Data flow & information requirements. Establishing IPSO Recording information about the existing...
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Transcript of Data flow & information requirements. Establishing IPSO Recording information about the existing...
The Systems Life Cycle: Analysis 2
Data flow & information requirements
Objectives:
Establishing IPSO Recording information about the
existing system Identifying the problems with the
system Identifying User & Information
requirements of the new system Identifying HW & SW for a new
system.
So far….
Our analyst has collected information about the current system using questionnaires, observation, interviews and examining documents.
What happens next?
Step 2:
Need to identify all the inputs, processing & outputs in the existing system.
How?
1: Examination of documents
This allows the analyst to establish which documents relate to information coming IN to the system, and which relate to information going OUT.
What happens to this information?
The analyst uses this knowledge to produce his own documentation of the system which helps him understand the system properly.
Each section…
….needs to be examined to see the specific inputs, processes & outputs.
What would be the inputs of a payroll system?
The processes? The outputs?
2 : Recording information about the current system
All results of fact-finding must be recorded
Accurate records are vital – why? Because the system will
evolve Other analysts &
programmers will need to develop the system even further at some point in the future.
How do we record the flow of data?
Data flow diagrams These are a graphical
method of recording the inputs, processing & outputs that have been identified.
Flow charts vs DFDs
Flow charts show the control flow of the program
DFDs show how the data flows around the entire system
3 : DFDS….
Data flow diagrams illustrate how data is processed by a system in terms of inputs and outputs.
Have four components: Terminators Processes Flow arrows Stores
An example
Process
order
Customers
Orders
Rejected Orders
Orders
InvoicesIn
voice
dat
a
Order
Info
rmat
ion
An explanation
CustomersA Terminator - someone or something outside the system (eg a customer or a supplier)
InvoicesData stores – where stored on paper or on a computer
Data flow. It is important that the direction of the flow is accurately recorded.
Process
order
Process order
Different levels of DFDs
Level 0 Very generalised Shows terminators linked
to current system eg 0Customers
Order Processing system
Customers
Different levels of DFDs
Level 1: Many more processes More detail Process boxes for both
receiving orders and for producing invoices 1
Different levels of DFDs
Level 2: These show all aprts of
the level 1 diagram in much more detail 2
DFDs:
Represent the way that data flows around the existing (old) system
System flowcharts
May be used, but generally are found in the design stage.
Represent the new system – the one that is going to be designed & implemented.
4 : Identifying problems with the current system
DFDs help the analyst to identify problems or weaknesses within the current system: Eg data duplication Job duplication Unnecessary steps
Why is it necessary to identify these problems?
5 : Identifying suitable hardware & software for the new system
DFDs help the analyst decide on: Appropriate methods of
input Approximate processor
speed & memory Size & number of
storage devices Quantity & format of
output
6: Identifying the user & information requirements
The new system MUST meet the needs of the people who will use it
So – the analyst needs to know exactly what job each person does and what their requirements are.
He can the produce a Requirements Specification – a list of features of the system that are required.
Analysis Summary
Step 1 : collecting information on how the current system works
Step 2 : Establishing inputs, processes & outputs
Step 3 : recording information Step 4 : Identifying problems Step 5 : Identifying suitable hardware &
software Step 6 : Identifying user & information
requirements