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occurrence
subject			fact

occurrence	has definition An object that is a member of a set of classes that set share common information but also differ from each other in important ways
	has example a member of the set of all episodes of a television series - they have the same producer and the same series title, but different story-lines.
	is a subtopic of 6.2 - The Abstraction-Occurrence Pattern
	is a kind of object
object	can be referred to without reference to the data (instance variables) contained in it
	can be referred to by several different variables at the same time
	can represent any entity to which you can associate properties and behaviour
	has live activation while the object is performing computations in a sequence diagram
	has behaviour
	has state
	has synonym instance: instance is used when you are talking about the role with respect to the class and object is used when talking in a more general way
	is distinct from every other object even if they contain the same data
	is in a state until an event occurs that causes it to change state
	is structured
	is drawn as a rectangle containing a colon and the underlined name of the class (optional if it is clear from the context), which may be preceded by an optional instance name in a UML instance diagram