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When a ternary relationship
occurs in an ER model they should always be removed before finishing the model.
Sometimes the relationships can be replaced by a series of binary relationships
that link pairs of the original ternary relationship.
This can result in the loss of
some information - It is no longer clear which sales assistant sold a customer
a particular product.
Try replacing the ternary
relationship with an entity type and a set of binary relationships.
Relationships are usually verbs,
so name the new entity type by the relationship verb rewritten as a noun.
The relationship sells can become the entity
type sale.
So a sales assistant can be
linked to a specific customer and both of them to the sale of a particular
product.
This process also works for higher order
relationships.
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