The introduction of [[aspect-oriented programming]] in 1997<ref>{{citeCite conference doi| doi = 10.1007/BFb0053381| title = Aspect-oriented programming| work = Proceedings of the 11th European Conference on Object-Oriented Programming| conference = [[European Conference on Object-Oriented Programming|ECOOP]]'97| volume = 1241| pages = 220–242| series = [[Lecture Notes in Computer Science|LNCS]]| year = 1997| last1 = Kiczales | first1 = G. | author1-link = Gregor Kiczales | last2 = Lamping | first2 = J. | last3 = Mendhekar | first3 = A. | last4 = Maeda | first4 = C. | last5 = Lopes | first5 = C. | last6 = Loingtier | first6 = J. M. | last7 = Irwin | first7 = J. | isbn = 3-540-63089-9| id = {{citeseerx|10.1.1.115.8660}}| url = http://www.cs.ubc.ca/~gregor/papers/kiczales-ECOOP1997-AOP.pdf}}</ref> 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<ref>Kiczales; Gregor J.; Lamping; John O.; Lopes; Cristina V.; Hugunin; James J.; Hilsdale; Erik A.; Boyapati; Chandrasekhar, Aspect Oriented Programming, United States Patent 6,467,086, October 15, 2002</ref> 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
