Database design, Keys and some other things
Date: 23 Sep 2005 06:36:41 -0700
Message-ID: <1127482601.079853.35050_at_f14g2000cwb.googlegroups.com>
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
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
Then the relationship Owner, which is the act of owning a car, can have
the following
values:
OwnerKey Person Key CarKey Year ...
...
54 210 26 2003 ... 55 210 24 2004 ... 56 210 26 2005 ...
...
More details about this example can be found on my website
www.dbdesign10.com
where I gave a new definition of Key and tried to develop a new Data
Model.
Any feedback is greatly appreciated.
Vladimir Odrljin Received on Fri Sep 23 2005 - 15:36:41 CEST