Re: Basic question?What 's the key if there 's no FD(Functional Dependencies)?

I used here the terms "entity" and "attribute" and they are related to the real world.
I am always starting from the real world to RM. Often the term "attribute" is used when we are speaking about some relation.
In this manner, sometime there is a try to mix somehow the real attributes, their values,
a concept, a property, a column... as one thing. The attributes are not defined in RM.
Some authors emphasizes that "attribute" is synonym for "column" in the
RM and this is OK.
So I didn't speak about the columns, I spoke about real attributes. I gave the example to test above relation. To clarify my example, let entity be a car, and let A,B,C is respectively
Color, Type_Of_Wiper, Type_of_Brake.
Let 2 be white color and 8 is for blue color.

Later you can try to analyze the relation just with last two rows from my example
and the attributes whose (all) values can be changed. We assume ABC is "natural" key.
And they are good solutions with different kind of the key, which work. Received on Thu Nov 02 2006 - 08:00:34 CET