Cardinality

Updated 06 Sep 2026

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def
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  the specification of the number of occurrences of one object that can be related to the number of occurrences of another object in a given relationship
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values
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  usually expressed as "one" or "many"
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cardinality types
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  1:1 — one object can relate to only one other object
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  1:M — one object can relate to many objects
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  M:N — some number of occurrences of one object can relate to some number of occurrences of another
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note
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  cardinality alone does not indicate whether participation in a relationship is mandatory or optional — see Modality
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related
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Cards
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  Distinguish cardinality from modality.
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    cardinality: the maximum number of related instances (1:1, 1:M, M:N); modality: whether the relationship is mandatory or optional (minimum 0 or 1)

Linked references 4