Dfd continued..
Context and Level 1
Exercise For context level dfd
Precision Tools sells a line of high-quality
woodworking tools. When customers place orders
on the company’s Web site, the system checks to
see if the items are in stock, issues a status
message to the customer, and generates a shipping
order to the warehouse, which fills the order. When
the order is shipped, the customer is billed. The
system also produces various reports, such as
inventory reports for Accounting.
• Draw a context diagram for the order system
•Document any assumptions you may have made
about the system.
Assumptions for context level dfd
• State assumptions
– Company’s website is the ordering system
– When the order is shipped a shipping confirmation is
sent by the warehouse to the system
– An update is provided to the system after every instock request
– Customer pays for woodworking tools orders
– After every inventory report is sent to Accounting an
acknowledge of delivery is sent back to the system
Context level components
Identify Process
 Order System
Identify entities
 a. Customer
 b. Warehouse
 c. Accounting
Identify data flows
•
•
•
•
•
•
•
•
•
•
Order
In-Stock Request
Status Message
Shipping Order
Invoice
Shipping
Confirmation
Payment
Inventory Reports
Acknowledgement
Stock Update
Context level DFD: Precision Tools
Key notes for context level dfd
• The Context Level DFD attempt to show the
workings of the entire system at a glance.
• It is the top level DFD and the first to be drawn
• This level consists of only one process.
• Depicts the interaction between the system
and external entities.
• This level does not contain data stores
Level 1 dfds
LEVEL 1 DFD
When the context level is expanded into a Level
1 DFD, all the connections which flow into and
out of process 0 (process in context level)
needs to be retained.
DFDs are expanded or decomposed into levels.
 Separating each process into sub processes
 Uncovers more and more detail

Level 1 DFDs
• At level 1 you begin to look in more detail at the
different processes within an organisation.
• Gives overview of full system
• Identifies major processes and data flows between
them
• Identifies data stores that are used by the major
processes
• Boundary of level 1 is the context diagram
• The level 1 diagram shows the main functional areas of
the system under investigation.
• A level 1 DFD notates each of the main sub-processes
that together form the complete system.
Context level  Level 1
a.
Nurse
Patient Medical
Details
Patient Status
Healthcare System
b.
Doctor
Healthcare System
1
a.
Nurse
Patient Medical
Details
Update Patient
medical Details
Status Data
2
Patient Status
Checks Status
b.
Doctor
How to identify sub-processes in level
1?
• All data going into the system must be
received by a process within the system
• All data going out of the system must be
generated by a process within the system.
• Based on the data flows from the context level
generate your sub-processes
Step 1: Identify Sub-Processes
from Context Level
Tip: In = Receive
Out = Generate
1. Process Results
2. Generate Report
3. Send Notification
4. Receive Updated Results
5. Produce Final
Result Report
Step 2: Draw Identified Sub-Processes
Step 3: Bound with Context Level
Data Flows
Step 4: Add in extra data flows and
check flow and Logic
Step 5: Restructure and Change if
Necessary
Another Example: How to identify subprocesses in level 1?
Context Level DFD: Stock Control System
For Example: How to identify subprocesses in level 1?
• Data Flows in context level
– Production Plan
– Delivery Note
– Bill of Materials
– Stock Withdrawal note
– Supplier Details Update Form
– Delivery Note Update
– Material Requirements List
For Example: How to identify subprocesses in level 1?
• Data Flows in context level
In
Out
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
Production Plan
Update
Production Plan
D1 Stock Card
Planned Stock
Requirements
Stock
RequirementDetail
d.
Factory
Level 1 DFD:
Stock Control System
1
Stock Withdrawal notice
b.
Supplier
Delivery Note
2
Notify
Supplier
a.
Production
Planning
Maintain Stock Card
(inventory)
3
Update Supplier
Form
Prepare Material
requirements list
Material
Requirements List
Supplier Details
Update Form
5
Bill Of Material
Stock Data
e.
Design
4
Delivery Note Update
Request List
Produce Reports
c.
Purchasing
Steps in Constructing Level 1 DFD
1. Take the single process on the Context Level DFD and
break it up into its constituent sub-processes.
2. Pick out data stores from the text. However, these
are not always stated explicitly in the narrative. These
are used as a repository of information for the system
– and should be named in plural. Please note that data
stores are not included on the context level DFD.
Include them on DFDs which have been exploded
from the context level DFD.
3. Construct the Level 1. Make sure the entities, data
stores and processes are named and labelled.
Precision tools exercise continued..
Level 1
Precision Tools sells a line of high-quality
woodworking tools. When customers place orders
on the company’s Web site, the system checks to
see if the items are in stock, issues a status
message to the customer, and generates a shipping
order to the warehouse, which fills the order. When
the order is shipped, the customer is billed. The
system also produces various reports, such as
inventory reports for Accounting.
• Draw a Level 1 DFD for the order system
•Document any assumptions you may have made
about the system.
Assumptions for level 1 dfd
• State assumptions
– Company’s website is the ordering system
– When the order is shipped a shipping confirmation is sent
by the warehouse to the system
– An update is provided to the system after every in-stock
request
– Customer pays for woodworking tools orders and records
are kept (accounts receivable)
– After every inventory report is sent to Accounting an
acknowledge of delivery is sent back to the system
– There are 2 digital data stores
• D1 Pending Orders
• D2 Accounts Receivable
Level 1

Data Flows

• Entities
– Customer
– Warehouse
– Accounting
• Sub-Processes
–
–
–
–
–
1. Check Status
2. Issue Status Messages
3.Generate Shipping Order
4.Manage Accounts Receivable
5. Produce Reports
• Data Stores
– D1 Pending Orders
– D2 Accounts Receivable















Order
In-Stock Request
Order Data
Status Data
Status Message
Shipping Order
Order Pending Data
Invoice
Shipping Confirmation
Payment
Accounting Data
Accounts Receivable Data
Order Data
Inventory Reports
Stock Update
Acknowledgement
LEVEL 1 DFD: PRECISION TOOLS
Level 1 DFDexercise
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
Food Ordering
System
Receipt
Notification that food is ready
Food Order
b.
Kitchen
Status
Management
Reports
c.
Restaurant
Manager
Level 1 DFD
• Assumptions
– Management reports are based on goods sold and
inventory
– Two digital data stores exists
• from
Goods
Sold Associated
File
Data Flows
Context
Sub-Processes
Level DFD• Inventory File
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 1 DFD: ABC food Ordering System
‘As it stands’
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