Software package metrics
Encyclopedia
This article describes various software package
metric
s. They have been mentioned by Robert Cecil Martin
in his Agile Software Development: Principles, Patterns, and Practices book (2002).
The term software package, as it is used here, refers to a group of related class
es (in the field of object-oriented programming
).
Modular programming
Modular programming is a software design technique that increases the extent to which software is composed of separate, interchangeable components called modules by breaking down program functions into modules, each of which accomplishes one function and contains everything necessary to accomplish...
metric
Software metric
A software metric is a measure of some property of a piece of software or its specifications. Since quantitative measurements are essential in all sciences, there is a continuous effort by computer science practitioners and theoreticians to bring similar approaches to software development...
s. They have been mentioned by Robert Cecil Martin
Robert Cecil Martin
Robert Cecil Martin, known colloquially as "Uncle Bob", is an American software consultant and author. Martin has been a software professional since 1970 and an international software consultant since 1990. In 2001, he initiated the meeting of the group that created Agile software development from...
in his Agile Software Development: Principles, Patterns, and Practices book (2002).
The term software package, as it is used here, refers to a group of related class
Class (computer science)
In object-oriented programming, a class is a construct that is used as a blueprint to create instances of itself – referred to as class instances, class objects, instance objects or simply objects. A class defines constituent members which enable these class instances to have state and behavior...
es (in the field of object-oriented programming
Object-oriented programming
Object-oriented programming is a programming paradigm using "objects" – data structures consisting of data fields and methods together with their interactions – to design applications and computer programs. Programming techniques may include features such as data abstraction,...
).
- Number of Classes and Interfaces: The number of concrete and abstract classes (and interfaces) in the package is an indicator of the extensibility of the package.
- Afferent CouplingCoupling (computer science)In computer science, coupling or dependency is the degree to which each program module relies on each one of the other modules.Coupling is usually contrasted with cohesion. Low coupling often correlates with high cohesion, and vice versa...
s (Ca): The number of other packages that depend upon classes within the package is an indicator of the package's responsibility. - Efferent Couplings (Ce)Efferent CouplingEfferent Coupling is a metric in software development. It measures the number of data types a class knows about.This includes inheritance, interface implementation, parameter types, variable types, and exceptions....
: The number of other packages that the classes in the package depend upon is an indicator of the package's independence. - Abstractness (A): The ratio of the number of abstract classes (and interfaces) in the analyzed package to the total number of classes in the analyzed package. The range for this metric is 0 to 1, with A=0 indicating a completely concrete package and A=1 indicating a completely abstract package.
- Instability (I): The ratio of efferent coupling (Ce) to total coupling (Ce + Ca) such that I = Ce / (Ce + Ca). This metric is an indicator of the package's resilience to change. The range for this metric is 0 to 1, with I=0 indicating a completely stable package and I=1 indicating a completely instable package.
- Distance from the Main Sequence (D): The perpendicular distance of a package from the idealized line A + I = 1. This metric is an indicator of the package's balance between abstractness and stability. A package squarely on the main sequence is optimally balanced with respect to its abstractness and stability. Ideal packages are either completely abstract and stable (x=0, y=1) or completely concrete and instable (x=1, y=0). The range for this metric is 0 to 1, with D=0 indicating a package that is coincident with the main sequence and D=1 indicating a package that is as far from the main sequence as possible.
- Package Dependency Cycles: Package dependency cycles are reported along with the hierarchical paths of packages participating in package dependency cycles.
See also
- Inversion of ControlInversion of ControlIn software engineering, Inversion of Control is an abstract principle describing an aspect of some software architecture designs in which the flow of control of a system is inverted in comparison to procedural programming....
– a method to reduce coupling, also known as the "Dependency Inversion Principle" (Martin 2002:127).
External links
- OO Metrics tutorial explains package metrics with examples