Re: Thinking about MINUS

Marshall wrote:
> On Jan 7, 8:48 am, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
>

>>paul c wrote:
>>
>>
>>>One of a couple of reasons this topic intrigues me is that certain
>>>scenarios aren't closed for operations in Codd's framework, eg., the
>>>case when two operands share an attribute name that has different types.
>>> I realize that a whole sub-industry has been built to deal with
>>>problems like this (based on various design disciplines, knowingly or
>>>unknowingly, I don't know), so many people would say I'm silly to
>>>wonder, but I can't help it.
>>
>>Wouldn't one end up with a resulting attribute defined as a union-type
>>in a relation with no rows?

I don't believe that there is any such thing as a type error and say that they are sort-of outside what we are talking about. There are user errors, programmer errors and designer errors and maybe some others, but no such thing, in our possible understanding, as something like a universal error. I think types stand on their own, unchangeable and constant and that it is in fact illogical and a fallacy to say that an agree-upon type is invalid, unless the details of its definition are somehow contradictory, that is, contradictory in a way that matters to the point.

When we define the qualities of a result, say its attributes, I think we are dismissing, out-of-hand and rightly, certain values and operational conditions. I think this is just as logical, maybe more logical if that makes any loose sense, than basing "valid procession" on the inputs.

Marshall, one reason I like your posts is because you are good at coming up with examples. Grateful if you'd try to counter the above with some.   Maybe my attitude is a useless one!

p Received on Mon Jan 08 2007 - 01:57:35 CET