CODEWITHSUNDEEP
mysqldatabase-designer-modeling
장석인
장석인

Reputation: 5

how to determine weak and strong entity in ER model

ER modeling below situation

" a car insurance company whose customers own one or more cars each. Each car has associated with it zero to any number of recorded accidents. Each insurance policy covers one or more cars, and has one or more premium payments associated with it. Each payment is for a particular period of time, and has an associated due date, and the date when the payment was received"

the answer ER model

Above situation, First, I think 'car' is participated partially and 'accident' is participated totally. But the answer image is reversed. Also, I don't know WHY 'car' and 'accident' is not identifying relationship. I think accident is dependent on car.

Upvotes: 0

Views: 145

Answers (1)

Rick James
Rick James

Reputation: 142298

To heck with terminology; let's think about the data:

  1. Each Entity needs a table: Customers, Cars, Accidents, Policies, Premiums
  2. Determine the Relations, and whether they are 1:many or many:many
  3. Build a many:many table for each such Relation. (In some situations, extra data can be put in that table.) (You don't have such?)

Not needed: Customers (1:many) Cars -- because of Customers->Policys->Cars
Cars (1:many) Accidents (allowing zero takes no extra effort)
Customers (1:many??) Policies
Policies (1:many) Cars
Policies (1:many) Payments

  1. For the 1:many Relations, have the id of the "1" in the "many" table. Eg, PolicyId should be a column in the tables Cars and Payments.

Upvotes: 0

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