G045 Lecture 08 DFD Level 1 Diagrams (Data Flow Diagrams Level

1)

Mr C JohnstonICT Teacher

www.computechedu.co.uk

Session Objectives

Understand what a level 1 diagram shows, Know the common components of a level 1

diagram, Be able to draw level 1 diagrams for given

scenarios,

Level 1 Data Flow Diagrams

Level 1 diagrams expand the main box within the context diagram and show what happens to the data within the system

They are made up of external entities, data flows, processes and data stores,

They are drawn using a standard set of symbols The data flowing into the system at level 1 must match

the context diagram.

Level 1 DFD Components

External entities interact with the system (people etc) but not actually part of it – they put data into the system or receive from it. They are represented in an ellipse with their name clearly displayed

Data stores are where data is stored. Data can be written or read from a data store. On the diagram that have a sensible name and could be computerised or manual system such as filing cabinets

Data flows indicate the direction of information flowing around the system. They are labelled arrows with the head showing direction of flow.

Processes are activities which take place in the system – normally it involved some sort of transformation to the data and have at least one data input and output. Processes are numbered on the diagram in order and have a label which include a verb.

Level 1 DFD Symbols

M1 Customer File

Data stores – labelled with a type, a number and the nameType is either M for manual or D for computerised store and the numbers counts up how many there are in the system

Customer Customer

External Entities – labelled with the nameThe ellipse with the slash across is used to repeat an entity later in the diagram to ensure its neat

1

Add new customer

Processes – numbered and labelled with a verb Rectangle has number of process (this is in order which it happens) and a label which states the process – uses a verb

Data Flows Arrow head shows the direction of the flow, should have a simple meaningful label describing the data

Drawing Diagrams Start by reading a scenario and summarising what is

going on into a table. Use the table drawn for the level 0 to help but notice this one has much more detail about the activities.

Activity Activity Overview Activities Documents Used

Activities become processes and documents used become data stores

Example Reporting day data is complied by a system at Stringer. Staff enter grades into the system for each student which includes their ID, a current working at grade and effort for a subject. The system stores them, compares with past data and generates a grade report for parents. Summary information is also generated for year heads showing subject grades for each student in the year and one for form tutors summarising their tutees performance.Activity

Activity Overview

Activities Documents Used

1 Entering Grades ID entered and subjects studied returned, Working at grade and effort entered

Student databaseGrade database

2 Comparison of grades Newly entered grades compared with old grades – comparison result added to file

Grade database

3 Generate full reports Students details and all grades complied into an A4 report

Student databaseGrade database

4 Generate summary reports

Tabular reports complied group by tutor group and year – listing each students past and present marks

Student databaseGrade database

PARENTSGrade Information

Student ID, working grade and effort

STAFF

Year group summary grades

Tutor group summary grades

YEAR HEAD

FORM TUTORS

Student ID

Student DetailsSTUDENT DB

1Student records retrieved from

student database – new grades appended

to grade database

D1 Grades

Student ID, subject ID, reporting day ID,working grade and effort

2New and old grades

compared – comparison result appended to grade

database

working grade and effort

3Student reporting day

reports compiled

4Summary reports

produced grouping by year and tutor group

working grade and effort

D1 Grades

working grade and effort

gradecomparisonresult

Student ID

Student Details

STUDENT DB

Student ID

Student DetailsSTUDENT DB

Summary

Read the scenario and work out the activities which go on within the system,

Draw the table listing the activities in order, what happens to the data and where it gets stored in the system,

Turn the table into a data flow diagram – Activities become processes Where the data is kept becomes data stores Data flows connect the processes and data stores Data enters and leaves the system to and from external entities

Check that the flows entering and exiting the system match what is on the level 0 diagram.

Exercises An insurance company system takes details from customers which includes personal, car and past claim data. The information acquired is complied and pasted onto an external broker which generates quotes. On return from the broker the best quote is formatted appropriately and sent to the customer.

The university and college admission system (UCAS) handles applications to higher education by students in the UK. Students submit data to the system which includes personal details, estimated grades, courses and institutions they want to apply for and a personal statement. A tutor also submits a reference for each student into the system. The system compiles each students application and forwards it onto the institution applied for. Upon receipt the staff at the university scrutinise the application and return to UCAS an offer or rejection – this is then passed onto the student.

BROKERCustomer details

Personal, car and past claim data

CUSTOMER 1Collate customer

details

D1 Customer File

Collated customer details

2Send details to broker Collated details

3Best quote selected and formatted and

stored

4Presented to the customer neatly

quotes D2 Brokers

Broker details

D3 Quotes

Formatted quotes

quotes

Best quoteCUSTOMER

D1 Customer File

Customer details

1Application Compiled

D1 Applications

Complied Applications

2Applications forwarded to

institutions and status updated

Application

3Application status

updated

4Offer / Rejection letter

compiled and sent

Response to application

D2 Institutions

Contact details

D1 Applications

Status

Application with decision

Offer / rejection STUDENT

D2 Institutions

Contact details

STUDENTPersonal data, est. grades, courses, institution data and personal statement

TUTOR Reference

INSTIUTIONApplicant Information Status update

Further Exercise Download the exercises below and read the instructions

carefully – draw the L1 diagrams as required. Further Exercise 1

Reservationof

Book

D StudentsStudent details

STUDENT

Loan Reservation

D BooksBook details

D ReservationReservations

Complete loan and mark book available

STAFF

Return Book Details D Loans

Loan details

D BooksBook details

Book marked available

Check for overdue books and calculate

how overdue

D StudentsStudent details

D BooksBook details

D Fines

Fine Value

s

Generate monthly reminder

Over due >21 days

D LoansLoan details

Calculate Fine, Generate Bill and Produce weekly staff

report

Tutor

Monthly list of students req

Billing letter

Over due >7 days

Generate Reminder

Over due < 7

days

Student

Reminder

D Tutors

TutorDetails

Library Staff

Billed Over dues

More Practice Spilt into pairs and develop a small scenario and solution which a L1 diagram could be drawn for. You will need to draw a L0 / Context diagram to help another pair draw their diagram.

Give you problem to another pair and ask them to draw a diagram before marking it and giving them the answer.

Assignment Link By next lesson draw a level 1 diagram for KASBAH NEWS’ Current System. Start by drawing a table to identify all the activities which go on, where the data is stored and when it enters and exits the system.Ensure you describe exactly what happens during each process - including any calculations, sorts and searches with the data,Ensure it matches you level 0 diagram before handing it in.

Task E What to Hand In Level 0 / Context

DiagramTable Describing External EntitiesTable Describing the data flows

Level 1Table used to construct the diagram (See slide 6)DiagramTable describing external entitiesDescription of the data stores (format / what

stored)Description of each process – what goes on