Related characteristics

analysability
changeability
stability
testability
manageability
reusability

Changeability

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Description

Attributes of software that bear on the effort needed for modification, fault removal or for environmental change.

Indicators

1. modification effort per unit volume

Average amount of effort needed to modify the software product, per unit volume of the modification.

Source: QUINT Scale: ratio

Validity: **

Protocol:

1. Measure the effort needed to analyse the modification;
2. Measure the effort needed to modify the design;
3. Measure the effort needed to modify the software product;
4. Measure the effort needed to test the modification;
5. Measure the effort needed to implement the modified software product;
6. Determine the extent of the modification;
7. Calculate the modification effort per unit volume, which is the sum of the efforts/extent of modification.

Note: This measurement protocol requires considerable effort when fictional changes are proposed to test changeability.

2. correction effort per defect

Mean effort needed to repair a defect in the software product.

Source: QUINT

Scale: ratio Validity: **

Protocol:

1. Measure the effort needed to find the cause of the defect;
2. Measure the effort needed to correct the design;
3. Measure the effort needed to correct the software product;
4. Measure the effort needed to test the correction;
5. Measure the effort needed to implement the corrected product;
6. Calculate the correction effort, which is the sum of 1, 2, 3, 4 and 5;
7. Measure the correction effort for all defects during a set period;
8. Calculate the correction effort per defect, which is the sum of the correction efforts divided by the number of defects.

Note: This indicator can only be measured when testing the software product. However, by first developing a representative part of the product, the effects of the design decisions can be measured early. Objectivity is influenced by the possibility to divide the defect into more smaller defects, thus lowering the correction effort per defect. Criteria for the size of a defect have to be determined.

3. mean fault correction time

Mean time from receiving the failure report to sending the corrected software in fault correction.

Source: ISO

Note: A lower value is preferred.

4. mean failure treatment time

Mean time from the failure occurrence to the restoration for end users.

Source: ISO

Note: Failure treatment means problem resolution which includes finding and correcting faults arising from failures, or to provide an alternative operation procedures to avoid failures.

5. mean fault correction work time

Mean work time for correcting the discovered software fault to be corrected in fault correction, in consequence of analysing the failure.

Source: ISO

Note: This is a simplified version of 2. correction effort per defect.

6. mean revise work time per changed line of source code

Mean work time for revision per updated and added source code line.

Source: ISO

Note: This is a simplified version of 1. modification effort per unit volume.

7. fulfilment degree of maintenance document

Fulfilment degree of product documents that are usable in the maintenance stage.

Source: ISO

Note: This can be expressed in a ratio of number of document pages for maintenance divided by the number of lines of source code. A higher value is preferred.