cs451 - lecture 6 1 cs451 topic 6: dfd tutorial yugi lee stb #555 (816) 235-5932 leeyu@umkc.edu...
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CS451 - Lecture 61
CS451Topic 6: DFD Tutorial
Yugi Lee
STB #555(816) 235-5932
leeyu@umkc.edu
www.sice.umkc.edu/~leeyu
2CS451 - Lecture 6
The Data Flow Model
Every computer-based system is an Every computer-based system is an information transform ....information transform ....
computercomputerbasedbased
systemsysteminputinput outputoutput
3CS451 - Lecture 6
Data Flow Modeling Notation
external entityexternal entity
processprocess
data flowdata flow
data storedata store
4CS451 - Lecture 6
External Entity: A producer or consumer of data
•Data must always originate somewhere and must always Data must always originate somewhere and must always be sent to something e.g., be sent to something e.g., a person, a device, a sensor, a person, a device, a sensor, computer-based systemcomputer-based system
Process: A data transformer Process: A data transformer (changes input to output)(changes input to output)
•Data must always be processed in some way to achieve Data must always be processed in some way to achieve system function e.g., system function e.g., compute taxes, determine area, compute taxes, determine area, format report, display graph format report, display graph
External Entity & Process
5CS451 - Lecture 6
Data Flow
Data flows through a system, beginningData flows through a system, beginningas input and be transformed into output.as input and be transformed into output.
computecomputetriangle triangle
areaarea
basebase
heightheight
areaarea
6CS451 - Lecture 6
Data Stores
Data is often stored for later use.Data is often stored for later use.
look-uplook-upsensorsensor
datadata
sensor #sensor #
report requiredreport required
sensor #, type, sensor #, type, location, agelocation, age
sensor datasensor data
sensor numbersensor number
type, type, location, agelocation, age
7CS451 - Lecture 6
Constructing a DFD—I
• review ERD to isolate data objects and grammatical parse to determine “operations)
• determine external entities (producers and consumers of data
• create a level 0 DFD
useruserprocessing processing
requestrequest
videovideosourcesource NTSCNTSC
video signalvideo signal
digitaldigitalvideovideo
processorprocessor
requestedrequestedvideovideosignalsignal
monitormonitor
8CS451 - Lecture 6
Constructing a DFD—II
• write a narrative describing the transform
• parse to determine next level transforms
• “balance” the flow to maintain data flow continuity
• develop a level 1 DFD– use a 1:5 (approx.) expansion ratio
9CS451 - Lecture 6
The Data Flow Hierarchy
PPaa bbxx yy
p1p1p2p2
p3p3p4p4 55
aa
bb
cc
ddee
ff
gg
level 0level 0
level 1level 1
10CS451 - Lecture 6
Data Flow Diagrams (DFDs)
• Analysis tool
• System modeling
• Excellent documentation tool
• Data flow, aka, business process
• Provide a way to see the pattern– Systems Thinking– Systems View– Systems Approach
11CS451 - Lecture 6
Data Flow Diagrams (DFDs)
• Advantages for systems view, working with users:(1) External Entity - source and
destination ofdata
(2) Process
(3) Data Store
(4) Data Flow
12CS451 - Lecture 6
Data Flow Diagrams (DFDs)
• Simple rule:– left to right, top to bottom, basically (like English)– Show all processes– data flows must start or end in a process– beware of black holes - every process and data store
must produce data– no “magic processes” - must enter all needed data to
get data out
13CS451 - Lecture 6
DFD Example
Bebop Records is a mail-order company that distributes CDs and tapes at discount price to record-club members. When an order processing clerk receives an order form, he or she verifies that the sender is a club member by checking the Member file. If the sender is not a member, the clerk returns the order along with a membership application form. If the customer is a member, the clerk verifies the order item data by checking the Item file. Then the clerk enters the order data and saves it to the Daily Orders file. The clerk also prints an invoice and shipping list for each order, which are forwarded to Order Fulfillment.
14CS451 - Lecture 6
DFD Example: Step 1
FIRST SENTENCE:
Bebop Records is a mail-order company that distributes CDs and tapes at discount price to record-club members.
RESULT: initial title
Bebop Records
15CS451 - Lecture 6
DFD Example: Step 2
SECOND SENTENCE:
When an order processing clerk receives an order form, he or she verifies that the sender is a club member by checking the Member file.
RESULT:
Bebop Records Order Processing
EE-1
R e c o rd C lu bM e m b e r
1
Verify m em bers tatus
O R Clerk
EE-2
C u s t o m e r(n o n -m e m b e r)
D -1 M e m b e r M a s t e ro rd e r m e m b e rd a t a
16CS451 - Lecture 6
DFD Example: Step 2 (cont)
SECOND SENTENCE:
When an order processing clerk receives an order form, he or she verifies that the sender is a club member by checking the Member file.
RULES FOLLOWED:
• left to right, top to bottom
• data flows start or end in a process
17CS451 - Lecture 6
DFD Example: Step 3
THIRD SENTENCE:
If the sender is not a member, the clerk returns the order along with a membership application form.
RESULT:
Bebop Records Order Processing
EE-1
R e c o rd C lu bM e m b e r
1
Verify m em bers tatus
O R Clerk
EE-2
C u s t o m e r(n o n -m e m b e r)
D -1 M e m b e r M a s t e ro rd e r m e m b e rd a t a
n o n -m e m b e r o rd e ra n d a p p lic a t io n fo rm
18CS451 - Lecture 6
DFD Example: Step 3 (cont)
THIRD SENTENCE:
If the sender is not a member, the clerk returns the order along with a membership application form.
RULES FOLLOWED:
• shows all processes without conditions
19CS451 - Lecture 6
DFD Example: Step 4
FOURTH SENTENCE:
If the customer is a member, the clerk verifies the order item data by checking the Item file.
RESULT:
Bebop Records Order
Processing
EE-1
R e c o rd C lu bM e m b e r
1
Verify m em bers tatus
O R Clerk
EE-2
C u s t o m e r(n o n -m e m b e r)
D -1 M e m b e r M a s t e ro rd e r m e m b e rd a t a
n o n -m e m b e r o rd e ra n d a p p lic a t io n fo rm
2
Verify orderitem data
O R Clerk
m e m b e ro rd e r
D -2 It e m M a s t e rit e md a t a
20CS451 - Lecture 6
DFD Example: Step 5
FIFTH SENTENCE:
Then the clerk enters
the order data and saves
it to the Daily Orders file.
RESULT:
EE-1
R e c o rd C lu bM e m b e r
1
Verify m em bers tatus
O R Clerk
EE-2
C u s t o m e r(n o n -m e m b e r)
D -1 M e m b e r M a s t e ro rd e r m e m b e rd a t a
n o n -m e m b e r o rd e ra n d a p p lic a t io n fo rm
2
Verify orderitem data
O R Clerk
m e m b e ro rd e r
D -2 It e m M a s t e rit e md a t a
3
Enter orderin to D aily
O rders
O R Clerk
v e rifie dm e m b e r
o rd e r
D -3 D a ily O rd e rs D e t a ilo rd e r
21CS451 - Lecture 6
DFD Example: Step 5 (cont)
FIFTH SENTENCE:
Then the clerk enters the order data and saves it to the Daily Orders file.
RULES FOLLOWED:
• left to right, top to bottom
• data flows start or end in a process
22CS451 - Lecture 6
DFD Example: Step 6
SIXTH SENTENCE:
The clerk also prints
an invoice and shipping
list for each order, which
are forwarded to
Order Fulfillment.
EE-1
R e c o rd C lu bM e m b e r
1
Verify m em bers tatus
O R Clerk
EE-2
C u s t o m e r(n o n -m e m b e r)
D -1 M e m b e r M a s t e ro rd e r m e m b e rd a t a
n o n -m e m b e r o rd e ra n d a p p lic a t io n fo rm
2
Verify orderitem data
O R Clerk
m e m b e ro rd e r
D -2 It e m M a s t e rit e md a t a
3
Enter orderin to D aily
O rders
O R Clerk
v e rifie dm e m b e r
o rd e r
D -3 D a ily O rd e rs D e t a ilo rd e r
4
P rin t invoic eand
s hipping lis t
O R Clerk
o rd e rd a t a
EE-3
O rd e rF u lfillm e n t
in v o ic e a n ds h ip p in g lis t
23CS451 - Lecture 6
DFD Example: Step 6 (cont)
SIXTH SENTENCE:
The clerk also prints an invoice and shipping list for each order, which are forwarded to Order Fulfillment.
RULES FOLLOWED:
• left to right, top to bottom
• data flows start or end in a process
• shows all processes without conditions
• beware of black holes - every process and data store must produce data
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