Re: More on lists and sets

From: x <x_at_not-exists.org>
Date: Thu, 23 Mar 2006 14:10:13 +0200
Message-ID: <dvu377$5i5$1_at_emma.aioe.org>


"Brian Selzer" <brian_at_selzer-software.com> wrote in message news:RhtUf.62412$dW3.21729_at_newssvr21.news.prodigy.com...
> "x" <x_at_not-exists.org> wrote in message news:dvp23n$rk4$1_at_emma.aioe.org...
> >
> > "Brian Selzer" <brian_at_selzer-software.com> wrote in message
> > news:2ISTf.3660$tN3.3129_at_newssvr27.news.prodigy.net...
> >
> >> A list of widgits cannot be converted to a set of widgits without
losing
> >> information.

> I said that the list can be represented as a path through a directed
graph.
> That implies both edges and verticies.

Sorry. My mistake.
A list of values can be converted to (represented as) a set of values.

> >> The value of the elements in a list or bag are augmented by their
> >> presence
> >> within the list or bag, and in a list, the value is augmented further
by
> > the
> >> position of the element. This augmentation gives each element
identity.
> >> "It's the third element in the list." "It's one of the five apples in
> > the
> >> bag." That identity is lost when converting a list to a bag or a set
or
> >> when converting a bag to a set.
> >
> > The the elements in a relations are augmented by their presence
> > within the relation, and in a relation, the value is augmented further
by
> > the
> > position of the element. This augmentation gives each element identity.
> > "It's the element of the domain 'bla' next to the element 'bla bla' in
the
> > domain 'bla bla bla'."
> > That identity is lost when converting a relation to a list.

> I disagree, at least as far as the Relational Model goes: the position of
a
> value in a relation is undefined and unimportant. A relation is a uniform
> set of r-tuples. An r-tuple is a set of named values. Therefore, the
> relation {{x = 5, y = 6}, {x = 3, y = 8}} is equivalent to the relation
{{y
> = 8, x = 3}, {x = 5, y = 6}}.

> On the other hand, the juxtaposition of a value with all other values in a
> given r-tuple does augment its value, as does its membership in the set of
> all other values in the relation with the same attribute name.

> I can't see how injecting order would cause a loss of identity or
> information. If anything, information would be gained as a result.

See the incident of the dog in the night. Received on Thu Mar 23 2006 - 13:10:13 CET

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