A level revision

Analysing a system

The purpose of analysing a current system is find out the requirements for any proposed new system, what data needs to be handled, how it should be handled and who will be using the system.

Fact finding techniques

To find out information about a system a number of methods are available:

• Surveys and questionnaires can be used to get the opinions of lots of people with relative ease. They are cheap but limit the amount of feedback a user can give.
• Observations involve spending time watching the current system in use. This allows you to pick up on things the others may not and spot ways to improve the system.
• Interviews are the most useful way of fact finding, they are cheap and easy to conduct plus give the interviewee a chance to respond to your replies to their feedback. However they require more time and planning, a good interviewer needs to know what to ask, who to interview, where and when.
• Examination of paperwork allows you to see what information, types and amounts, the current system handles and how much the new system must be expected to handle

Reporting techniques

Diagrammatic ways are used to report the findings of the analysis.

Data flow diagrams

Data flow diagrams show:

• where the data in the system originates
• what processing is performed
• who uses the data
• where the data is stored
• What is output

Data flow diagrams comprise of 4 main symbols:

The entity symbol represents a source or destination of data (e.g. a customer to receives an invoice)

The data store symbol represents a data storage such as a hard disk

The process symbol represents some sort of processing which is performed on the data. Information on the process (e.g. validate inputted address) is put in the middle box

The data flow symbol shows which way data moves between processes entities and data stores

Here is a simple example:

Here the entity Employee provides the hours they have worked. This, together with their hourly pay rate from the employee data store is processed to calculate how much they are to be paid. A pay check is then given to the employee.

Levelled DFDs

Data flow diagrams can be represented by different levels by splitting the system into successively more detailed diagrams. For example a the top level of a payroll system may have a single process called 'calculate payroll'. The second level may split this single process into 3 others: calculate hours worked, calculate earnings, deduct tax and expenses