An Introduction to Level 0 and Level 1 DFD’s. Data Flow Diagrams An Introduction to Level 0 and Level 1 DFD’s.

What is a DFD? A data flow diagram is a…

What is Level 0 DFD? Level 0 shows the main system and what data or objects are passed to/from external entities. If the system is a whole company, external entities are people who do not work in the company being modelled or other companies. If the system is a department, external entities are other departments or people who do not work in the dept being modelled.

Worked Example

Your Turn

How to create a Level 0 dfd. Make the following headings in your jotter: System Name; External Entities; Data Flow; & Physical Flow. Go through the passage and write down any of the above under the headings.

Worked Example - System Name External Entities Data Flow Physical Flow Now you do Your turn -

Your Turn - System Name External Entities Data Flow Physical Flow Now you do Your turn -

How to create a Level 0 dfd. The system name goes in a hard box in the middle of the page. <System Name>

How to create a Level 0 dfd. Each external entity goes in an oval box either to: the left and right if there are two; left, right and bottom if there are three; or left right bottom and above if there are 4. Entity 1 Entity 2 <System Name> Entity 3

Worked Example Now you do Your turn - Entity 1 Entity 3 <System Name> Now you do Your turn -

Your Turn Entity 1 Entity 3 <System Name>

How to create a Level 0 dfd. Add in data flow: use a thin line with an arrow showing the way the data flows. write the name of the data flow on the line. Add in physical flow: use a thick line with an arrow showing the way the physical flows. write the name of the physical flow on the line.

Worked Example Now you do Your turn - Entity 1 Entity 3 <System Name> Now you do Your turn -

Your Turn - Entity 1 Entity 3 <System Name>

Well Done! That is how you create level 0 DFD’s

Tasks Task 1 Task 2

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

How to create Level 1 dfd’s When creating a level 1 dfd go back and read the description! (VERY IMPORTANT ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !) Write down the following Headings: External Entity Processes Data Flows Data Stores

How to create Level 1 dfd’s As you read through the passage (again) write down the relevant information under the headings above. This will be used as a check list after creating the dfd.

Worked Example – School Enrolment External Entity Student Processes Record student application Check course availability Check student qualifications Enrol student in course Update application file

Worked Example – School Enrolment Data Flows Application form Course Applied for Student Qualifications Results from course and student checks Course and student details Confirmation letter Rejection letter Data Stores Application file Course Details File Enrolment File Your turn – order processing

Your Turn – Order Processing External Entity Customer Warehouse Processes Process customer details Process order details Complete picking slip Process invoice and shipping statement

Worked Example – School Enrolment Data Flows Customer details Order details Picking slip Order Copy Invoice Shipping statement Data Stores Customer File (D) Orders Folder (M)

How to create Level 1 dfd’s Processes are drawn using a Hard Box : <process1> Files are drawn as follows: D1 <File 1> Data Flow is drawn the same as at level 0.

How to create Level 1 dfd’s Read each sentence of the description carefully. As you read the sentence draw that part of the dfd using the key on the previous page. When you have finished use your checklist to make sure you have included all your processes, files etc.

Working Example – Student enrolment Add application details D1 Application File student Application Processing application D2 Course Details File Course details rejection letter Checking results Course Details Check course Details Student details Confirmation letter Course Details Check student Qualifications Enrolment Process D3 Enrolment File Student Details Update D1 Application File Your turn – order processing

Your Turn – Order Processing Customer File Customer orders Add customer details Customer Details Order Processing M1 Order Folder Order details Copy of Order Picking Slip Complete Picking Slip Copy of order Warehouse Picking Slip Copy of order Invoice Create invoice/ Shipping statement Shipping Statement

Task – school application Now do the level 1 dfd for school application. Way Hay – Now you can do level 1 dfd’s! Well Done!