Re: what are keys and surrogates?

vldm10 wrote:

>Definition1 A function from A to B is a rule that assigns, to each
>member of set A, exactly one member of set B.
>
>Is this good or bad definition for a function?

It's good in that it states what we often informally mean by "function".

It's bad in that it isn't formal, and therefore, not exact; what is a rule? A more serious problem is that it doesn't correspond to what mathematicians mean by a function, namely, an assignment to each member of a set A of exactly one member of a set B. The difference becomes clear when you ask on which grounds two functions are considered to be the same function. Finally, it doesn't mention that many authors use the term "function" for a partial function, i.e. an assignment to 0 or more members of set A.

-- 
Reinier