Re: Lucid statement of the MV vs RM position?

dawn wrote:
> JOG wrote:
> > dawn wrote:
> > > JOG wrote:
> > > > dawn wrote:
> > > > > Jan Hidders wrote:
> > > > > > dawn wrote:
> > > > > > > Jan Hidders wrote:
> > > > > > > > dawn wrote:
> [time for a snip]
> > So your remaining objections with the RM establishment (as I have read
> > them) seem to distill to whether a statement such as:
> >
> > "Barney is_colour green and is_colour purple"
> >
> > translates best to which of the following propositions:
> >
> > 1) colour(Barney, green) && colour(Barney, purple)
> > 2) colour(Barney, {green, purple} )
> >
> > Would you not say that with bit of logical manipulation we could
> > probably show that the first is preferable? J.

>

Well queries interact with the logical model, not humans or their notion of an entity directly. It's a layer down. I have read and understand your standpoint on this, but I really think there is a distinction to be made - I try and describe it below.

> and no interpretation of the meaning of the data ever

I don't think this follows: both mean the same thing - the original proposition.

> then 1) has the charm of mathematical simplicity (1st order
> logic) with no downside.

Consider that the propositions:

1. "Barney has green fur and purple fur", "Oscar has green fur and black fur"

are logically identical to:

2) "Barney and Oscar have green fur",
"Barney has purple fur",
"Oscar has black fur"

If we're agreed there then consider that the first - in MV style - would give something like:
colour( Barney, {green, purple} ) &&
colour( Oscar, {green, black})

But the second set of propositions in MV style gives us:

colour( green, {Barney, Oscar} ) &&
colour( purple, {Barney}) &&
colour( black, {Oscar})

The first "human interface" refers to entities "Barney" and "Oscar". The second, has an "interface" consisting of the entities "green"-ness, "purple"-ness and "black"-ness. Which is correct? Neither and both, because they are artifices. Who knows which will be appropriate to the user? An XML or MV style prejudges that decision, and with large shared data, who's future use is unpredictable, it seems essential to me to avoid that interface-prison.

With RDBMS, despite thei 3VL issues, there is no prejudice as to this choice - both sets of propositions, 1 and 2, encode down to the same things - just as they should being logically identical.

> I reserve the right to change my mind on that, however. Cheers! --dawn

I'd reckon that this is the most important quality anyone can have in life. That and a high tolerance for alcohol. Received on Tue May 02 2006 - 16:06:05 CEST