Re: What is analysis?

From: TroyK <>
Date: Wed, 5 Dec 2007 09:24:47 -0800 (PST)
Message-ID: <>

On Dec 5, 8:25 am, "David Cressey" <> wrote:
> "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.

You may be interested to check out the "Dee" project here:

An in-memory Python relational implementation "Inspired by Date and Darwen's Databases, Types and the Relational Model (The Third Manifesto)..."

I've used a "relations as first class programming citizens" programming model to very good effect for iterative application development.

TroyK Received on Wed Dec 05 2007 - 18:24:47 CET

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