Since nobody is perfect and we always make mistakes, any errors created within the system development life cycle can lead to so many faults within the software, which will eventually lead to the failure of the software.

 

• Error – Mistake made by human.

 

• Fault – The result of an error also known as bugs or defects.

 

• Failure – The result of the fault. This leads to the deviation of the software from its expected results.

 

If a system has been well tested to the agreed specification, the result should be a reliable system that does what the user requires it to do.

 

Generally, the more faults or defects that are detected and corrected the more reliable the system will be.

It is also important that the testing carried out reflects the real use of the system.

 

In a business critical system, how reliable should the software be?

 

It is perhaps definitely right to say that a business critical system that would be used 24hrs 7 days a week should be very reliable than one that is not that critical and not that used on daily basis.

If correct, then, we now have to answer the question that, "how can reliability be measured?"

 

Reliability can only be measured over time.

 

It is impossible to test every aspect of the system so a hundred percent reliability cannot be guaranteed.

However, by assessing the importance of the business processes contained within the system, more emphasis can be placed on the testing of those areas, thereby reducing the possibility of failure in these areas.

 

Therefore we can conclude on the following facts about reliability, which are that: -

 

• Reliability is designed into systems.
• Reliability is specified at start of project.
• Reliability is very difficult to test.
• Reliability is measured over time.