# Re: more on delete from join

From: Vadim Tropashko <vadimtro_at_gmail.com>

Date: Tue, 1 Sep 2009 11:15:04 -0700 (PDT)

Message-ID: <e60aec47-04b2-47f1-943e-f9a5c882816a_at_13g2000prl.googlegroups.com>

On Aug 31, 9:59 am, "Walter Mitty" <wami..._at_verizon.net> wrote:

Date: Tue, 1 Sep 2009 11:15:04 -0700 (PDT)

Message-ID: <e60aec47-04b2-47f1-943e-f9a5c882816a_at_13g2000prl.googlegroups.com>

On Aug 31, 9:59 am, "Walter Mitty" <wami..._at_verizon.net> wrote:

*> ... Is the same as a relation on x and y such that the equation is true. Of**> course if x and y are defined as integers, this will give a different**> relation than if x and y are defined as reals (or some finite subset of**> reals) so a system of equations is a special case of a system of**> relations.**>**> x + y = 8**> x - y = 2**>**> Is a system of equations and therefore a system or relations. Now the**> intersection of thses two relations is the single point, (5, 3) or, if you**> prefer (x=5, y=3).**> Solving the system boils down to finding the intersection of two relations.**> A system of equations can be overconstrained, and have no solutions (the**> intersection is the empty set) or underconstrained**> (the intersection is a set with many elements).**>**> Now if we switch over to**>*

*> A JOIN B = C**> ...*Well the analogy with linear system of equations

x + y = 8

x - y = 2

can be extended a little more. If (natural) join is analogus to '+' then (inner) union is somewhat analogos to minus. Perhaps we can update a system of views that consisting of join and union viewes?

OK, here is a simpler question: is the system

x v y = u

x ^ y = w

underconstrained, or it could be solved in terms of x and y

x = f(u,w)

y = g(u,w)

? One of the basic RL results is that it is undeconstrained! Received on Tue Sep 01 2009 - 13:15:04 CDT