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