6.8 Maintainability measures

What this heading covers

These are inherent measures. They read the product as built, not as used, and most of them can be collected from the repository, the build and the test suite. Modularity is about the separation of parts. Reusability is about whether an asset can be used in another context. Analysability is about the effort to diagnose a defect or a change. Modifiability is about the effort to change it. Testability is about the effort to test it. The draft gives each its own family because they fail separately: a modular product can be hard to analyse, and an analysable product can be hard to test. The measures are proxies for effort, and the draft does not set target values, so the baseline and the trend carry the meaning.

Record position: characteristic 7 of 9, carrying 5 of the 40 measure families in clause 6.

What the heading asks of a team

The common confusion

Maintainability is often reported as code complexity. The five families are about effort: to analyse, to change, to test and to reuse. A structural count is a proxy that has to be validated against that effort.

The measure families in this characteristic

• 6.8.2 Modularity measures
• 6.8.3 Reusability measures
• 6.8.4 Analysability measures
• 6.8.5 Modifiability measures
• 6.8.6 Testability measures

What to put in place before publication

1. Choose the repository and build data sources for each of the five families, and record their coverage.
2. Define the change and defect populations the analysability and modifiability measures use.
3. Record a baseline for each measure before any refactoring, so the trend has a starting point.
4. Validate at least one structural proxy against observed effort, and record the correlation or its absence.
5. Keep the measures out of individual performance review, because they are properties of the product.

Where teams usually fall short

• A cyclomatic complexity average presented as maintainability, with no link to change effort.
• Measures collected once at the start of a programme and never again, so there is no trend.

What happens next

Analysability, modifiability and testability are the three that a delivery team feels. Modularity and reusability are the two that a platform owner asks about.