ScalarInh Metrics

The ScalarInh metrics provide measurements relating to an individual module's participation in inheritance. (For measurements relating to inheritance over the whole system see the SummaryInh metrics suite.) These are based on the original DIT and NOC metrics proposed by Chidamber and Kemerer (CK). The model on which these metrics are based is a graph with modules as vertices and different kinds of edges between them indicating their inheritance relationships. CC edges connect two classes (ie extends), CI connect a class with an interface (implements), and II connect two interfaces (extends). Standard graph metrics such as in- or out-degree, path length, and subgraph size can be restricted to kind of each or characteristic of paths. This gives various classes of metrics, such as depth in inheritance tree (DIT), number of children (NOC), number of ancestors (NOA), number of descendants (NOD), and number of parents (NOP).

DITCCUD

Length of path from a class and consisting only of extends edges to the first non user-defined class other than Object, or one less than the length of the path that ends with Object.

DITIIUD

Length of path from an interface and consisting only of extends edges to the first non user-defined class.

NOACC

Number of ancestors a class has (extends edges only)

NOAII

Number of ancestors an interface has (extends edges only)

NOAALL

Number of all ancestors a type has (both implements and extends edges).

NOCCC

Number of classes inheriting from a given class (via extends edges).

NOCIC

Number of classes implementing a given interface (via implements edges).

NOCII

Number of interfaces inheriting from a given interface (via extends edges).

NOCI

Total number of classes that implement a given interface and interfaces that extend that interface (both implements and extends edges).

NODCC

Number of descendants a class has (extends edges only)

NODII

Number of descendants an interface has (implements edges only)

NODALL

Number of all descendants a type has (both implements and extends edges).

NOPCI

Number of interface parents a class has (via implements edges)

NOPC

Number of parents a class has (both classes and interfaces).

NOPI

Number of parents an interface has (via extends edges).

Further Information

• Full definitions and an empirical study using these metrics on various Java open source systems can be found in:

  Ewan Tempero, James Noble and Hayden Melton 'How do Java Programs Use Inheritance? An Empirical Study of Inheritance in Java Software' 22nd European Conference on Object-Oriented Programming (ECOOP), Springer Berlin / Heidelberg Paphos, Cyprus. July 2008. pp. 667-691. [Publisher] [Earlier TR]

• The original DIT and NOC proposals:

  Chidamber, S. R. and Kemerer, C. F. Towards a metrics suite for object oriented design. In Conference Proceedings on Object-Oriented Programming Systems, Languages, and Applications (Phoenix, Arizona, United States, October 06 - 11, 1991). A. Paepcke, Ed. OOPSLA '91. ACM Press, New York, NY, 197-211. [DOI]