- Connascent software components
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Two software components are connascent if a change in one would require the other to be modified in order to maintain the overall correctness of the system. Connascence is a way to characterize and reason about certain types of complexity in software systems.
Contents
Strength
A form of connascence is considered to be stronger if it is more likely to require compensating changes in connascent elements. The stronger the form of connascence, the more difficult, and costly, it is to change the elements in the relationship.
Degree
The acceptability of connascence is related to the degree of its occurrence. Connascence might be acceptable in limited degree but unacceptable in large degree. For example, a function or method that takes two arguments is generally considered acceptable. However it is usually unacceptable for functions or methods to take ten arguments. Elements with a high degree of connascence incur greater difficulty, and cost, of change than elements that have a lower degree.
Locality
Locality matters when analyzing connascence. Stronger forms of connascence are acceptable if the elements involved are closely related. For example, many languages use positional arguments when calling functions or methods. This connascence of position is acceptable due the closeness of caller and callee. Passing arguments to a [web service] positionally is unacceptable due to the relative unrelatedness of the parties. The same strength and degree of connascence will have a higher difficulty, and cost, of change the less closely related the involved elements are.
Types of connascence
This is a list of some types of connascence ordered approximately from weak to strong forms
- Connascence of Name
- Connascence of name is when multiple components must agree on the name of an entity.
- Connascence of Type
- Connascence of type is when multiple components must agree on the type of an entity.
- Connascence of Meaning
- Connascence of meaning is when multiple components must agree on the meaning particular values.
- Connascence of Position
- Connascence of positions is when multiple components must agree on the order of values.
- Connascence of Algorithm
- Connascence of algorithm is when multiple components must agree on a particular algorithm.
- Connascence of Execution (order)
- Connascence of execution is when the order of execution of multiple components is important.
- Connascence of Timing
- Connascence of timing is when the timing of the execution of multiple components is important.
- Connascence of Identity
- Connascence of identity is when multiple components must reference the entity.
Reducing connascence
Reducing connascence will reduce the cost of change for a software system. One way of reducing connascence is by transforming strong forms of connascence into weaker forms. For example, a method that takes several arguments could be changed to use named parameters. This would change the connascence from position to name. Reducing the degree and increasing locality of involved elements are other ways to reduce connascence.
See also
References
- Meilir Page-Jones, Comparing techniques by means of encapsulation and connascence, Communications of the ACM, Volume 35, Issue 9
- What Every Programmer Should Know About Object Oriented Design, Meilir Page-Jones, Dorset House Publishing, ISBN 0-932633-31-5
- Fundamentals of Object-Oriented Design in UML, Meilir Page-Jones, Addison-Wesley Pub Co; ISBN 020169946X
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