The wonderful world of keys

Would one be correct in saying that "a key represents the set of antecedents of the material implication in a relation's predicate?".

I have always considered keys in terms of functional dependencies/determinants, and was trying to reword it in the terminology of logic. I liked the idea of describing a key using "if then" to explain why there cannot be any other consequent values, and so why (logically) the column has to be a unique, because I could then analogise to java students (who always have trouble with this sort of thing) why its nonsensical to have duplicate key values with a bit of code like:

switch (empID)
{
  case 1: salary = 20000; break;
  case 1: salary = 30000; break;
}

But on considering the possibility of a relation having a superkey which includes all its attributes, and hence where there is no material implication at all in its describing predicate, I ran into a bit of a mental block. Perhaps my analogy is awry, I'm not certain, as I seem then to be saying in this case that there is nothing on the other side of the -> implication, other than a 'true'. Perhaps this is ok? Thoughts welcome. Received on Wed Jan 24 2007 - 17:59:58 CET