Developing an E-R Diagram

• Weak Entity

  • Put the key of the parent table (strong entity) in the weak entity.
  • The weak entity relationship conforms to the same rules as the 1:M relationship, except foreign key restrictions:
    NOT NULL
    
    ON DELETE CASCADE
    ON UPDATE CASCADE

• M:N Relationship

  • Convert the M:N relationship to a composite (bridge) entity consisting of (at least) the parent tables’ primary keys.

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