During systems development both processes and data must be modeled◦ Data modeling describes data used by system◦ Process modeling describes processes carried out by

system Level of detail

◦ Varies between highest summary and lowest detail◦ Structured tools enable level of detail to be varied

Restrict a single DFD to no more than six to eight processes

Use another tool to document the lowest level of detail but use no more than a single page.

B-3

Graphic representation of a system that uses a small number of symbol shapes to illustrate how data flows through interconnected processes ◦ Most natural way to document processes◦ Emphasis on processes rather than data

B-4

CompanyCustomer

Despatch Note + Goods

Order

Rejected Order

Context Diagram

Customer

Sales1Order

Rejected Order

Dispatch Note

2 Warehouse

Dispatch Goods

3 Accounts

Maintain Credit Ratings

D1 Credit Rating

Check Credit Rating

A Complete DFD

Data Flow Diagrams (DFDs) show:

•The processes within the system

•The datastores (files) supporting its operation

•The information flows within it

•The system boundary

•Interactions with external entities

DFDs consist of four symbols1) Environmental elements called terminators / external

entity Person Organization Another system

2) Processes which transform inputs to outputs Labeled with verb and object Also labeled with system or computer program name

B-8

DFD symbols [cont.]◦ Data flows which consist of logically related data elements

that travel from one point or process to another. In other words, data in motion. Structures Diverge Converge

◦ Data stores which are data repositories. In other words, data at rest.

B-9

Customer

Sales

Check Credit Rating

D1 Credit Rating

A Data Flow

An External Entity

A Process

A Data Store

3

DFD Symbols

Sales

Check Credit Rating

3

Unique Number Where it’s done

What’s done

Output DataInput Data

The Process Symbol

Accounts

Maintain Credit Rating

3

Sales

Check Credit Rating

1

M = Manual data Store

D = Computer File

D1 Credit Rating

Writing/Updating

Reading

The data store symbol

Sales

Check Credit Rating

3

D1 Credit Rating

The Data Flow Symbol

Customer Balance

Use Meaningful names

Self Evident Data Flows need

not be named

Physical Resource Flow

Customer

Returned

Library Book

The External Entity Symbol

Customer

System Boundary

A Source and/or sink of data outside the system boundry

Context Diagram Diagram 0 Child diagram (level 1, 2,…,n)

DFD dikelompokkan menjadi 2:◦ Logical DFD

Fokus pada bisnis dan bagaimana bisnis berjalan How the system will be constructed

◦ Physical DFD How the system will be implemented Include hardware, software, files, people yang

terlibat dalam sistem

2 Dispatch Goods

2

1

Process

2.1

Dispatch

Note

Validated

Order

Levelling – to avoid complex DFDs, processes can be grouped into higher level processes

Customer

Sales1Order

Rejected Order

Dispatch Note

2 Warehouse

Dispatch Goods

3 Accounts

Maintain Credit Ratings

D1 Credit Rating

Check Credit Rating

A Complete DFD

Customer

D1 Credit Rating

A Duplicated External Entity

Duplicated Data Store

Customer

Repeated Symbols – to avoid crossing lines, data

stores and external entities can be repeated:

Level 1

Level 2

E F D

Elementary

Functional

Description

Get cust dets

If order>cred

refer

Else

raise order

…..

DFD Levels

A wines and spirits wholesaler stocks a range of approximately 400 different lines and delivers by van on regular weekly runs to customers who are mainly off-licenses and clubs. The majority of orders are received by telephone and any one customer may place several orders during the week which must be accumulated and delivered in one consignment. When a customer telephones he expects to be advised on the availability of an item requested and, if not in stock, the alternatives that are available. At present, sales order forms are filled in by the telephone salesmen and sent to the warehouse where they are used for the despatch of the items. Hand-written despatch notes are used as the basis of the invoices which are typed and sent by post sometime later.

Prepare a dataflow diagram (DFD) which represents the above system.

Sample

Developing Dataflow Diagrams

1. Identify external entities

2. Draw context diagram

3. Who/Where does what

4. Identify datastores

5. Draw diagram

External Entities

1. Customer

Context Diagram

customer company

order

invoice

advice

des. note + goods

What Where/who

Receive orders Sales

Accumulate orders Sales

Advise availability Sales

Complete Sales Order Form Sales

Despatch Items Warehouse

Write despatch notes Warehouse

Type Invoices Warehouse

Send Invoices Warehouse

Datastore

Stock file

customer

customer

Stock file

Accumulate orders

Advise availability

Complete forms

1 Sales

Sales Order Forms

2

Produce despatch notes

Produce Invoices

InvoiceDespatch note + goods

Warehouse

Draw DFD

OrderAdvice

M1

Extensions

Maintenance of Stock File

Customer file – address, credit etc

Payments

Accounts dept – invoices, payments etc

Accumulate orders – temporary file