Re: Authoritative References

From: Dawn M. Wolthuis <dwolt_at_tincat-group.comREMOVE>
Date: Sat, 2 Oct 2004 16:38:34 -0500
Message-ID: <cjn751$qi5$1_at_news.netins.net>


"Laconic2" <laconic2_at_comcast.net> wrote in message news:xpednTVS-LGDZcrcRVn-uQ_at_comcast.com...
>
> "Alfredo Novoa" <alfredo_at_ncs.es> wrote in message
> news:4157e15e.265937_at_news.wanadoo.es...
>
> > It is only a dictionary of algorithms and data structures, but they
> > don't have a definition of relation or tuple.
>
> Actually NIST does have a definition of "relation". Here it is:
>
> http://www.nist.gov/dads/HTML/relation.html
>
> It's valid in its own context, but not especially useful in the context of
> database theory.

Fortunately, Codd thought it useful as that is pretty much like the definition he started with for a relation -- it is the definition of a mathematical relation. I prefer to work with a subset of relations -- functions. These turn out to be very useful in computing since for each input there is exactly one ouput, rather than possibly more than one. That is, there is a unique key for each "row" in the relation, thereby making it a function with that key as the input and the row it maps to as the output. Most database designers make each relation a function anyway, so formalizing that only helps take some of the guess work out and permit us to work with data as functions as well as working with behavior as functions.

--dawn Received on Sat Oct 02 2004 - 23:38:34 CEST

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