Re: MV and SQL
Date: 23 Jan 2006 13:08:23 -0800
Message-ID: <1138050503.749821.147410_at_g14g2000cwa.googlegroups.com>
David Cressey wrote:
> "JOG" <jog_at_cs.nott.ac.uk> wrote
>
> > Ok, I have a question, with a bit of a build up: RM is based on the
> > satisfaction of a given predicate.
>
> [snip]
>
> > 1) Incomplete Data at entry time.
> > 2) Incorrect Design.
> > 3) Static Design which no longer matches how the real world has
> > shifted.
>
> [snip]
>
> >
> > In my eyes the fact that these 3 things happen so frequently indicates
> > that a system based on the satisfaction of a fixed predicate has poor
> > application to the real world and that the RM's solid mathematical
> > basis might be yet improved upon through integration of these issues.
> > Data is almost always incomplete, a designer cannot be omniscient and
> > will always make errors, but most importantly situations change.
> > Continually. It is preferable that we have a database model that
> > accomodates these factors: they are not orthogonal to data modelling
> > processes in the real world.
> >
>
> Without addressing your question about Pick, let me just comment on the
> above excerpts from your build up.
>
> First, the big to-do about nulls basically arises from the use of a single
> table row to encode more than one predicate. If one of the predicates is
> present, and the other one is absent, you get nulls.
> In theory, you could avoid nulls altogether by implementing a fully
> normalized design. In practice, it's better to live with nulls.
Hi david,
> Second, when you mention Incomplete data, that raises the question,
> incomplete with respect to what? Incomplete with respect to the real world
> requirements, or incomplete with respect to a designers idealized model of
> what the requirements are.
> The available data is the available data, whether it's "incomplete" or not.
> You can't store the unavailable data, no matter how clever you are. If the
> structure you've chose is too rigid to accomodate the data you've got, then
> there's a mismatch there. Whether or how Pick avoids that mismatch is
> something I'll leave to others.
> As far as incorrect design and obsolescent static design goes, that's a much
> longer subject.
>
> Two facets of that subject are: early binding vs late binding of design
> decisions, which is where my interest is going now, and the evolution of
> the schema as set forth by mountain man.
>
> Basically, you can't know what you are doing without fairly thorough
> analysis, and the art of analysis is still quite primitive, compared to
> design and implementation. If you aren't sure of what you're doing, late
> binding nearly always gives you better payback than early binding.
Sounds interesting - are there any good reference sources for this topic?
All best, Jim. Received on Mon Jan 23 2006 - 22:08:23 CET