Re: Database design, Keys and some other things

vldm10 wrote:
> Here is a simple example about two entities and one relationship - Car,
> Person and Owner. It tries to describe more realistically Real World
> situations. A car had its color changed twice. In the Real World
> attributes are often changed. In another entity, the person Mary
> changed her last name because she got married. In the relationship
> Owner it can happen that one person buys the same car twice during a
> period of time. It can also happen that two entities can be in the same
> relationship many times. So,I believe that this new approach is more
> appropriate.
>
> Given the table Car :
> CarKey CarID Make Color ...
> ______________________________________________________
> ...
> 23 vin1 Buick silver ...
> 24 vin1 Buick blue ...
> 25 vin1 Buick red ...
> 26 vin2 Honda silver ...
> 27 vin3 Ford black ...
> ...
>
> In the Car table VIN = Vehicle Identification Number

What kind of facts do you have in this table? What does one row mean?

The ... needs some date/interval columns to make any sense out of this table.

I don't see "CarKey" as a car identifier here - it may identify something, but not a car.

> Now, let Person be the following table:
> PersonKey PersonID PersonName ...
> _______________________________________________________
> ...
> 208 ssn1 Mary Jones ...
> 209 ssn1 Mary Adams ...
> 210 ssn2 John Stewart ...
> ...
>
> In the Person table SSN = Social Security Number

m.m. same here.

[snip combination] Received on Fri Sep 23 2005 - 20:21:05 CEST