Transcript Spreadsheets in Finance and Forecasting

Spreadsheets in Finance
and Forecasting
Project Session
3b(ii)
Data Flow Diagrams
Objectives
After this session you will:
 know what is meant by a Data Flow
Diagram (DFD)
 recognise and be able to work with
DFD symbols
 Construct Context Diagrams and Top
Level DFDs to model data flow in a
system.
Dealing with Data
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We have already
discussed methods for
collecting data, and
some of the sources
that you might want
to explore.
In this session we
look at what you
should do with the
information that you
collect.
Modelling Data Flow
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We create models of
Data Flow in order to
understand and
document the
information on the
right:
There are several
different conventions
which can be used.
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Who or what initiates
the data (Data source)?
In what manner is it
processed, and who
does it?
Who uses the data?
In what manner and
where is the data
stored?
What is the output, and
who receives the data
(Data Target)?
Data Flow Diagrams (DFDs)
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DFDs model events and
processes within a
system.
Processes are activities
which transform data
DFDs examine how
data flows into or out
of a system
Note that data = any
“thing”, i.e.. raw
materials, information,
ideas etc, anything
which can be processed
DFD Questions
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What processing is
done?
When is it done?
How is it done?
Where is it done?
By whom is it
done?
DFD Questions
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What data is
needed?
For what is it
needed?
When is it needed?
By whom is it
needed?
Principles
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Every system can be decomposed into
subsystems, and those into lower
subsystems and so on.
Each sub system represents a process in
which data is modified.
Each process has the characteristics of a
system, and must have input & output.
Data flows into the system, flows
between processes and is then output
from the system.
DFD Notation
Processes
 transform or manipulate
data – “do this”
Data Flows
 show data going in to or
coming from a process
 flows must start or end at
a process
Data Stores
 where data is held
External Entities
 sources or targets for the
data
DFD Notation
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Process boxes are
numbered with a
unique identifier
(top left)
The top line gives the
location of or the
people responsible for
the process
Data Stores are also
numbered
The Context Diagram
The Context Diagram is an overall,
simplified view of the system, which
contains only one process box, and
the primary inputs and outputs
This example is
part of a “Home
Catalogue” sales
system
The Top Level DVD
The purpose of
this is to show
the major
processes which
are included in
the system
DFD Example
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A Health Club keeps
information on its members
Membership is subdivided
into Full, Daily and
Associate
On the 1st of each month,
the payments clerk checks
the records and sends out
reminders to members
whose subscription expires
this month.
When payment is received,
the subscription is renewed.
Context
Diagram
member
details
Members
The oval boxes are external to
the system. They are the
sources and targets of
information.
0 Club
receipt and
membership
details
In this case, the members are
both sources and targets and
the data flows in different
directions. The diagonal lines
indicate that they are actually
the same thing.
System for
Renewing
Membership
reminder
renewal
payment
details
Members
Level 1 DVD: Reminders
Payments
Clerk
memo on
1st Month
member
payment
status
member
ID
D1
name,
address
1 Office
Check
Records
member
ID
Payment Records
2 Office
Prepare
Reminder
reminder
Member
D2
Member Details
DFD Task
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What follows is a
description of a
situation involving the
flow of data in a
Theatre Booking
system
You should read the
description and try to
construct a context
diagram, and a Level
1 DFD
Theatre Example
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A theatre has a booking system , and keeps
records of customers, plays and seat bookings
A customer may make a booking in person, by
telephone or by a pre-printed form
At the time of booking, a clerk checks to see if
seats are free; if so, she reserves the seats and
checks to see if the details of the customer are
on the file; if they are not, she types them in.
Tickets are then printed and handed or sent to
the customer
Payment can be in cash or by credit card.
Finally
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A solution to the
Theatre problem
will be available
next week.
On the resource
sheet is an
important link
which develops the
ideas of DFDs
much further