Re: The Theoretical Foundations of the Relational Model

JRStern wrote:
> And that's the big, black hole in relational theory: identity. OOP
> posits identity as important.

So does relational theory. It just requires that you define the attributes by which a tuple will be distinguished from all similar tuples. It further requires that these attributes are not synthetic, because a synthetic identifier doesn't unveil the true distinction.

The question devolves into a spitting contest about the time that OO and relational devotees attempt to define their arts as an attempt to structure reality. It's nothing of the sort of course; it's merely an attempt to structure understanding. As such, alternate and variant structures are valid, though each will present its important values in different areas.

I brought up the Laws of Form because GSB begins with the concept of distinction (as opposed to identity), and rebuilds the whole of Boolean logic around a single operator, in a system requiring only two axioms, not the five(?) of first-order logic. I'm not a mathematician, but his algebra of distinction is remarkably simple and enlightening.

Memories of when my children were young are illustrative here. At 2 years, one referred to all four-legged domestic quadrupeds as "cat", even the canines. He hadn't learnt to distinguish them. Later there were cats and dogs, but no Burmese or Dalmatians. The awareness of the distinction came before the words of course, and that's informative too. The structure of knowledge isn't based in facts, but in distinctions.

To my mind, the OO practitioner's insistence on disembodied identity is an attempt to record that some things are believed to be distinct, even though we might not yet be able to codify the distinction. In any case there will be a need to distinguish things, but we can delay defining the distinction. In other words, we can delay codifying our understanding.

In many cases involving abstract entities, this delay introduces a weakness. In particular, some abstract things appear to be subject at first sight to clear distinction, and hence leap up as candidate objects, whereas in fact when the distinction is sought, it turns out to be nowhere near so clear. In the meantime the whole design process may have been skewed.

I believe that it's these kinds of errors which are avoided by relational's demand that we codify true distinctions.

[Further musings on similarity between keys and relationships culled]

--
Clifford Heath