Slide 15.3: Four major database research areas Slide 15.5: A vehicle manufacturer database (cont.) Home

A Vehicle Manufacturer Database

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These two slides show how to represent a vehicle manufacturer in the relational model and the problems with that model.

Companies
This entity has a name, head office, several subsidiaries, and a president.

Company CompanyID Name Street Location President

The problems with this representation are

• Compound attributes: For example, the head office can not be represented directly. Therefore, the head office must be eliminated and replaced by street and location.


• Set-valued attributes: For example, subsidiaries must be differentiated from single-valued ones and represented in a different relational schema.


• Artificial key: In order to establish a relationship between a company and its subsidiaries, an artificial key such as CompanyID will be necessary for obtaining a unique identification, because companies may carry the same company name in different countries.

Subsidiaries
It has a name, office, manager, and employees.

Subsidiary CompanyID NameSubs Street Location Manager

The set-valued attribute employees requires a third relational schema.

Slide 15.3: Four major database research areas Slide 15.5: A vehicle manufacturer database (cont.) Home

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