DATA FLOW DIAGRAMS

PRESENTATION BY –

SAYEEDA HAJIRA ARSHIYA FARTHEEN .A.

WHAT ARE DATA FLOW DIAGRAMS ????

DATA FLOW DIAGRAMS… Abbreviated as DFD Introduced by DE MARCO , GANE , and SARSON Most important tool used by system analysts Main merit of DFD is that it can provide an

overview of :-• what data system would process• what data transformations are done• what data are stored and which stored data is used• where the results flow The graphical representation of the system makes

it a good communication tool between a user and an analyst and also the analyst and a system designer

SYMBOLS USED IN DFDS :

Used to depict a process

Shows the direction of flow of data

Used to represent external entities

Represents data store

DESCRIBING A SYSTEM WITH A DFD :

Let us consider an example of a mess management system and describe it with the help of a data flow diagram (DFD)………….

MESS MANAGEMENT

SYSTEM

VENDORSSTUDENTS

MESSSECRETARY

CHIEFWARDEN

MESSMANAGER

Requisitions

Supplies

Payments

Daily rate

MenuOverdue bills

Ove

rdue

Paym

ents

to ve

ndors

Item

s ne

eded

each

day

Peri

shable

items

Bills

Rebate

s

/Extras note

DFD’S ARE DIFFERENT FROM FLOW CHARTS

A GOOD DFD SHOULD NOT HAVE……

LoopsCrossing linesData flow split into flows with different names and meanings.

GOOD STYLE IN DRAWING DFD

Use meaningful names for data flows, �processes and data stores.

Use top down development starting from �context diagram and successively levelling DFD

A process can only transfer input to �output.It cannot create new data

Data stores cannot create new data�

RULES OF DATA FLOW

Data can flow from external entity to process process to external entity process to store and back process to process

Data cannot flow from external entity to external entity external entity to store store to external entity store to store

LEVELLING OF DFD’S………

LEVELLING RULES If a process numbered ‘p’ levelled into n

processes, then each new process is numbered p1,p2,………pn respectively.

All data flows entering a process must also enter its levelled DFD.

All data flows leaving a process must also leave its levelled DFD.

No external entites may appear in lower level DFD’S.

Logical and physical DFD’S…

PHYSICAL DFDs…

VENDORCheckin

gclerk

storesclerk

Rejected note

inventory

Acceptednote

order

LOGICAL DFDs…

VENDORcheckin

gdelivery

Storesclerk

Rejected note

inventory

order

Acceptednote