Related characteristics
maturity
fault tolerance
recoverability
availability
degradability
Maturity
Description
Attributes of software that bear on the frequency of failure by faults in the software.
Indicators
1. mean time between failures (MTBF)
Average time that passes between two failures.
Source: QUINT
Scale: ratio
Validity: ***
Protocol:
1. Determine the relevant failures;
2. Determine how often or how long measurement should be carried out to ensure sufficiently reliable results;
3. Measure the interval between restart of the software product and a failure during this period/number of failures;
4. Average these interval lengths.
or, Protocol:
1. Determine the relevant failures;
2. Determine how often or how long measurement should take place to ensure a sufficiently reliable measurement, according to the Reliability Growth Model [MIO87];
3. Measure the interval between restart of the software product and a failure during this period/number of failures;
4. Analyse the failure and improve the software product until the requirements mentioned under (2) are satisfied.
Note: Prior to the development of the software product, the participants should agree on which failures are relevant. Relevance of a failure may depend on the subsystem in which it occurs, the occurrence of the failure or the consequences of a failure. Product development costs are reduced when highest maturity is only required for a specific part of the software product.
2. mean time to failure (MTTF)
The mean time between one failure occurrence and succeeding failure occurrence during a given period of time.
Source: ISO
Note: A higher value is preferred.
3. product fault density
The ratio of number of faults in a released product to the unit volume (e.g. pages, KLOC) of a released product (e.g. user documents, source code).
Source: ISO
Note: A lower value is preferred.
4. product stability
The ratio of faults corrected up to a point of time to the estimated number of faults initially present in a product.
Source: ISO
Note: A higher value is preferred.
5. fault density
The ratio of number of faults in a product to the unit volume of a product (e.g. design specification, functionality specification, source code).
Source: ISO
Note: A lower value is preferred.
6. test density
The ratio of test volume (e.g. number of test cases) conducted during the development phase to the unit volume of a product tested and released.
Source: ISO
Note: A higher value is preferred.
7. test coverage
The ratio of amount of tests actually carried out up to a point in time to the total amount of tests to be carried out.
Source: ISO
Note: A higher value is preferred.