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Unformatted text preview: can RELATIONSHIP at most how many instances of ENTITY2's • Or: each CUSTOMER can ORDER • Exercises o Order - has - item • You can have multiple items on one order • A bag of flour can be on more than one order (a vehicle by vin # could not be on more than one order however o Item - supplied by - supplier • What's the problem with M:M relationships? o Really confusing! o Create a linking table • Always use singular when naming a table and working with these. Mapping o Sequence • Map entities • Map relationships 1:M 1:1 M:M o For 1:M • The primary key in the 1 side becomes the foreign key on the many side o For 1:1 • Check to see if there's an optional side • The primary key on the required side becomes the foreign key in the optional side...
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- Winter '09
- Entity-relationship model, Supplier supplies item, Customer orders Order, ER Diagrams help