1. Luca Lista - C++ Metriche nel software Luca Lista INFN, Sezione di Napoli

2. Luca Lista - C++ The Dependency Metrics [1] Responsibility, Independence and Stability of a Package –Ca: Afferent Couplings # of dependent external classes –Ce: Efferent Couplings # internal classes dependent on external –Instability: Ce / (Ca+Ce) [0,1] 0 = maximally independent 1 = dependent but with no dependents [1] R.Martin, www.oma.com

3. Luca Lista - C++ Stability vs. Flexibility Open Closed Principle –Stable (good) Package Responsible independent abstract classes –Unstable (good) Package Dependent irresponsible concrete classes Abstractness –# abstract classes / total # of classes [0,1]

4. Luca Lista - C++ The Main Sequence Define Stability-Abstractness relationship Main Sequence (0,1) (1,0) Maximally stable & abstract Maximally unstable & concrete

5. Luca Lista - C++ …and its statement The MS textual definition –Packages that are maximally stable should be maximally abstract. Instable packages should be concrete. The abstraction of a package should be in proportion to its stability Combined with the Stable Dependencies –Dependency Inversion Principle for classes dependencies toward abstractions

6. Luca Lista - C++ Example of metrics Main Sequence IfrGeomBase IfrData IfrPidData IfrDataImp IfrGeom IfrGeomP IfrReco IfrSequence IfrDataP IfrEnv IfrSim IfrPid IfrVisitors 0 10 20 30 40 50 60 70 80 90 100 0102030405060708090100 Instability Abstractness