Re: RM formalism supporting partial information
Date: Tue, 20 Nov 2007 18:11:49 GMT
Alfredo Novoa wrote:
> On 16 nov, 18:44, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
>>> In a tuple I would call "tuple elements" to the pairs formed by name >>> and value. >> I am not sure the name is necessarily part of the element other than to >> identify it.
> But identification is essential.
>> I am not sure if that is clear enough. In mathematics, we >> sometimes use names and we sometimes use position to identify the >> elements of tuples.
> In "traditional" mathematics we use positions, in RM mathematics we
> use names to identify the elements of tuples. This is one of Codd's
> aportations. RM tuples and "traditional" tuples are not the same
> mathematical constructions.
D&D formal definitions mention triples (which I think are ordered) and a triple mentions an attribute's name:
"Let tr be a tuple that conforms to Hr; i.e., tr is a set of ordered triples of the form <A,T,v>, one such triple for each attribute in Hr."
To me, this doesn't seem to admit empty subsets of triples. I gather they get around this with their <remove> op instead of the more common projection operator. Received on Tue Nov 20 2007 - 19:11:49 CET