Re: What is analysis?

From: David Cressey <>
Date: Wed, 05 Dec 2007 15:25:29 GMT
Message-ID: <Jpz5j.6005$6k1.425_at_trndny02>

"Jon Heggland" <> wrote in message news:fj641f$m36$

> Bob Badour answered this; I'll just add a quote from Date's Introduction
> to Database Systems (2004):
> In his [1970] paper, Codd uses the term /time-varying relations/ in
> place of our preferred /relation variables/ (relvars). But /time-varying
> relations/ is not really a very good term. First, relations as such are
> /values/ and simply do not "vary with time" (there is no notion in
> mathematics of a relation having different values at different times).
> Second, if we say in some programming language, for example, DECLARE N
> INTEGER ; we do not call N a "time-varying integer", we call it an
> /integer variable/.
> (End quote)

Thanks for the above I'm going to try to incorporate "relvar" into my vocabulary, at the expense of misusing it several times in public. Be forgiving, while correcting me.

So far, I see at least one way in which the terminology can help my thinking.

There is no particular reason why a relvar has to be either persistent or stored in a database.
This allows one to discuss the logical features of data that is shared, whether or not that sharing is mediated by a database and a DBMS. It's always seemed to me that much of "database theory" has really been about "the theory of data sharing" rather than about storage, retrieval, and persistence as such. Many of the more interesting discussions in this newsgroup would still be interesting even if the data were transferred from one partner to another over some kind of "message bus" and never stored in a database at all!

So adding "relvars" to my vocabulary will allow me to think, at least primitively, about logical relational models at the application level and not just at the database level. It seems to me that this is where the battle between relational enthusiasts and object enthusiasts is really being waged, anyway. Received on Wed Dec 05 2007 - 16:25:29 CET

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