Transcript Lesson 1: Types of information

Lesson 5:
Steps for creating a L1 DFD
Step 1
 Read through the information collected about the processes.
 Use the information collected during the feasibility and investigation stages – if available.
Step 2
 Sort the information into clear sections, identifying the people or organisations external to
the system under investigation but who interact with it, the documents use in the system
under investigation, and the activities that take place within the system under
investigation.
Step 3
 Produce a data flow table (see incomplete data flow table for lovely lunches below).
ACTIVITY NO ACTIVITY OVERVIEW
DETAIL
DOCUMENTS USED
1
New order
Details of new orders taken –
start date, frequency of delivery
and products required.
Order book
2
Confirmation
Confirmation of new order
produced for customer.
Confirmation book
Step 4
 Convert external users to external entities.
Step 5
 Convert documentation to data stores.
Step 6
 Convert activities to processes, identifying when in the system the activity takes place,
who is involved and any data stores used.
Step 7
 Look at the inputs and outputs for each process with the data stores that are used, and
use data flows to ‘link’ these.
Step 8
 Link each data store and external entity with the associated process.
Step 9
 Link the processes (remember the rules about the labelling of processes!)
Step 10
 Check for consistency – check the initial findings to ensure all documentation has been
included, check that the flows between external entities given on the context diagram
are included, check with the end-users of the current system to ensure nothing has been
forgotten.
What now?
 Using the 10-step plan, you are now going to construct a L1 DFD for the complete system
used in the case study.