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UML and Data Modeling: A Reconciliation by David Hay

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Both entity/relationship modeling and UML object-oriented modeling recognize that attributes and relationships are both properties of an entity class. In entity/relationship notations, maximum and minimum cardinality are represented differently for attributes and relationships. In UML, the same approach is taken for all properties.

In the Information Engineering notation, minimum cardinality in relationships is shown by either a circle (o) for optional, or a vertical line (|) for mandatory—both next to the second entity class. Maximum cardinality is shown by a second vertical line (|) next to the maximum.

The Barker-Ellis notation shows minimum cardinality by the half line closest to the first entity class. If it is solid, ...

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