Concern-oriented heuristic assessment of design stability

ControllerIControllerPhotoController CoreController SMSController Chain of Responsibility Application DomainProperties Figure 2-3: Distribution Map showing the Chain of Responsibility property Based on this representation of the system, four concern metrics were proposed byDucasse, Girba, and Kuhn [41], namely Size, Touch, Spread, and Focus. The Sizemetric counts the number of small squares associated with a property. The Touchmetric counts the relative size given in terms of the percentage of small squaresrealising a property. For instance, Figure 2-3 shows that the Size value of Chain ofResponsibility is nine and the Touch value is 0.23 (9/39). Spread counts the number ofpartitions that contains shadowed squares. Note that, in our running example (Figures2-1 and 2-3), Spread gives the same result (five) as the CDC metric proposed bySant’Anna [134]. Finally, the Focus metric quantifies the closeness between aparticular partition and the property. In other words, the larger the Focus value is, themore parts touched by the property are touched entirely by it. This means that well-encapsulated concerns have a high Focus value whereas crosscutting concerns have alow value. The Focus value of the Chain of Responsibility design pattern is 0.39 inFigure 2-3.