Re: Idempotence and "Replication Insensitivity" are equivalent ?

From: paul c <>
Date: Mon, 25 Sep 2006 13:05:40 GMT
Message-ID: <EuQRg.26775$1T2.10043_at_pd7urf2no>

Bob Badour wrote:

> paul c wrote:

>> David Cressey wrote:

>> But I'm also thinking that when you say 'project a relation onto its
>> attributes', if such a thing were permitted by some RM impl'n, what
>> *could* actually happen is that a relation with a single
>> relation-valued attribute would be formed and I suppose that
>> attribute's 'type' would be the name of the relation. But join is
>> usually the operator we expect to be able to undo a projection, so if
>> an impl'n did this, then I suppose it might want to undo the
>> rva-creating projection, and that might entail that it also have a way
>> of equating a relation with several attributes against a
>> single-attribute rva equivalent.
> Such as the relational equality operation?

Yes, but I suspect when I come up with examples, some trouble/ambibuity will show up.

>> In this admittedly oddball view of things, I wonder if the name of an
>> rva really matters? That's as far as I've got.
> What's oddball about it?

I wasn't clear - I didn't mean the rva can have any (unique) name we choose, just wondering if there are times when an rva could be unnamed without risk - that's what I meant by oddball.

p Received on Mon Sep 25 2006 - 15:05:40 CEST

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