Re: atomic
From: paul c <toledobythesea_at_ooyah.ac>
Date: Wed, 07 Nov 2007 02:39:45 GMT
Message-ID: <Rz9Yi.187005$th2.16058_at_pd7urf3no>
>
> This isn't quite right. Instead the definition should be
>
> t1 <= t2 if both the following
>
> for each attrib a in (attribs(t1) intersect attribs(t2)),
> t1(a) is a subset of t2(a)
>
> for each attrib a in (attribs(t1) \ attribs(t2)),
> t1(a) = {}
>
> ...
Date: Wed, 07 Nov 2007 02:39:45 GMT
Message-ID: <Rz9Yi.187005$th2.16058_at_pd7urf3no>
David BL wrote:
> On Nov 6, 3:45 pm, David BL <davi..._at_iinet.net.au> wrote:
>> On another note, I've been thinking of an interesting partial ordering >> on mv-tuples that is associated with information redundancy : >> >> t1 <= t2 if >> attribs(t1) is a subset of attribs(t2) and >> for each attrib a in attribs(t1), t1(a) is a subset of t2(a) >> >> t1 <= t2 means that t1 is (information) redundant with respect to t2.
>
> This isn't quite right. Instead the definition should be
>
> t1 <= t2 if both the following
>
> for each attrib a in (attribs(t1) intersect attribs(t2)),
> t1(a) is a subset of t2(a)
>
> for each attrib a in (attribs(t1) \ attribs(t2)),
> t1(a) = {}
>
> ...
Sorry if I missed something but does "\" mean divide? (If so, which divide, Codd's or another one?) (not saying I understand the rest, because I'm a slowpoke, but I do think the first version can be expressed with D&D "semijoin".) Received on Wed Nov 07 2007 - 03:39:45 CET