Re: Natural keys vs Aritficial Keys
Date: Wed, 27 May 2009 18:09:59 +0100
In message <qQdTl.27412$c45.10562_at_nlpi065.nbdc.sbc.com>, Brian Selzer
>"David BL" <davidbl_at_iinet.net.au> wrote in message
>> On May 23, 4:23 am, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
>>> Nope, that's still the first blunder: mapping object instances to
>>> tuples. Derived tuples are still tuples.
>> Date pointed out the obvious blunder in associating a class (which is
>> a type) with a relvar (which is a variable). Bob is correct in the
>> sense that derived relvars are still relvars.
>It is less clear that it is a blunder when associating a class (which is a
>type) with a relation scheme, which is not a variable, but rather very much
>like a type (at least under the specialization by constraint paradigm). The
>set of constraints that defines the set of all possible relations indirectly
>defines the set of all possible tuples. Why, then, should it be wrong to
>map object instances to tuples?
There are similarities between the things that OO theory deals with and the things that relational theory deals with. In some cases there may be a 1:1 mapping between concepts. But unless we can develop a coherent theory that subsumes both of these theories I think it is foolishly optimistic to expect to describe either of them using the other's concepts. There are pragmatic reasons why we need to translate between individual instances of classes and tuples but I don't see any route to dealing with this in any generic way.
My pet theory is that OO theory is going to have to rid itself of the concept of "class" before the two systems can be reconciled. A "class" is simply the result of selecting a subset of every possible object. A tuple is a subset of every possible entity. This is about as close to common ground as I can find, and I'm not convinced that it adds much to the debate.
-- Bernard PeekReceived on Wed May 27 2009 - 19:09:59 CEST