A Vehicle Manufacturer Database (Cont.)

Persons
This entity has a name, age and domicile, and possesses a private fleet.

Person
PersNo Name ...

Employees
It is with specific qualifications, salary, and family members.

Employee
EmplNo ...
SubsEmpl
CompanyID NameSubs Empl

The problems are require individual relation schemata equipped with special integrity constraints.

The Query Problem
Defining queries against this schema becomes complicated. For example, the following query is composed to know whether an employee named Pokemon is employed in the Detroit subsidiary of the Ford company: 

SELECT  EmplNo
  FROM  Company, Subsidiary, SubsEmpl, Employee
  WHERE  Company.Name = 'Ford'  AND
         Company.CompanyID = Subsidiary.CompanyID  AND
         Subsidiary.Location = 'Detroit'  AND
         Subsidiary.CompanyID = SubsEmpl.CompanyID  AND
         Subsidiary.NameSubs = SubsEmpl.NameSubs  AND
         SubsEmpl.Empl = Employee.EmplNo  AND
         Employee.Name = 'Pokemon';