1. G045 Lecture 08 DFD Level 1 Diagrams (Data Flow Diagrams Level 1)
Mr C Johnston
ICT Teacher

2. 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,

3. 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.

4. 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.

5. Level 1 DFD Symbols 1 Add new customer Customer Customer
External Entities – labelled with the name
The ellipse with the slash across is used to repeat an entity
later in the diagram to ensure its neat
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
M1 Customer File
Data stores – labelled with a type, a number and the name
Type is either M for manual or D for computerised store
and the numbers counts up how many there are in the system
Data Flows
Arrow head shows the direction of the flow, should have a simple meaningful label describing the data

6. 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

7. 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 database
Grade database 2
Comparison of grades
Newly entered grades compared with old grades – comparison result added to file 3
Generate full reports
Students details and all grades complied into an A4 report 4
Generate summary reports
Tabular reports complied group by tutor group and year – listing each students past and present marks

8. 1 2 D1 Grades 3 D1 Grades 4 STAFF STUDENT DB STUDENT DB PARENTS
Student ID,
working grade
and effort
STAFF 1
Student records retrieved from student database – new grades appended to grade database
D1 Grades
Student ID, subject ID, reporting day ID,
working grade and effort
Student ID
Student Details
STUDENT DB 2
New and old grades compared – comparison result appended to grade database
working grade
and effort
grade
comparison
result
Student ID
Student Details
STUDENT DB 3
Student reporting day reports compiled
D1 Grades
working grade and effort
PARENTS
Grade Information
working grade and effort
Year group
summary grades
Tutor group
YEAR HEAD
FORM TUTORS 4
Summary reports produced grouping by year and tutor group
Student ID
Student Details
STUDENT DB

9. 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.

10. 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.

11. 1 2 D1 Customer File D2 Brokers 3 D3 Quotes 4 D1 Customer File
Personal, car
and past claim
data
CUSTOMER 1
Collate customer details
D1 Customer File
Collated customer details 2
Send details to broker
BROKER
Customer details
Collated details
quotes
D2 Brokers
Broker details 3
Best quote selected and formatted and stored
D3 Quotes
Formatted quotes
quotes 4
Presented to the customer neatly
Best quote
CUSTOMER
D1 Customer File
Customer details

12. 1 2 D1 Applications D2 Institutions 3 D1 Applications 4
STUDENT
Personal data, est. grades, courses, institution data and personal statement 1
Application Compiled
TUTOR
Reference
D1 Applications
Complied Applications 2
Applications forwarded to institutions and status updated
Application
INSTIUTION
Applicant
Information
Status update
Response
to application
D2 Institutions
Contact details 3
Application status updated
D1 Applications
Status
Application with decision 4
Offer / Rejection letter compiled and sent
Offer / rejection
STUDENT
D2 Institutions
Contact details

13. Further Exercise
Download the exercises below and read the instructions carefully – draw the L1 diagrams as required.
Further Exercise 1

14. Complete loan and mark book available
STUDENT
Loan Reservation
D Students
Student details
Reservation of
Book
D Books
Book details
D Reservation
Reservations
STAFF
Return
Book Details
Complete loan and mark book available
D Loans
Loan details
D Books
Book details
Book marked available

15. D Loans D Books D Students D Tutors D Fines Tutor Student
Loan details
Check for overdue books and calculate how overdue
D Books
Book details
D Students
Student details
Over due >7 days
Over due < 7 days
D Tutors
Over due >21 days
Generate
Reminder
Calculate Fine, Generate Bill and Produce weekly staff report
Generate monthly reminder
Tutor
Details
D Fines
Fine
Values
Student
Reminder
Billing
letter
Library Staff
Billed
Over dues
Tutor
Monthly list of
students req

16. 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.

17. 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.

18. Task E What to Hand In Level 0 / Context Diagram
Table Describing External Entities
Table Describing the data flows
Level 1
Table used to construct the diagram (See slide 6)
Table describing external entities
Description of the data stores (format / what stored)
Description of each process – what goes on