Re: By The Dawn's Normal Light

From: Laconic2 <laconic2_at_comcast.net>
Date: Sun, 24 Oct 2004 15:19:12 -0400
Message-ID: <ZaednS2JA5mhneHcRVn-rg_at_comcast.com>


"Paul" <paul_at_test.com> wrote in message news:417bc639$0$43599$ed2e19e4_at_ptn-nntp-reader04.plus.net...
> Kenneth Downs wrote:
> > If the list is uniquely ordered I think you can do everything 1st order.
> > The inserted item must be either head, tail, or have defined before and
> > after nodes. You should also be able "SELECT..WHERE sequence>x" to get
all
> > items after item x. Don't know if you can guarantee unique sequence #'s
on
> > inserts without an occasional resequencing, like an index reorg. This
> > seems to be the absolute positioning case.
>
> But then if you wanted to insert a new entry at the beginning you'd have
> to shuffle all the higher entries' sequences up, which would be a
> second-order operation.
>

As far as "order in the list" goes, I'd like to go back to the "information principle" of the RDM, here. The informational priciple would say that, if order really matters, we'll encode it in the data. So if the order in a set of entries truly matters, we'll add a column called "sequence_number", or something like that, unless we can use one of the existing items of data to express the ordering.

Kindly note that in the Celko Nested Sets model of a hierarchy, the column called "lft" is really a sequence number. It's the sequence in the traversal of the tree. Or maybe it's the union of "lft" and "rgt". But hopefully you get the point either way.

So it's easy to express lists if you have sets or tables to work with. It's also easy to express sets, if you heve lists to work with, as long as you have a way to prevent your lists from becoming baggy. Received on Sun Oct 24 2004 - 21:19:12 CEST

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