# Re: History question -- Tarski and Codd

Date: 24 Oct 2002 11:58:04 +0200

Message-ID: <3db7c42c$1_at_news.uia.ac.be>

In article <231020021148525703%johnfl_at_cs.uoregon.edu>,
John Fiskio-Lasseter <johnfl_at_cs.uoregon.edu> wrote:

>In article <3dae743a$1_at_news.uia.ac.be>, Jan.Hidders

*><hidders_at_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