Systems Analysis Course

• Home
• 1.What is a System
  • Introduction
  • Parts of a System
• 2.System Lifecycle
  • Project Management
  • Project Lifecycle
  • Check Understanding
  • SDLC Comparison
  • Exercise
• 3.Feasibility Study
  • Sections
  • Exercise
• 4.CostBenefit Analysis
• 5.System Investigation
  • Introduction
  • Methods
  • Identify method
  • Exercise
• 6.Data Flow Diagrams
  • Introduction
  • Video
  • Definitions
  • Steps to create
  • Exercises
• 7.Relational Diagrams
  • Terminology
  • Examples
  • Exercise
  • Using a DFD level1
• 8.Data Dictionary
• 9.Design Specification
• 10.Creating a Test Plan

 

 

Lesson 6 - Data Flow Diagrams

Steps in creating a CONTEXT DIAGRAM (high level Data Flow Diagram DFD)

The following explanation will use the Rapid Results Driving School Scenario

The company has 8 driving instructors, who work various hours, and approximately 50 pupils who are learning to drive. Pupils request one or more lessons by ringing up, a booking clerk answers the telephone and adds the new lesson details to the lesson booking system. If it is a new pupil, their contact details are also recorded. 

Instructor's have diaries in which to record lesson information. An entry in the instructors diary is made at the end of each lesson that shows whether the pupil has attended and paid. At the end of the day, the instructors return to base, and input their updated lesson details into the lesson booking system.

Every evening the instructors are given a schedule of their lessons for the following day.

Every week the manager receives  a report detailing all lessons undertaken, all lessons cancelled and the total income from lessons.

Step 1

Work out sources and recipients of data in the Rapid Results Driving School system

To do this you need to list:

1. People and/or Job roles and/or Departments
2. Other organisations involved
3. Other systems

People/Job roles/Departments

Driving Instructors
Booking Clerk
Pupils.

Other organisations involved

None

Other systems

None

Step 2

Creating the CONTEXT DIAGRAM:

Each Source and Recipient becomes an external Entity. In the centre of your context diagram you need to draw a single process box.

Step 3

Add the Data flows, show the flow of data (INPUT and OUTPUT from the system). Data flow is any movement of information from a source to a recipient in the system. Information can be in the following forms:

• Verbal (telephone call, face to face or any other verbal form of communication)
• Written (letter, report or any other written form of information)

You need to label each Data Flow to state what the data flow is and use an arrow to show whether the data flow is INPUT or OUTPUT.

YOU HAVE NOW CREATED A CONTEXT DIAGRAM or HIGH LEVEL DFD

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Steps in creating a LEVEL 1 DATA FLOW DIAGRAM

Step 1.

Add the processes to the data flows in your Context Diagram. First take out the main process box from the centre of your diagram:

STEP 2 - Then add in each process box. As a rule each data flow requires at least one process box and each process should have a unique number. Processes are things that happen in the system and therefore should have the following kinds of words in them:

Update, Calculate, Save, Delete, Create, Read, Write, Enter, Make, Send

STEP 3

All of the data in your system needs to be stored in a data stores, so now you have to add the DATA STORES to your DFD – To work out the data stores required for your system think about the CATEGORIES of data required for your entities:

In this case there are three:

• Instructor details
• Pupil details
• Lesson details

You need to use an arrow to show the direction of data INPUT or OUTPUT from the data store to the process

YOU NOW HAVE A LEVEL 1 DFD

 

Copyright JK Nichols 2009