Re: The Practical Benefits of the Relational Model

From: Mikito Harakiri <mikharakiri_at_yahoo.com>
Date: 3 Oct 2002 11:23:37 -0700
Message-ID: <bdf69bdf.0210031023.375229d8_at_posting.google.com>


Lauri Pietarinen <lauri.pietarinen_at_atbusiness.com> wrote in message news:<3D9BE382.A470F58C_at_atbusiness.com>...
> David Cressey wrote:
>
> > Don't expect people to stop saying that "A real relational system has never
> > been implemented". You will just be disappointed.
>
> Strangely enough, a "real" relational system _has_ been implemented - and that
> was a long time ago. See
>
> http://www.mcjones.org/System_R/bs12.html
>
> Obviously SQL does not even _try_ to be relational, and never has
> tried to. I am referring here to the fact that result tables can have
> duplicate rows.
> By the way, the SQL1999-standard does not even mention the word
> "relational".

What relational purity really buys us? Unability to express aggregation? Ignoring nulls? Not admiting nested subqueries? Total ignorance about domain operators? God forbid nesting/unnesting!? Recursion impotence?

It is often emphasized how beatuful relational theory is, because it is based on the set theory. While there is undoubtedly some connections, but may I ask why set union is a basic relational operator, and intersection is not? (Intersection could be expressed via combination of join and projection). Received on Thu Oct 03 2002 - 20:23:37 CEST

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