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Cardinalities

# Cardinalities - Cardinalities Cardinalities are easiest if...

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Cardinalities Cardinalities are easiest if you do them one entity at a time. A B

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Start with the left-hand entity Cover up the other entity. A B (     ,     )
Do the minimum cardinality first Does each instance participate? yes=1, no=0 A B ( ?   ,     ) (0 ,     )

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Then do the maximum cardinality Does any instance correspond to more than 1? yes=N, no=1 A B (0 ,     ) (0 , 1)
(0 , 1) Now do the right-hand entity Cover up the other entity A B

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Do the minimum cardinality first Does each instance participate? yes=1, no=0 A B ( ?   ,     ) (0 ,     )
Then do the maximum cardinality Does an instance correspond to more than 1? yes=N, no=1 A B (0 ,     ) (0 , 1)

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And voila! A B (0 , 1) (0 , 1)
Another example A B

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A B ( ?   ,     ) (0 ,     ) (0 , N)
A B ( ?   ,     ) (1 ,  ?  ) (1 , 1)

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A B (0 , N) (1 , 1)
TYPE peanut butter & jelly BLT peanut butter & banana INGREDIENTS SANDWICH INGREDIENT bread peanut butter jelly bacon lettuce banana (1 , N) (1 , N)

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• Spring '08
• scrowley
• Academy Award for Best Actor, Star Wars, Al Pacino, Star Wars Episode I: The Phantom Menace, Intermediate Acct II

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Cardinalities - Cardinalities Cardinalities are easiest if...

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