Data Flow Data Flow DiagramsDiagrams

An Introduction to Level 0 and An Introduction to Level 0 and Level 1 DFD’s.Level 1 DFD’s.

What is a DFD?What is a DFD?

A data flow diagram is a…A data flow diagram is a…

What is Level 0 DFD?What is Level 0 DFD?

Level 0 shows the main system and Level 0 shows the main system and what data or objects are passed to/from what data or objects are passed to/from external entities.external entities.

– If the system is a whole company, external If the system is a whole company, external entities are people who do not work in the entities are people who do not work in the company being modelled or other company being modelled or other companies.companies.

– If the system is a department, external If the system is a department, external entities are other departments or people entities are other departments or people who do not work in the dept being modelled.who do not work in the dept being modelled.

Worked ExampleWorked Example

Your TurnYour Turn

How to create a Level How to create a Level 0 dfd.0 dfd. Make the following headings in your Make the following headings in your

jotter:jotter:– System Name;System Name;– External Entities;External Entities;– Data Flow; &Data Flow; &– Physical Flow.Physical Flow.

Go through the passage and write Go through the passage and write down any of the above under the down any of the above under the headings.headings.

Worked Example - Worked Example -

System NameSystem Name

External EntitiesExternal Entities

Data FlowData Flow

Physical FlowPhysical Flow

Now you do Your turn -

Your Turn - Your Turn -

System NameSystem Name

External EntitiesExternal Entities

Data FlowData Flow

Physical FlowPhysical Flow

Now you do Your turn -

How to create a Level How to create a Level 0 dfd.0 dfd. The system name goes in a hard The system name goes in a hard

box in the middle of the page.box in the middle of the page.

<System Name>

How to create a Level How to create a Level 0 dfd.0 dfd. Each external entity goes in an oval box Each external entity goes in an oval box

either to: the left and right if there are two; either to: the left and right if there are two; left, right and bottom if there are three; or left, right and bottom if there are three; or left right bottom and above if there are 4.left right bottom and above if there are 4.

<System Name>Entity 1 Entity 2

Entity 3

Worked ExampleWorked Example

<System Name>Entity 1 Entity 3

Now you do Your turn -

Your TurnYour Turn

<System Name>Entity 1 Entity 3

How to create a Level How to create a Level 0 dfd.0 dfd. Add in data flow: Add in data flow:

– use a thin line with an arrow showing the use a thin line with an arrow showing the way the data flows.way the data flows.

– write the name of the data flow on the write the name of the data flow on the line. line.

Add in physical flow:Add in physical flow:– use a thick line with an arrow showing the use a thick line with an arrow showing the

way the physical flows.way the physical flows.– write the name of the physical flow on the write the name of the physical flow on the

line.line.

Worked ExampleWorked Example

<System Name>Entity 1 Entity 3

Now you do Your turn -

Your Turn - Your Turn -

<System Name>Entity 1 Entity 3

Well Done!Well Done!

That is how you create That is how you create level 0 DFD’slevel 0 DFD’s

TasksTasks

Task 1Task 1

Task 2Task 2

What is a Level 1 dfd’sWhat is a Level 1 dfd’s

A level 1 dfd is a diagramatic A level 1 dfd is a diagramatic form of showing the main form of showing the main processes, data flows and data processes, data flows and data stores within the system.stores within the system.

How to create Level 1 How to create Level 1 dfd’sdfd’s

When creating a level 1 dfd go back When creating a level 1 dfd go back and read the description! (VERY and read the description! (VERY IMPORTANT ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !)IMPORTANT ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !)

Write down the following Headings:Write down the following Headings: External EntityExternal Entity ProcessesProcesses Data FlowsData Flows Data StoresData Stores

How to create Level 1 How to create Level 1 dfd’sdfd’s

As you read through the passage As you read through the passage (again) write down the relevant (again) write down the relevant information under the headings information under the headings above.above.

This will be used as a check list This will be used as a check list after creating the dfd.after creating the dfd.

Worked Example – Worked Example – School EnrolmentSchool Enrolment

External EntityExternal Entity StudentStudent

ProcessesProcesses Record student applicationRecord student application Check course availabilityCheck course availability Check student qualificationsCheck student qualifications Enrol student in courseEnrol student in course Update application fileUpdate application file

Worked Example – Worked Example – School EnrolmentSchool Enrolment

Data FlowsData Flows Application formApplication form Course Applied forCourse Applied for Student QualificationsStudent Qualifications Results from course and student checksResults from course and student checks Course and student detailsCourse and student details Confirmation letterConfirmation letter Rejection letterRejection letter

Data StoresData Stores Application fileApplication file Course Details FileCourse Details File Enrolment FileEnrolment File Your turn – order processing

Your Turn – Order Your Turn – Order ProcessingProcessing

External EntityExternal Entity CustomerCustomer WarehouseWarehouse

ProcessesProcesses Process customer detailsProcess customer details Process order detailsProcess order details Complete picking slipComplete picking slip Process invoice and shipping statementProcess invoice and shipping statement

Worked Example – Worked Example – School EnrolmentSchool Enrolment

Data FlowsData Flows Customer detailsCustomer details Order detailsOrder details Picking slipPicking slip Order CopyOrder Copy InvoiceInvoice Shipping statementShipping statement

Data StoresData Stores Customer File (D)Customer File (D) Orders Folder (M)Orders Folder (M)

How to create Level 1 How to create Level 1 dfd’sdfd’s

Processes are drawn using a Hard Processes are drawn using a Hard Box :Box :

Files are drawn as follows:Files are drawn as follows:

<process1>

D1 <File 1>

Data Flow is drawn the same as Data Flow is drawn the same as at level 0.at level 0.

How to create Level 1 How to create Level 1 dfd’sdfd’s

Read each sentence of the Read each sentence of the description carefully.description carefully.

As you read the sentence draw As you read the sentence draw that part of the dfd using the key that part of the dfd using the key on the previous page.on the previous page.

When you have finished use your When you have finished use your checklist to make sure you have checklist to make sure you have included all your processes, files included all your processes, files etc.etc.

Working Example – Working Example – Student enrolmentStudent enrolment

student

applicationApplication Processing

D1 Application FileAdd application details

Check courseDetails

D2

Course details

Course Details

Course Details File

Check studentQualifications

Student details

Course Details

Enrolment Process

Confirmationletter

Checking results

D3 Enrolment FileStudent Details

D1 Application File

Update

rejectionletter

Your turn – order processing

Your Turn – Order Your Turn – Order ProcessingProcessing

Customer

Order Processing

D1 Customer File

Add customerdetails

CustomerDetails

orders

M1 Order FolderOrder details

Complete Picking Slip

Warehouse

Copy of Order

Picking SlipCopy of order

Picking Slip

Create invoice/Shipping statement

Copy oforderInvoice

Shipping Statement

Task – school Task – school applicationapplication

Now do the level 1 dfd for school Now do the level 1 dfd for school application.application.

Way Hay – Now you can do level 1 Way Hay – Now you can do level 1 dfd’s! Well Done!dfd’s! Well Done!