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From: hidders@hcoss.uia.ac.be (Jan.Hidders)
Newsgroups: comp.databases.theory
Subject: Re: History question -- Tarski and Codd
Date: 24 Oct 2002 11:58:04 +0200
Organization: University of Antwerp
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In article <231020021148525703%johnfl@cs.uoregon.edu>,
John Fiskio-Lasseter  <johnfl@cs.uoregon.edu> wrote:
>In article <3dae743a$1@news.uia.ac.be>, Jan.Hidders
><hidders@hcoss.uia.ac.be> wrote:
>>
>> I've been wondering about that myself. There is for example an
>> interesting article by Jan Van den Bussche on the influence of Tarski's
>> work on database theory:
>> 
>>   http://citeseer.nj.nec.com/443292.html
>
>This was extremely helpful, although there are parts of it that for I'm
>stuck in stupidity.  "Cylindrification along a dimension i", for
>example, makes no sense to me, nor is the equivalence between the RA
>presented by Van den Bussche and that actually given by Tarski in the
>JSL paper completely obvious (that one I can probably work out myself,
>though).

Yes, cylindrifaction is a bit mysterious because it seems such a destructive
operator. Basically what it does is fill up one column with all the values
in your domain. So if you have a relation:

  { ( a, b, c ),
    ( b, c, a ) }

and you cylindrify it on column 2 then you get

  { ( a, a, c ),
    ( a, b, c ),
    ( a, c, c ),
    ( b, a, a ),
    ( b, b, a ),
    ( b, c, a ) }

I don't exactly remember the simulation of the relational algebra. The union
is given. The intersection is given by A INTERSECT B = COMPL ( COMPL(A)
UNION COMPL(B) ). The difference is then given by A MINUS B = A INTERSECT
COMPL(B). The selection is simulated by intersecting with the corresponding
diagonal relation. The projection and cartesion product have slipped my mind
at the moment.

>On a side note, JAN HIDDERS:  I've tried to send an email "thank you"
>for the additional message you sent, relaying Van den Bussche's
>thoughts (and the translation from Flemish for this monolingually
>challenged American :-)  It's bounced twice, though.  Anyway, thanks!

Yes, thanks, and sorry for not configuring my trn properly. :-) I hope
that's better now.

-- Jan Hidders