Re: Thinking about MINUS

From: paul c <toledobythesea_at_oohay.ac>
Date: Mon, 08 Jan 2007 00:57:35 GMT
Message-ID: <3Ggoh.562697$5R2.411367@pd7urf3no>

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?

>
>
> That's certainly one way to handle it. However I would be more inclined
> to think of it as a type error. Considering the relational operations
> as
> logic operations, if we use a variable to mean one thing (or kind of
> thing)
> in one equation, and another thing in another equation, we can't
> validly
> proceed using both at once.
>
>
> Marshall
>

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 Sun Jan 07 2007 - 18:57:35 CST