Re: Lucid statement of the MV vs RM position?
From: paul c <toledobythesea_at_oohay.ac>
Date: Fri, 05 May 2006 15:24:38 GMT
Message-ID: <W6K6g.126571$P01.21187_at_pd7tw3no>
>
>
> No, R JOIN TABLE_DEE equals R. GROUP always adds an RVA; that's its
> purpose. I checked the GROUP/UNGROUP treatment in "Temporal Data and the
> Relational Model", and there they say explicitly that grouping on no
> attributes is equivalent to extending with TABLE_DEE.
>
> Since GROUP is a unary operator, I don't think it makes sense to talk
> about identity with respect to it (like TABLE_DEE is identity with
> respect to JOIN or whatever the terminology is).
> ...
Date: Fri, 05 May 2006 15:24:38 GMT
Message-ID: <W6K6g.126571$P01.21187_at_pd7tw3no>
Jon Heggland wrote:
> paul c wrote:
>
>>Jon Heggland wrote: >> >>>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. >>>... >> >>Oh, maybe this is a question for the authors. I thought it was >>equivalent to R JOIN TABLE_DEE
>
>
> No, R JOIN TABLE_DEE equals R. GROUP always adds an RVA; that's its
> purpose. I checked the GROUP/UNGROUP treatment in "Temporal Data and the
> Relational Model", and there they say explicitly that grouping on no
> attributes is equivalent to extending with TABLE_DEE.
>
> Since GROUP is a unary operator, I don't think it makes sense to talk
> about identity with respect to it (like TABLE_DEE is identity with
> respect to JOIN or whatever the terminology is).
> ...
Don't know why I guessed otherwise.
p Received on Fri May 05 2006 - 17:24:38 CEST