Re: Question about Date & Darwen <OR> operator
From: VC <boston103_at_hotmail.com>
Date: Fri, 2 Sep 2005 20:25:24 -0400
Message-ID: <4dGdnZ2dnZ1qQmiynZ2dnfFwhd6dnZ2dRVn-0J2dnZ0_at_comcast.com>
>> Marshall Spight wrote:
>>
>>>Mikito Harakiri wrote:
>>>
>>>>Assuming domains x in {1,2} and y in {a,b} what is the result of
>>>>
>>>>{(x=1)} <OR> {(y=a)}
>>>
>>>As I understand it, the result would be:
>>>
>>>x y
>>>---
>>>1 a
>>>1 b
>>>2 a
>>>
>>>
>>>which is
>>>{ (x, y) | x = 1 or y = a }
>>
>>
>>>From http://c2.com/cgi/wiki?RelationalAlgebra
>>
>> a OR b : An extended form of union; if the headings of the operands
>> differ, then "missing" attributes take on all possible values. Thus the
>> result may be very large or even infinite. When the operands have the
>> same heading, then this is the same as a traditional SQL UNION, except
>> that all duplicates are always removed.
>>
>> This informal description matches the other alternative. What is the
>> formal definition?
>>
Date: Fri, 2 Sep 2005 20:25:24 -0400
Message-ID: <4dGdnZ2dnZ1qQmiynZ2dnfFwhd6dnZ2dRVn-0J2dnZ0_at_comcast.com>
Hi,
"paul c" <toledobythesea_at_oohay.ac> wrote in message news:Tk5Se.66722$Hk.18346_at_pd7tw1no...
> Mikito Harakiri wrote:
>> Marshall Spight wrote:
>>
>>>Mikito Harakiri wrote:
>>>
>>>>Assuming domains x in {1,2} and y in {a,b} what is the result of
>>>>
>>>>{(x=1)} <OR> {(y=a)}
>>>
>>>As I understand it, the result would be:
>>>
>>>x y
>>>---
>>>1 a
>>>1 b
>>>2 a
>>>
>>>
>>>which is
>>>{ (x, y) | x = 1 or y = a }
>>
>>
>>>From http://c2.com/cgi/wiki?RelationalAlgebra
>>
>> a OR b : An extended form of union; if the headings of the operands
>> differ, then "missing" attributes take on all possible values. Thus the
>> result may be very large or even infinite. When the operands have the
>> same heading, then this is the same as a traditional SQL UNION, except
>> that all duplicates are always removed.
>>
>> This informal description matches the other alternative. What is the
>> formal definition?
>>
> > i assume you're referring to TTM page 56, which i misinterpreted for a > long time. >
I do not have TTM handy. Could you kindly reproduce the <OR> definition for my benefit ?
Thanks. Received on Sat Sep 03 2005 - 02:25:24 CEST