Relationship To Aspect-oriented Programming
The introduction of aspect-oriented programming in 1997, raised questions about its relationship to subject-oriented programming, and about the difference between subjects and aspects. These questions were unanswered for some time, but were addressed in the patent on Aspect-oriented programming filed in 1999 in which two points emerge as characteristic differences from earlier art:
- the aspect program comprises both a) a cross-cut that comprises a point in the execution where cross-cutting behavior is to be included; and b) a cross-cut action comprising a piece of implementation associated with the cross-cut, the piece of implementation comprising computer readable program code that implements the cross-cutting behavior.
- the aspect transparently forces the cross-cutting behavior on object classes and other software entities
In the subject-oriented view, the cross-cut may be placed separately from the aspect (subject) and the behavior is not forced by the aspect, but governed by rules of composition. Hindsight makes it also possible to distinguish aspect-oriented programming by its introduction and exploitation of the concept of a query-like pointcut to externally impose the join-points used by aspects in general ways.
In the presentation of subject-oriented programming, the join-points were deliberately restricted to field access and method call on the grounds that those were the points at which well-designed frameworks were designed to admit functional extension. The use of externally imposed pointcuts is an important linguistic capability, but remains one of the most controversial features of aspect-oriented programming.
Read more about this topic: Subject-oriented Programming
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