Related characteristics

maturity
fault tolerance
recoverability
availability
degradability

Availability

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Description

Attributes of software that bear on the amount of time the product is available to the user at the time it is needed.

Indicators

1. full-time availability ratio

The ratio of time in which the software product is not in recovery during a certain period.

Source: QUINT

Scale: ratio

Validity: ***

Protocol:

1. Measure the Mean Time Between Failures (MTBF), an indicator for maturity;
2. Measure the Mean Time To Repair (MTTR), an indicator for recoverability;
3. Calculate the full-time availability, which is MTBF / (MTBF + MTTR).

Note: This indicator is only valid for systems where full-time availability is desirable. Otherwise the recovery can take place when the system is not required to be available.

2. relative availability ratio

The ratio of time the software product is available to the time it is needed.

Source: QUINT

Scale: ratio

Validity: ***

Protocol:

1. Determine the period in which availability will be measured;
2. Determine the desired availability of the software product during this period;
3. Determine the actual availability of the software product during this period;
4. Calculate the relative availability, which is (3) / (2).

Note: This indicator differs from the full-time availability ratio when full-time availability is not required and recovery can take place when the system is not needed to be available.

3. availability ratio

The ratio of total operating time of software system to the total observation time.

Source: ISO

Note: A higher value is preferred.