# Measurements and metrics

The metrics and composite measurements that are capabable to evaluate different facets of a feature model (FM):

- FM name
- the total number of features
- the number of mandatory features
- the number of optional features
- the number of dead features
- the number of leaves, i.e. features with no children or further specialization
- depth of tree, i.e. the length of the longest path from the FM root to leaf features
- the total number of FM edges
- the number of 'mandatory' edges, i.e. edges that define mandatory features with their parents
- the number of 'optional' edges, i.e. edges that define optional features with their parents
- the total number of FM groups
- the number of FM mutex-groups
- the number of FM or-groups
- the number of FM xor-groups
- the total number of FM constraints
- the number of FM 'imply' constraints
- the number of FM 'bi-imply' constraints
- the number of FM 'exclude' constraints
- the number of valid FM configurations
- cross-tree constraints, i.e. the ratio of the number of unique features involved in the FM constraints over the number of all FM features
- ratio of variability for n-th layer features, i.e. the average number of children of the n-th layer nodes (root feature - 0 layer)
- the number of n-th layer nodes
- flexibility of configuration, i.e. the ratio of the number of optional features over the total number of FM features
- variability rate, i.e. the ratio of features that add variability to a FM (optional features and groups' constituents) over the total fetures number