1. Metrics

2. Basili’s work Basili et al., A Validation of Object- Oriented Design Metrics As Quality Indicators, IEEE TSE Vol. 22, No. 10, Oct. 96 Predictors of fault-prone classes? 8 medium sized information management systems

3. Metric CBO metric: coupling between object classes: a class is coupled to another one if it uses its member functions and/or instance variables. CBO = number of classes to which a given class is coupled.

4. Hypothesis H-CBO: Highly coupled classes are more fault-prone than weakly coupled classes.

5. Result Indeed, highly coupled classes are more fault-prone than weakly coupled classes. –Corollary: Classes that follow the LoD are less coupled and are therefore less fault-prone.

6. Demeter Motivation V. Basili 1996: classes with less coupling are less error prone. Demeter reduces the coupling in two stages: –Following the Law of Demeter using standard object-oriented techniques eliminates the obviously bad coupling. –Traversal strategies reduce the coupling further by coupling only with (distant) stable friends.