Entity Relationship Diagram

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Entity Relationship Diagram#

In an entity relationship diagram (ERD), we have the following objects:

  • Relations (diamond)

    • Attributes

  • Entity (circle)

    • Attributes

    • Primary key

  • Relationships (line connectors or cardinality)

Cardinality#

One : Test

Many : Test

One (and only one) : Entity is related to only one of the other entity.

$$ F(x) \neq G(y) \quad x \neq  y $$

Zero or one : Entity is related to one or none of the other entity.

One or many : Entity is related to at least one of the other entity.

Zero or many : Entity is related to a nonnegative number of the other entity.

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