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abstraction-occurrence
subject			fact

abstraction-occurrence	has definition A pattern in which two classes are related by an association, and one of the classes represents an abstraction of the other
	has antipatterns using a single class creating a separate abstraction subclass for each occurrence making the abstraction class a superclass of the occurrence class
	has context class diagrams that form part of a system domain model
	has forces You want to represent the members of each set of occurrences without duplicating the common information You want a solution that maximizes the flexibility of the system
	has problem What is the best way to represent sets of occurrences in a class diagram?
	has references a generalization of the Title-Item pattern of Eriksson and Penker
	has related patterns Abstraction-Occurrence Square pattern if the abstraction is an aggregate (and the occurrences are also aggregates)
	has solution Create an «Abstraction» class that contains the data that is common to all the members of a set of occurrences. Then create an «Occurrence» class representing the occurrences of this abstraction. Connect these classes with a one-to-many association
	is a subtopic of 6.2 - The Abstraction-Occurrence Pattern
	is an instance of design pattern
design pattern	has name
	should be illustrated using a simple diagram
	should be written using a narrative writing style
pattern	should be as general as possible
	should be described in an easy-to-understand form so that people can determine when and how to use it
	should contain a solution that has been proven to effectively solve the problem in the indicated context

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