Re: header part of the value?

From: Jan Hidders <hidders_at_gmail.com>
Date: Thu, 28 Feb 2008 13:06:28 -0800 (PST)
Message-ID: <5dcfe1a9-3517-4315-8e27-cd7b5ba04674_at_e10g2000prf.googlegroups.com>


On 28 feb, 18:08, "Yagotta B. Kidding" <y..._at_mymail.com> wrote:
> Jan Hidders <hidd..._at_gmail.com> wrote in news:2c892007-19bb-45ce-b73c-
> 6cdc6c8de..._at_o77g2000hsf.googlegroups.com:
>
> > On 24 feb, 19:48, Marshall <marshall.spi..._at_gmail.com> wrote:
> >> Consider the algorithm to perform a natural join on two
> >> relation values. Just values: not tables in a database
> >> with a known schema or whatever. Just two plain relation
> >> values. The natural join specification *requires* the header;
> >> it is defined (in part) in terms of the header. So the header
> >> must be part of the value.
>
> > That is not correct. The natural join can be defined without referring
> > to the header.
>
> Quite right.  The header can always be extracted from a tuple by a simple
> function application:
>
> tuple = {(x, 1), (y, 2)}; first_el(tuple) => {x, y}

That's not simple function application.

  • Jan Hidders
Received on Thu Feb 28 2008 - 22:06:28 CET

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