Re: Objects and Relations
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Thu, 15 Feb 2007 19:40:44 GMT
Message-ID: <0H2Bh.6878$R71.103099_at_ursa-nb00s0.nbnet.nb.ca>
>>On 15 fév, 18:05, "JOG" <j..._at_cs.nott.ac.uk> wrote:> Sigh. Let me take you back to what you initially wrote Cimode:
>>
>>
>>>Cimode wrote:
>>>
>>>>>>What I meant is that LegoBlock
>>>>>>and Location concepts should be separated if LegoBlock is to be
>>>>>>considered a relation. A relation *must* have a stable primary key.
>>>>>>Location is not a stable primary key therefore it does not identify
>>>>>>LegoBlock.
>>
>>>For a legoBlock, location is perfectly acceptable as an identifier. It
>>>is unstable, and so potentially a bad design choice, but still
>>>perfectly valid identifier at any instant. My complaint at what you
>>>wrote has nothing to do with hollow spheres (which require a location
>>>+radius identifier), and I will not get dragged off by a red herring.
>>
>>You have initially assumed that XYZ as a location. Now, you have
>>changed it to XYZR. My puposed was not to drag u into anything but to
>>point out an initial mistake you made in selecting XYZ only.
Date: Thu, 15 Feb 2007 19:40:44 GMT
Message-ID: <0H2Bh.6878$R71.103099_at_ursa-nb00s0.nbnet.nb.ca>
JOG wrote:
> On Feb 15, 7:05 pm, "Cimode" <cim..._at_hotmail.com> wrote: >
>>On 15 fév, 18:05, "JOG" <j..._at_cs.nott.ac.uk> wrote:> Sigh. Let me take you back to what you initially wrote Cimode:
>>
>>
>>>Cimode wrote:
>>>
>>>>>>What I meant is that LegoBlock
>>>>>>and Location concepts should be separated if LegoBlock is to be
>>>>>>considered a relation. A relation *must* have a stable primary key.
>>>>>>Location is not a stable primary key therefore it does not identify
>>>>>>LegoBlock.
>>
>>>For a legoBlock, location is perfectly acceptable as an identifier. It
>>>is unstable, and so potentially a bad design choice, but still
>>>perfectly valid identifier at any instant. My complaint at what you
>>>wrote has nothing to do with hollow spheres (which require a location
>>>+radius identifier), and I will not get dragged off by a red herring.
>>
>>You have initially assumed that XYZ as a location. Now, you have
>>changed it to XYZR. My puposed was not to drag u into anything but to
>>point out an initial mistake you made in selecting XYZ only.
> > No still not good enough I'm afraid. LegoPieces are not hollow > spheres, and do not have a radius. In their case picking XYZ as an > identifier is valid.
Technically, a lego piece occupies an interval, but since lego pieces are of fixed size, one can encode the interval as a location and an orientation. Received on Thu Feb 15 2007 - 20:40:44 CET