# Re: Character string relation and functional dependencies

Date: Tue, 11 Dec 2007 09:20:39 -0800 (PST)

Message-ID: <f7283774-a81f-417a-9942-ca25012ff6d3_at_i29g2000prf.googlegroups.com>

On Dec 11, 6:08 am, "V.J. Kumar" <vjkm..._at_gmail.com> wrote:

> The formulas look very cute, no doubt about that, but immediate questions

*> are:
**>
**> how do you propose to index infinite relations ?
*

First, let's establish the idea that an index for a finite relation R(x,y) is a function. Given x=1 an index function returns all the "matching" tuples, or a single tuple if there is a functional dependency x->y. For an equality relation x=y this function is identity: given x, return x.

> what do you do when you join two infinite relations and the result is also

*> an infinite relation: x < 5 join x > 1 where x ranges over reals ?
*

Well, let's not get into incountable domains, because there appeared no way to apply the ideas of pipelined execution flow there. Also, as Marshal noted, it is perfectly allright for an intermediatory query evaluation result to be infinite; it is the final result where a user is expected to see the finite set. Received on Tue Dec 11 2007 - 18:20:39 CET