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Re: More on lists and sets

From: Marshall Spight <marshall.spight_at_gmail.com>
Date: 26 Mar 2006 19:00:38 -0800
Message-ID: <1143428438.178288.21430@t31g2000cwb.googlegroups.com>


David Cressey wrote:
> > >
> > > I'm confused. How does dataphor represent and manipulate tree
> structured
> > > data?
> >
> > With relations. I'm not sure I understand the question. Of course, the
> > relations are presented graphically using an table widget where the
> > tuples must necessarily be presented in some order---so you could say
> > there is a list involved at that level..?
>
> Here's what I mean:
>
> In SQL, tree structured data can be represented by adjacency lists, or by
> nested sets. Both of these, to some extent, can be seen as a "kludge" by
> those who are accustomed to dealing with tree structured data as it is
> represented in lisp, or in the Pick class of products as presented by Pick
> enthusiasts in here.

I think to have this conversation effectively, you have to distinguish the
kinds of trees you're talking about. I distinguish between what I call statically structured trees and dynamically structured trees. The static tree is like customer-invoice-lineitem: the structure is always known and is fixed. SQL has no trouble with such. It is the dynamically structured tree, like a parse tree or an org chart (with the attendant ancestor, etc. queries) that SQL has trouble with.

Marshall Received on Sun Mar 26 2006 - 21:00:38 CST

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