Re: Lucid statement of the MV vs RM position?

From: Jon Heggland <jon.heggland_at_idi.ntnu.no>
Date: Fri, 05 May 2006 08:25:04 +0200
Message-ID: <e3er3u$fad$1@orkan.itea.ntnu.no>

paul c wrote:
> Jon Heggland wrote:

>> Uh... If you group all the attributes in a relation, you get a relation
>> with a single attribute (the type of which is the same as of the
>> original relation) and a single tuple (containing the original
>> relation)? ...

>
> That's what I guessed. Also guess that when you group on none of them,
> the empty set is the identity attribute set for group.

I can't parse the above, but as I read the GROUP definition, R GROUP () AS RVA is equivalent to EXTEND R ADD TABLE_DEE AS RVA.

>>> I know that to put it loosely, ttm
>>> says they are the same when they have the same value,
>>
>> When they ARE the same value.
>> ...

>
> Maybe talking at cross-purposes, eg. what's in the system versus what's
> in our intentions.

I thought you were talking about determining whether two relation values were equal / the same.

>> I don't understand this---please use more standard notation if you want
>> to denote relations---but I think you are wrong. The integer denoted by
>> the expression "6/2" is the same as the one denoted by "3". ...

>
> But the relation denoted by one isn't the same as the other?

"3" does not denote a relation value. RELATION { TUPLE { 3 I } } does, and replacing "3" by "6/2" does not change which relation value it denotes.

-- 
Jon

Received on Fri May 05 2006 - 01:25:04 CDT