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Re: Idempotence and "Replication Insensitivity" are equivalent ?

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Mon, 25 Sep 2006 13:36:13 GMT
Message-ID: <hXQRg.38682$9u.331691@ursa-nb00s0.nbnet.nb.ca>


paul c wrote:
> 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.

If an attribute has no name, how are we to refer to it? Received on Mon Sep 25 2006 - 08:36:13 CDT

Original text of this message

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