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Metriche nel software

Metriche nel software. Luca Lista INFN, Sezione di Napoli. 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

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Metriche nel software

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

  2. 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 Luca Lista - C++

  3. 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] Luca Lista - C++

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

  5. …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 Luca Lista - C++

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

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