Re: choice of character for relational division
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Sat, 31 Mar 2007 16:55:03 GMT
Message-ID: <HnwPh.17762$PV3.183907_at_ursa-nb00s0.nbnet.nb.ca>
>> Let us consider the choice of characters to use for
>> relational operators. It might be desirable to use
>> different characters for the relational operators from
>> the scalar ones, so we avoid using * for join, even
>> though it is in some sense a product operator.
>>
>> Set subtraction already has a standard character
>> in common usage: \
>>
>> But we also need a character for relational division.
>> The / character is often used, but that's the same
>> as numerical division. Bummer.
>>
>> So, if you had to choose an ascii character for
>> relational division, which one would you use
>> and why?
Date: Sat, 31 Mar 2007 16:55:03 GMT
Message-ID: <HnwPh.17762$PV3.183907_at_ursa-nb00s0.nbnet.nb.ca>
Bob Badour wrote:
> Marshall wrote: >
>> Let us consider the choice of characters to use for
>> relational operators. It might be desirable to use
>> different characters for the relational operators from
>> the scalar ones, so we avoid using * for join, even
>> though it is in some sense a product operator.
>>
>> Set subtraction already has a standard character
>> in common usage: \
>>
>> But we also need a character for relational division.
>> The / character is often used, but that's the same
>> as numerical division. Bummer.
>>
>> So, if you had to choose an ascii character for
>> relational division, which one would you use
>> and why?
> > > Does a unique relational "division" exist? If "product" has a completely > different name "join", why should a "divide" use the same name? > > If we have an equality operation for relations, does a "divide" > operation give us all that much?
Hmmmm... and division isn't really the inverse of join. It is the inverse of cross product which is a special case of join. Is the divide operation you contemplate the inverse of cross product or a more general operation which is the inverse of join? Received on Sat Mar 31 2007 - 18:55:03 CEST