Re: Interpretation of Relations
From: Joe Thurbon <usenet_at_thurbon.com>
Date: Sat, 20 Jan 2007 11:21:54 GMT
Message-ID: <2007012021214043658-usenet_at_thurboncom>
>> On 2007-01-19 21:22:02 +1000, paul c <toledobythesea_at_oohay.ac> said:
>>
>>
>>
>> ...
>>
>>
>>
>> ...
>>
>>
>>
>> ...
>>
>>
>> Sorry, you've lost me there.
>>
>>
>> Can you do this? I thought that 'attributes' were effectively names of
>> domains, so if there are no attributes, there are no domains from which
>> you can "assign". What would it look like?
Date: Sat, 20 Jan 2007 11:21:54 GMT
Message-ID: <2007012021214043658-usenet_at_thurboncom>
On 2007-01-20 20:49:52 +1000, Bob Badour <bbadour_at_pei.sympatico.ca> said:
> Joe Thurbon wrote:
>> On 2007-01-19 21:22:02 +1000, paul c <toledobythesea_at_oohay.ac> said:
>>
>>> Joe Thurbon wrote:
>>
>>
>> ...
>>
>>>> >>>> Relation R_People = <<D_People>: {{Joe}}> >>>> Relation R_Hair Colour = <<D_People X D_Hair>: {{Joe, Blond}}> >>>> >>>> (The bit in the <> is the relation header, the subsequent sets are the >>>> relation body).
>>
>>
>> ...
>>
>>>> >>>> >>>> R_Hair Colour: <<D_People X D_Hair>: {}> >>>> >>>> indicates that I don't know the colour of Joe's hair. It really means >>>> >>>> NOT Joes hair is Red >>>> NOT Joes hair is Blond >>>> >>>> Is this right? ...
>>
>>
>> ...
>>
>>> >>> I think this is something that often trips me up - we can obtain tuples >>> that have no attributes only by projecting away other attributes (which >>> I believe is the purpose of TABLE_DEE and DUM)
>>
>> Sorry, you've lost me there.
>>
>>> or by declaring a relation that has no attributes and then "assigning" >>> (basically, this means memorizing) a value that stands for true or >>> false to that relation.
>>
>> Can you do this? I thought that 'attributes' were effectively names of
>> domains, so if there are no attributes, there are no domains from which
>> you can "assign". What would it look like?
> > Using your notation: > > Relation DEE = <<>:{{}}> > Relation DUM = <<>:{}>
Many thanks,
Joe
Received on Sat Jan 20 2007 - 12:21:54 CET