Re: Date and McGoveran comments on view updating 'problem'

From: <>
Date: Fri, 12 Dec 2008 10:31:09 -0800 (PST)
Message-ID: <>

On Dec 12, 3:34 am, JOG <> wrote:
> Ah, of course, the header. Now it makes sense - distributivity
> requires correspondence in header unions. It might be worth noting
> that I did not make the assumption that headers intersect when the two
> components of a join are disjunct (and on a quick reglance of your
> work could see no mention of this). In "First Steps in Relational
> Lattice" you very neatly define a natural join over two binary
> relations as:
> A(x,y) ^ B(y,z) = {(x,y,z) | (x,y)EA & (y,z)EB }
> However, this makes no mention of headers at all, leaving ambiguity
> that might be worth just rectifying in future papers (to avoid any
> confusion in those like me who don't assume a theoretical requirement
> for header constructs).

I never realized that this set definition might be a stumbling block! Jan was criticizing this section of the manuscript as well. My line of thought was: "OK, everybody knows what natural join is, we don't need set definition for that. Inner union, however, is a new construct, so it has to be defined (in set notation). In case if a reader has a problem with inner union definition why not to provide a natural join definition? Then the reader can consolidate definition for familiar operation with his notation confusion". It looks like this idea didn't work:-)

> Nevertheless all very interesting stuff Vadim! Have you formally
> published your work in this area?

Alas, just missed PODS deadline by couple of days! Received on Fri Dec 12 2008 - 19:31:09 CET

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