Related characteristics
maturity
fault tolerance
recoverability
availability
degradability
Fault Tolerance
Description
Attributes of software that bear on its ability to maintain a specified level of performance in cases of software faults or of infringement of its specified interface.
Indicators
1. disturbances
The number of times processing halted due to incorrect use within a certain period.
Source: QUINT
Scale: ratio
Validity: ***
Protocol:
1. Determine the period of measurement;
2. Register the number of times that processing halts;
3. Evaluate in which case this was caused by incorrect use.
2. vulnerability
The extent to which it is possible to halt processing due to incorrect use.
Source: QUINT
Scale: ratio
Validity: ***
Protocol:
1. Attempt to halt processing by incorrect use;
2. Register starting time of trials and the time at which processing is halted;
3. Determine the average amount of time per period.
Note: One could decide that this measurement should be carried out by experts.
3. integrity value
Estimate of the probability of a specified infringement within a certain period.
Source: QUINT
Scale: ratio
Validity: **
Protocol:
1. Estimate the probability that incorrect use of type i will occur (i.e. threat(i)) within a certain period;
2. Estimate the effectiveness of the security design decisions which should prevent incorrect use of type i. The estimate should be between 0 and 1 (i.e. security(i));
3. Calculate the probability of infringement (integrity) with the following formula:
Where i = type of infringement of incorrect use.
4. breakdown ratio
The ratio of number of observed breakdowns to the number of observed failures through a given period of time.
Source: ISO
Note: A lower value is preferred.
5. operational/input error detection ratio
The ratio of number of erroneous operations or inputs detected by a software system to the number of erroneous operations or inputs conducted during a given period of time.
Source: ISO
Note: A higher ratio is preferred.