# Re: header part of the value?

Date: Thu, 28 Feb 2008 08:27:53 -0800 (PST)

Message-ID: <ba7384a4-8823-49c1-bf58-fe556f38067b_at_x30g2000hsd.googlegroups.com>

On Feb 28, 12:03 am, Jan Hidders <hidd..._at_gmail.com> wrote:

> On 28 feb, 04:32, Tegiri Nenashi <TegiriNena..._at_gmail.com> wrote:

*>
**> > On Feb 27, 7:08 pm, Marshall <marshall.spi..._at_gmail.com> wrote:
**>
**> > > It appears to me as if you are viewing the
**> > > equation "x + 3 = y" as having 3 as the free variable, and
**> > > x and y as constants! Whereas I would consider it much
**> > > more natural to consider x and y as free variables, or
**> > > parameters, or attribute names (they are all the same)
**> > > and 3 and 5 as constants.
**>
**> > Well, the case with two variables in the header is tricky. First,
**> > define union and join then we can talk about it:-)
**>
**> How about: the union is the logical disjunction of the equations and
**> the join is the logical conjunction of the equations?
*

Can you please apply your definition on the example:

Q:

x + 3 = y \/

x + 5 = y

R:

x + y = 7

What is the header of the join, is it {"x+...=y", "x+y=7"}, or is it {"x=...", "y=..."}. What is the header of the union? Received on Thu Feb 28 2008 - 17:27:53 CET