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Unit 1: Database System Architecture

202114m

Construct an E-R diagram for a car insurance company that has a set of customers, each of whom owns one or more cars. Each car has associated with it zero to any number of recorded accidents..

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E-R Diagram for Car Insurance Company:

Entities:

  • Customer (attributes: cust_id PK, name, address, phone)
  • Car (attributes: car_id PK, model, year, color, reg_no)
  • Accident (attributes: acc_id PK, date, location, damage_amount) - weak or regular, depends on design; accident identified by car + date.

Relationships:

  • Owns: Customer (1) -- (N) Car, total participation on Car side (each car owned by one customer), cardinality one-to-many, key of Customer included in Car as foreign key if mapped.
  • Involved/Has: Car (1) -- (N) Accident, zero to many (0..*), each car may have zero or many accidents, each accident belongs to one car. Accident could be weak entity with Car as owner, partial key acc_id or date.

If accident is weak: Car --< Accident (double diamond), accident PK = car_id + acc_no.

Constraints: Customer owns at least one car, Car owned by exactly one Customer, Accident associated with exactly one Car.

Diagram: Rectangles for Customer, Car, Accident; Diamonds for Owns and Had; Lines with cardinalities (1:N). Show primary keys underlined, weak entity double rectangle, identifying relationship double diamond. No image URL required - textual description suffices for construction.

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