Representation of Data Flow and Information

Edited by: Yudi Priyadi Email: whyphi @ yahoo.com http://www.facebook.com/whyphi Hp:

Representation of

Data Flow and Information

1

Source: www.yourdon.com

©2006 Ed Yourdon - rev. 013106


Concept of Data Flow Diagram

➢ IPO: Input →Process → Output

Data→ Process → Information

➢ Data flow diagram is a graphical technique that depicts

information flow and the transforms that are applied as

data moves from input to output.

➢ DFDs use four basic symbols that represent

processes, data flows, data stores, and entities

• Gane and Sarson symbol set

• Yourdon symbol set




Symbols for DFD

Data store

Process

name

External

Interactor

External Entity:

Source or destination of data

Process:

Action on data

Data Store:

Storage of data

Data Flow:

Data Transfer

Yourdon notations (source: www.yourdon.com)




Creating a Set of DFDs

❑ Create a graphical model of the

information system based on your

fact-finding results

❑ Performing three main tasks

▪ Step 1: Draw a context diagram

▪ Step 2: Draw a DFD level 1

▪ Step 3: Draw the lower-level diagrams




Draw a Context Diagram

➢ Drawing Guidelines1. Draw the context diagram so it fits on one

page

2. Use the name of the information system as

the process name in the context diagram

3. Use unique names within each set of symbols

4. Do not cross lines

5. Provide a unique name and reference

number for each process

6. Obtain user input and feedbackSource: www.yourdon.com



External Entity

❑ External entity represents the sources and

destination of data created by the system.

❑ External entity represents the immediate interface

of the system with the external world.

❑ When an external source of data is also a

destination for data, a loop or occurrence number

may be used.

❑ In case the destination or use of data created by

the process are not known, the flow simply points

outside the system. Similarly, data flows may

originate from “nowhere”.




Process Boxes

❑ Each processes box in a DFD describes an action

on data.

❑ The Identifier. A number indicating the sequence

of the process.

❑ The Action. A verb specifying the action on

which it is performed on the data.

❑ The Actor or Place. A noun indicating who

performs the action or where it is performed.




Data Flow Arrows

❑ Data flow arrows link all the process boxes and

data stores in DFDs.

❑ Data flows should be labeled, except in case the

data flows into and out of simple files.

❑ DFDs show only the flow of data, not materials.

❑ A DFD depicts information flow without explicit

representation of procedural logic (e.g.,

conditions or loops).




Data Store Rectangles

❑ Data stores can be manual files or computer files.

The type of file is not indicated.

❑ Only in case the data store is altered the flow is

not indicated. A simple access is not indicated.

❑ A data store is never the direct recipient of

unprocessed data from external sources or from

other data stores nor is data from a data store

ever directly delivered to an external sources.

There must be a process step in between.




Rules for Constructing DFD




DFD Not Allowed Flows




DFD Not Allowed Flows

If part of our system

If not part of our flow ignoreSource: www.yourdon.com



Data Flows

➢ Only one direction of flow between

processes




Data Flows

➢ Joins & forks allowed only if exactly the

same data




Data Flows

❑ Cannot go directly back to the process it

leaves

❑ The figure incorrect if .........




DFD Rules

Incorrect Correct




DFD Rules

Incorrect Correct




DFD Rules

Incorrect

Correct




Examples of Data Stores

Read

Write

Read/

Write

A data item is created

or deleted or updated in the

data store by

a processSource: www.yourdon.com



Example E1 E2

E3E1

E2

E3

1

4 2

E1 E2

E3



A balanced DFD Fragment

source: www.yourdon.com

Edited by Yudi Priyadi

Level 0

Level 1

Level 2

Level n…

http://yourdon.com/strucanalysis/wiki/index.php?title=Image:Figure922a.jpg


Level 0 DFD (Context Diagram)

Entity A

Entity D

0

System

Name

a

b

c

z

r

Entity C

Entity B

Keterangan:

a: .........

b:...........

c:.......... dst



Y


Level 1 DFD

1

Pro A

a

b

c

z

r

2

Pro C

3

Pro B

4

Pro D

5

Pro E

d

e

f

g h

i

Entity A

Entity B

Entity C

Entity D

n

p

dtstore1

dtstore2



Y


Level 2 DFD

c

f

2.1

Pro F

2.2

Pro G

2.3

Pro HEntity B

m

k

j

dtstore3

4

Pro D




Balancing

➢ The conservation of input and output flows

through different levels

A

B

C

A

B

C

D

E




Data Flows

❑Data which moves together should be

shown in a single data flow

itemised calls

invoice

invoicepayment

itemised callsAnd invoice

Pay

Invoice

Telephone

Company

Pay

Invoice

Telephone

Company

invoicepayment



………

………


Example of Context Diagram(Let’s check with the rules together ^^ ...)



TRUE ? or FALSE ?


Example of DFD Level 1(Let’s check with the rules together ^^ ...)



TRUE ? or FALSE ?


Context Diagrams

(incomplete !!)

❑ A context diagram is a top level (also known as Level 0) data flow diagram.

❑ It only contains one process node (process 0) that generalizes the function of the entire system in relationship to external entities.



Edited by: Yudi Priyadi Email: whyphi @ yahoo.com http://www.facebook.com/whyphi Hp:29

© 2010 Bennett, McRobb and Farmer

Context Diagram

Agate

Campaign

Management

System

Campaign

Manager

Client

Budget

Campaign

Staff

Campaign

Advert

Staff Assignment

Accountant

Concept Note

StaffConcept Note

Staff

Staff Grade

Staff

Contact

Payment

Advert Completion

Client Contact

(Let’s check with the rules together ^^ ...)



TRUE ? or FALSE ?



Level 1 Diagram

1.

Record

Clients

Campaign

Manager

Client

Staff Assignment

Campaign

Staff

Campaign

Advert

Accountant

Concept Note

Staff

Concept

Note

Staff

Staff Grade

Staff

Contact

Payment

Advert Completion

Client Contact

3.

Prepare

Adverts

Notes

6.

Browse

Concept

Notes

Concept

Note

Concept Note

4.

Maintain

Staff

5.

Manage

Adverts

Adverts

Advert

Contact

+ Completion Date

Clients

Client

2.

Plan and

Manage

Campaigns

Staff Members

Staff

Budget

Cost

Concept

Note

Campaigns

Campaign

Staff

Staff






Level 2 Diagram

5.1

Set Client

Contact

Adverts

Contact

Staff Members

Staff

Completion Date5.2

Set Advert

Completed

Staff

Contact




TRUE ? or FALSE ?

Documents

Representation of Data Flow and Information