Data Flow Diagram Example
1.
Draw a context level DFD for the following order system.
Precision Tools
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.
First:
Identify the central process: in this case, it is the Order System.
Second.
Identify External Entities (EE) and Data Flows (DF):
Precision Tools sells a line of high-quality woodworking tools. When customers
[EE] place orders [DF] on the company’s Web site, the system checks to see if
the items are in stock, issues a status message [DF] to the customer, and
generates a shipping order [DF] to the warehouse [EE], which fills the order.
When the order is shipped, the customer is billed [DF]. The system also produces
various reports [DF].
Note: Precision Tools, or more specifically the Order website, is the system being
modelled, not an External Entity.
A sample context diagram might look like this:
IN - STOC K
R EQU EST
OR D ER
W A R EH O U SE
C U STOMER
PAYMEN T
0
STATU S
MESSAGE
SH IPPIN G OR D ER
OR D ER
SYSTEM
SH IPPIN G C ON FIR MATION
IN VOIC E
IN VEN TOR Y
R EPOR TS
A C C OU N TIN G
D EPA R TMEN T
2.
Draw a diagram 0 DFD for the order system.
So, how do we determine what sub-processes there are? Data flows can give us some
clues: for example, a Status Message cannot materialize from nowhere, it needs to be
issued by a process. Similarly, Reports must be produced and Orders generated.
What Data Stores to include will need a little thought.
A sample diagram 0 might look like this:
SH IPPIN G C O N FIR MATION
1
IN -STOC K R EQU EST
OR D ER
C H EC K
STATU S
STATU S
D ATA
STATU S
MESSAGE
C U STOMER
W AR EH OU SE
OR D ER D ATA
D1
PEN D IN G
OR D ER S
2
IN VO IC E
OR D ER
D ATA
PAYMEN T
ISSU E
MESSAGES
5
3
MAN AGE
AC C O U N TS
R EC EIVABL E
GEN ER ATE
SH IPPIN G
OR D ER
AC C O U N TIN G
D ATA
D3
SH IPPIN G
OR D ER
AC C O U N TS
R EC EIVABL E
D ATA
AC C O U N TS
R EC EIVABL E D ATA
4
OR D ER D ATA
PR OD U C E
R EPOR TS
IN VEN TO R Y
R EPOR TS
AC C O U N TIN G
D EPAR TMEN T