2. DATA ANALYSIS
Identifying the data needed for the business to operate is the next
step. You need to find where the data comes from, what information is
processing that data, and who the output goes to.
Data-flow diagrams are the best way of showing how data works in a
system
The notation used for this is shown over the next few slides.

3. DATA STORE
Any place where data is held. In a manual
system this may be in an address book, a
directory, or a set of invoices; in a computer it
is generally a file of some sort.
D1 Customer

4. PROCESS
Any action that causes something to happen to some data, making
a change or converting it into information. In a manual system this
could be looking up a phone number in a directory, writing a phone
number down in an address book, or calculating a total and putting
it at the bottom of an invoice. In a computer it could be automatic
calculation of the total, or producing a list of patients and
appointment times. All processes have input and output –
something going in and something coming out. With data-flow
diagrams, it is processes involving data that are included.

5. DATA FLOW
Used to show how data moves into, between and out of
processes, and between sources and recipients (destination) od
data. These may be people, institutions or other systems. Data
flow is not the physical article but the data that accompanies it –
not the stock item itself, but the order, the picking list, the delivery
note, the bill/ or the receipt.

6. SOURCES OF DATA AND RECIPIENTS
Sources of data:
Those external entities that provide data for the system. These
may be customers, who provide order details, or suppliers, who
provide delivery notes and invoices.
Recipients (destinations) of data:
Those external entities who receive output from the system, but
do not directly use it. For example, government departments
receive tax returns from payroll systems, and VAT returns from
accounting systems; the board of governors at a school receives
performance and financial reports.

7. CONTEXT DIAGRAM / LEVEL 0 DFD
Data-flow diagrams can be drawn at different levels, to show levels of process. If
a process is not a single step, a further Diagram is required to show the
breakdown. Each Process is numbered, with the system being numbered 0. An
example for a catalogue system is shown over the next few slides. The diagram
below shows a basic data flow from customer to the system.
Rejected
order
0
Custome Order
r
Catalogue System
Goods

8. LEVEL 1 DFD
The level 1 data-flow diagram (DFD) below breaks the system into three main
processes, the first to check whether the customer is credit-worthy, the second to
deal with the order of goods, finding them, picking them and sending them to the
customer, and the third to maintain the credit details held for existing customers.
The arrow with the question mark indicates that there needs to be some input for
this process, but as yet, the analyst does not know who or where this will come
from.
1
Check credit rating Credit
Order details
Validated
Rejected Order
Custome 2
Order D1 Credit Rating
r Dispatch Goods
Goods
? 3
Maintain Credit
Amended
credit
Rating
details

9. LEVEL 2 DFD
The level 2 DFD for process 1 is shown below. Process 2 is likely to break down
to at least one more level as well, more likely two or three more levels. Notice
how the numbering system works. The lines surrounding this DFD show the
boundaries of the process - the external entity ‘Customer’ and the data store
‘Credit rating’ are held outside the process.
1 Check Credit Rating
1.1
Order Credit
Receive Order
Details D1 Credit Rating
Custome Received
r Order 1.2
Check Cred. Status
Reject Okay
Order Order
Rejecte
d Order 1.3 1.4 Validated
Order
Send Rejection Send Order to Dispatch
?

10. FINALLY
Data-flow diagrams may be used
for documenting the current
system, but are more useful when
designing the proposed system.