Re: Aggregation is Inverse of Join
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Tue, 16 Jan 2007 00:42:31 GMT
Message-ID: <XbVqh.1471$1x.22392_at_ursa-nb00s0.nbnet.nb.ca>
>> On Jan 15, 8:41 am, "Walt" <wami..._at_verizon.net> wrote:
>>
>>> "Marshall" <marshall.spi..._at_gmail.com> wrote in
>>>
>>>
>>>> Well, I've run out of steam. More later.
>>>
>>>
>>>> Marshall
>>>
>>>
>>>> PS. I told you I wasn't organized.
>>
>>
>>
>>> Interesting. It's going to take me weeks to get it.
>>>
>>> In the meantime, what is the inverse of Project?
>>
>>
>>
>> I think the usual term is "extend."
>>
>> In the relational lattice, project is just a specialization of the
>> inner union, with one of the operands having cardinality zero.
>>
>>
>> Marshall
>>
Date: Tue, 16 Jan 2007 00:42:31 GMT
Message-ID: <XbVqh.1471$1x.22392_at_ursa-nb00s0.nbnet.nb.ca>
paul c wrote:
> Marshall wrote: >
>> On Jan 15, 8:41 am, "Walt" <wami..._at_verizon.net> wrote:
>>
>>> "Marshall" <marshall.spi..._at_gmail.com> wrote in
>>>
>>>
>>>> Well, I've run out of steam. More later.
>>>
>>>
>>>> Marshall
>>>
>>>
>>>> PS. I told you I wasn't organized.
>>
>>
>>
>>> Interesting. It's going to take me weeks to get it.
>>>
>>> In the meantime, what is the inverse of Project?
>>
>>
>>
>> I think the usual term is "extend."
>>
>> In the relational lattice, project is just a specialization of the
>> inner union, with one of the operands having cardinality zero.
>>
>>
>> Marshall
>>
> > Surely, it's join. > > p
I strongly doubt project has an inverse as it is a lossy transformation. Received on Tue Jan 16 2007 - 01:42:31 CET