Importances of dependability
For many computer-based systems, the most important system property is the dependability of the system.
The dependability of a system reflects the user's degree of trust in that system.
It reflects the extent of the user's confidence that it will operate as users expect and that it will not fail in normal use.
The followings are importance of software dependability.
- System failures may have widespread effects iwth large numbers of people affected by the failure.
- Systems that are not dependable and are unreliable, unsafe, or insecure may be rejecte by their users.
- The costs of system failure may be very high if the failure leads to economic losses or physical damage.
- Undependable systems may cause information loss with a high consequent revory fast.
The principal dependability properties
Availability means 'Can client use the software whenever I want?'
Reliability menas 'Is it working as expected?'
Resilience menas 'How fast can you get it back on track when there's a problem?'
In addition, there are some other dependability properties.
- Repairability : It reflects the extent to which the system can be repaired in the event of a failure.
- Maintainability : It reflects the extent to which the system can be adapted to new requirements.
- Error tolerance : Reflects the extent to which user input errors can be avoided and tolerated.
Dependability costs
Dependability costs tend to increase exponentially as increasing levels of dependability are required.
There are two reasons for this.
- The use of more expensive development techniques and hardware that are required to achieve the higher level of dependability.
- The increased testing and system validation that is required to convince the system client and regulators that the required levels of dependability have been achieved.
Because of very high costs of dependability achievement, it may be more cost effective to accept untrustworthy systems and pay for failure costs.
System and software
