Re: Modeling question...
Date: Tue, 18 Nov 2008 09:02:43 -0800 (PST)
Message-ID: <7ea7b2bf-3814-4e2a-9d7d-1f162afad4b0_at_b31g2000prb.googlegroups.com>
On Nov 18, 10:39 pm, "Brian Selzer" <br..._at_selzer-software.com> wrote:
> "David BL" <davi..._at_iinet.net.au> wrote in message
>
> > Anyway, I think there are data entry applications where the concept of
> > "shared values" needs to be under user control. For example in the
> > data entry of a CAD drawing of a car the user may or may not want all
> > the wheels to share the same geometry. The problem with simple copy
> > and paste (and no logical sharing) is that any future edits to the
> > wheel geometry need to be repeated on every copy. The obvious
> > solution seems to be to reference a single shared geometry for a wheel
> > - hence the need for an abstract identifier. Are you suggesting that
> > an alternative is to instead use an integrity constraint! If so how
> > can you specify which geometries are logically tied and which are not
> > (ie even though they just happen to be equivalent in value at that
> > moment in time)? Doesn't that require abstract identifiers of some
> > sort anyway? I can't imagine that values that happen to be the same
> > are always assumed to be shared, because then it would be impossible
> > for a user to copy and paste a value in order to create a copy that
> > will subsequently diverge.
>
> I think that once a copy is made, the copy should be completely separate
> from the original.
> If there are shared components, such as the wheel
> geometry in your example, then those components should be segregated into a
> separate relation or set of relations.
> If two individuals have exactly the
> same attributes, then not enough attributes have been specified so that the
> individuals represented by values for those attributes can be distinguished.
> What you seem to be suggesting here has been suggested over and over: using
> an artifical identifier to represent the haecceity of an individual, or
> those attributes that are not relevant to the problem at hand but whose
> values would serve to distinguish two otherwise identical individuals, which
> is essentially (pun intended) the same thing.
The physicist Max Tegmark uses the term "baggage" to refer to the informal bindings between things in the real world and the identifiers (like "electron") that appear in all our existing models or descriptions of reality. He was using this term with reference to the question of whether it's possible for there to be a theory of everything described in a way that's completely free from baggage. He claimed the only way is to use sets of abstract identifiers that have "no baggage" because their meaning is only derived from their axiomatically defined relationships to each other. This is hand wavy stuff, but I think the distinction is relevant to DB theory. Received on Tue Nov 18 2008 - 18:02:43 CET