drawing dfd

8/18/2019 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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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



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!

%



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



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

/



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

)



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



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

& .


& . / . &

: p d a t e , e m b e r ; i l e

& . / .

- e i n s t a t e

& . /


& . ) . &

: 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 ! 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/ . &


/ . . &

: 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

) . &


) . . &

: 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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DFD for


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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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#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

drawing dfd

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