Drawing DFD
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Page 1Data Flow Diagramming
Data Flow Diagram
(DFD)
Review
Learning Objective
This collection of slides will review the
techniqe of drawing data flow diagrams!
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Page "Data Flow Diagramming
#hat is a Data Flow Diagram$
% & data flow diagram (DFD) is a gra'hical
tool that allows sstem analsts (and sstem
sers) to de'ict the flow of data in aninformation sstem!
% The DFD is one of the methods that sstem
analsts se to collect information necessarto determine information sstem
reqirements!
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Page Data Flow Diagramming
#hat is a Data Flow Diagram$
% & Data Flow Diagram is intended to serve
as a commnication tool among
* sstems analsts
* end sers
* data base designers
* sstem 'rogrammers
* other members of the 'roject team
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Page +Data Flow Diagramming
#hat does a DFD loo, li,e$
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Page -Data Flow Diagramming
#h Draw Data Flow Diagrams$
% To clearl and concisel commnicate the flow of data
throgh a sstem!
% #h se a DFD and not jst te.t$ – “Since we previously had no way of showing a tangible model, we have had
to build the next best thing, which is to use English narrative to describe the
proposed system. Can you imagine spending five years’ salary on a custombuilt house on the basis of an exhaustive narrative description of how the
house will be built ... !f you use English to describe a complex system... the
result ta"es up so much space that it’s hard for the reader to grasp how the
parts fit together
#$ane and Sarson, Structured System %nalysis, &'()*
% DFD/s are easier to nderstand than te.t!
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Page 0Data Flow Diagramming
DFD mbols and Definitions
Data flow
External
Entity
Data store
Process
% Process 2 'erforms some action on
data3 sch as creates3 modifies3
stores3 delete3 etc! 4an be manal
or s''orted b com'ter!
% Data store 2 information that is,e't and accessed! 5a be in
'a'er file folder or a database!
% 6.ternal entit 2 is the origin or
destination of data! 6ntities aree.ternal to the sstem!
% Data flow 2 the flow of data into or
ot of a 'rocess3 datastore orentit
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Rles for Drawing DFD/s
& minimum of one data flow
in and one data flow ot of
a 'rocess
& datastore must beconnected to a 'rocess
(either in3 ot3 or both)
&n e.ternal entit must
be connected to a 'rocess(either in3 ot3 or both)
& single data flow must
onl flow one wa
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DFD9 4ommon 5ista,es
% Process has no data flowing
into it3 bt has data flowing
ot!
% Data store is hoo,ed to
e.ternal entit! This meanse.ternal entit can read and
write to or data file
withot aditing::
% The data flow goes in twodirections at once! Two or
more arrows shold be sed
to show the flow to and
from each 'rocess!
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DFD 6.am'le 1
% The
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DFD9 &dding Levels of Detail
% The highest level3 called the context diagram, is onl anoverview! 5ore detail is t'icall needed for sstemanalsts!
% #e add detail to a DFD b creating ?levels@! The first leveladded after the conte.t diagram is called level ?>@!
% 6ach new level brea,s a'art one 'rocess and ?decom'oses@the single 'rocess into a new3 more detailed DFD! &com'lete DFD can have man (' to 0 or 7) levelsde'ending on the com'le.it of sstem!
%
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DFD9 Ambering Levels
% Bn a DFD with man levels it/s eas to forget whichlevel o are on! That/s wh each level hasdifferent nmbering for the 'rocesses on thediagram! The Clevel/ corres'onds to the nmber of
decimal 'laces reqired to define a 'rocess in it!ere/s how it wor,s9
* 4onte.t Diagram Process labeled ?>@ * Level > Processes labeled 1!>3 "!>3 !>3 !
* Level 1 Processes labeled 1!13 1!"3 1!3 !
* Level " Processes labeled 1!113 1!1"3!!!
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To' (>) Process Level
+ r o a d w a y E n t e r t a i n m e n t S y s t e m
, e m b e r s h i p
&
- e n t a l
S a l e s
/
! n v e n t o r y
)
E m p l o y e e
0
! n 1 S t o r e S y s t e m
2
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Level 19 5embershi'
E n r o l
& . &
! s s u e 3 e w C a r d
& .
- e i n s t a t e
& . /
4 r a n s i e n t
& . )
, e m b e r s h i p
&
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Level 19 Rental(note this is the 'rimitive level for this series of 'rocesses)
- e n t . &
- e t u r n .
- e p o r t s . /
- e n t a l
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Level 19 ales
5 r o c e s s S a l e s
/ . &
5 r o c e s s - e t u r n s
/ .
S a l e s
/
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Level 19 Bnventor
6 r d e r ) . & - e c e i p t) . - e 7 e c t) . / 4 r a n s f e r ) . )
! n v e n t o r y
)
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Level 19 6m'loee
4 i m e - e p o r t i n g
0 . &
% d d 8 9 e l e t e
0 .
E m p l o y e e
0
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Level "9 5embershi'
! n p u t , e m b e r 9 a t a
& . & . &
% s s ig n , e m b e r 3 u m b e r
& . & .
: p d a t e , e m b e r ; i l e
& . & . /
E n r o l
& . &
! n p u t , e m b e r 3 u m b e r
& . . &
5 r in t C a r d
& . .
! s s u e 3 e w C a r d
& .
! n p u t , e m b e r 3 u m b e r
& . / . &
: p d a t e , e m b e r ; i l e
& . / .
- e i n s t a t e
& . /
! n p u t , e m b e r 3 u m b e r
& . ) . &
: p d a t e 4 r a n s i e n t - e n t a l ; i le
& . ) .
4 r a n s i e n t
& . )
, e m b e r s h i p
&
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Level "9 ales
! n p u t , e m b e r 3 u m b e r
/ . & . &
! n p u t ! t e m 9 a t a
/ . & .
: p d a t e S a l e s ; i l e
/ . & . /
5 r in t - e c e i p t
/ . & . )
5 r o c e s s S a l e s/ . &
! n p u t ! t e m 9 a t a
/ . . &
: p d a t e S a l e s ; i l e
/ . .
5 r in t - e c e i p t
/ . . /
5 r o c e s s - e t u r n s
/ .
S a l e s
/
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Level "9 Bnventor
! s s u e 5 u r c h a s e 6 r d e r
) . & . &
) . & .
6 r d e r
) . &
! n p u t ! t e m 9 a t a
) . . &
: p d a t e ! n v e n t o r y ; i l e
) . .
: p d a t e - e c e i p t s ; i le
) . . /
- e c e i p t
) .
! n p u t 6 r d e r ! t e m) . / . &
: p d a t e - e 7 e c t i o n - e p o r t ; i le) . / .
- e 7 e c t
) . /
! n p u t ! t e m 3 u m b e r
) . ) . &
: p d a t e ! n v e n t o r y ; i l e s
) . ) .
4 r a n s f e r
) . )
! n v e n t o r y
)
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Level "9 6m'loee
! n p u t E m p l o y e e 3 u m b e r
0 . & . &
! n p u t 4 i m e S h e e t 9 a t a
0 . & .
4 i m e - e p o r t i n g
0 . &
! n p u t E m p l o y e e 9 a t a
0 . .
% s s i g n E m p l o y e e 3 u m b e r
0 . . /
: p d a t e E m p l o y e e ; i l e0 . . )
% d d
0 . . &
! n p u t E m p l o y e e 3 u m b e r
0 . / . &
: p d a t e E m p l o y e e ; i l e
0 . / .
9 e l e t e
0 . /
% d d 8 9 e l e t e
0 .
E m p l o y e e0
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DFD Levels9 4onte.t Diagram
% First we can start to draw a generaloverview! This general overview is called a
?4onte.t Diagram@!
%& 4onte.t Diagram shows three things9 * all e.ternal entities
* a single 'rocess labeled ?>@that re'resents the
entire sstem (food ordering sstem)
* the major information flows between the
e.ternal entities and the sstem!
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Page "Data Flow Diagramming
DFD Levels9 4onte.t Diagram
% Bt wold be im'ossible to nderstand all of
the data flows3 and to identif all of the
Ce.ternal entities/ relating to orinformation sstem in one 'ass3 so we tend
to draw DFD/s incrementall!
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Page "+Data Flow Diagramming
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Page "-Data Flow Diagramming
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Page "0Data Flow Diagramming
DFD9 Logical vs Phsical
% Aote that the 4onte.t Diagram did NOT record themovement of merchandise3 bt rather the information
flow srronding the nderling bsiness 'rocesses! * & DFD that shows the movement of information is
called a ?logical@ DFD!
* & DFD that shows the movement of 'hsical stff(sch as merchandise) is called a ?physical@ DFD!
% The logical DFD is b far the most common t'e of
DFD and therefore we will focs on this in this class!
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Page "7Data Flow Diagramming
DFD for
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Page "8Data Flow Diagramming
4onte.t Level(note there are no storage elements at this level)
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Page ";Data Flow Diagramming
Level >
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Page >Data Flow Diagramming
DFD9 ome Final Aotes
% ow man 'rocesses on a diagram$ * rle of thmb is to have - 2 7 'rocesses3 if o need more3
create a new level!
% &re there conventions for naming objects$
* 'rocess names are verb 'hrases
* all others are non 'hrases
% ow man levels shold o go$
* Onl as man as o need to commnicate adeqatel!The ,e is efficient commnication!
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Page 1Data Flow Diagramming
#hat have we learned$
% #hat is a DFD and #h do we se DFD/s$
% #hat are the rles for drawing DFD$
% #hat is a 4onte.t Diagram$
% #hat is the difference between logical and
'hsical DFD$
% #hat is a Level > DFD$
% #hat is balancing and decom'osition$
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6'iloge
% The