement
Bank Statement
LEVEL 1 DFD: STOCK CONTROL SYSTEM

Introduce new data flows between ‘breaks’
continued..

Introduce data stores as these can reduce grey holes
from occurring
Direct Debit
1
2
Pay a bill
Generate a
bank
statement
Updated Account Balance
Data
Debit Account
D1 Bank Account
Bank Statement
Account
Balance
3
Update
Account
Balance
LEVEL 1 DFD: STOCK CONTROL
SYSTEM

Introduce new data flows between ‘breaks’
continued..

Look at each sub-process

Each sub process must have at least one input and one
output flow
To overcome a ‘BLACK HOLE’
• Introduce a data flow as an output
to the sub-process
BLACK HOLE
1
Generate a bank
statement
Bank Statement
Updated Account
Balance Data
LEVEL 1 DFD: STOCK CONTROL SYSTEM
1
a.
Production
Planning
Production Plan
Black hole
Update
Production
Plan
Black hole
2
d.
Factory
Stock
Withdrawal
notice
Maintain Stock
Card
(inventory)
3
e.
Design
b.
Supplier
Delivery Note
Update
Supplier Form
Supplier Details
Update Form
c.
Purchasing
Material
Requirements
List
Black hole
4
5
Produce
Reports
Prepare
Material
requirements
list
LEVEL 1 DFD: STOCK CONTROL
SYSTEM

Introduce new data flows between ‘breaks’
continued..

Look at each sub-process

Each sub process must have at least one input and one
output flow
To overcome a ‘Miracle’
• Introduce a data flow as an input
to the sub-process
Miracle
1
Generate a bank
statement
Bank Statement
Updated Account
Balance Data
LEVEL 1 DFD: STOCK CONTROL SYSTEM
1
a.
Production
Planning
Production Plan
Update
Production
Plan
2
d.
Factory
Stock
Withdrawal
notice
Maintain Stock
Card
(inventory)
3
e.
Design
b.
Supplier
Delivery Note
Update
Supplier Form
Supplier Details
Update Form
c.
Purchasing
Material
Requirements
List
4
5
Prepare
Material
requirements
list
Produce
Reports
Miracle
LEVEL 1 DFD: STOCK CONTROL SYSTEM
1
a.
Production
Planning
Production Plan
2
d.
Factory
Stock
Withdrawal
notice
b.
Supplier
Delivery Note
Maintain Stock
Card
(inventory)
3
e.
Design
‘As it stands’
Update
Production
Plan
Update
Supplier Form
Supplier Details
Update Form
c.
Purchasing
Material
Requirements
List
4
5
Produce
Reports
Prepare
Material
requirements
list
Level 1 DFD: Stock Control System
1
a.
Production
Planning
Production Plan
Planned Stock
Requirements
Update
Production
Plan
2
d.
Factory
Stock Withdrawal notice
Maintain Stock
Card
(inventory)
Delivery Note
D1 Stock Card
b.
Supplier
3
e.
Design
Update
Supplier Form
Supplier Details
Update Form
4
Material
Requirements
List
Delivery Note Update
Produce
Reports
c.
Purchasing
Request List
5
Prepare
Material
requirements
list
EXAMPLE


The management at ABC Burgers wishes to perform
systems analysis in order to improve its ordering
systems. The restaurant currently has a
computerized ordering system whereby customers
order food online. When customers place orders on
the Web site, the system sends the food order to the
Kitchen and issues a receipt to the customer. The
system also produces various reports, such as
management reports for the restaurant manager.
Construct a context level dfd and a level 1 dfd for
the above narrative.
SOLUTION: CONTEXT LEVEL

Assumption(s):
When the kitchen has completed the food order it
issues an update status to the system.
 The system then notifies the customer that the food
is ready for collection.

CONTEXT LEVEL DFD: ABC FOOD
ORDERING SYSTEM
0
Customer Order
a.
Customer
Receipt
Notification that food is ready
Food
Ordering
System
Management
Reports
c.
Restaurant
Manager
Food Order
Status
b.
Kitchen
LEVEL 1 DFD

Assumptions
Management reports are based on goods sold and inventory
 Two digital data stores exists

Goods Sold File
 Inventory File

Data Flows from
Context Level DFD
Associated Sub-Processes
Customer Order
Receive and transform Customer Food Order
Food Order
Receive and transform Customer Food Order
Receipt
Receive and transform Customer Food Order
Status
Checks Status
Notification that food
is ready
Issues Status
Management Reports
Produce Reports
LEVEL
‘As it stands’
1 DFD: ABC FOOD ORDERING SYSTEM
LEVEL
1 DFD: ABC FOOD ORDERING SYSTEM
In order to close this
break we must
introduce more
processes/data
flows/data stores to
ensure that reports
can be produced
Break
‘Miracle’
LEVEL
1 DFD: ABC FOOD ORDERING
SYSTEM
Additional Data Flows/ data stores and subprocesses to ensure reports could be produced