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Re: nodes and node labels [was New document: revised version for WG review]

From: Graham Klyne <Graham.Klyne@MIMEsweeper.com>
Date: Tue, 30 Jul 2002 12:12:10 +0100
Message-Id: <5.1.0.14.2.20020730120319.03bdacc0@127.0.0.1>
To: Dan Connolly <connolly@w3.org>
Cc: Jeremy Carroll <jjc@hplb.hpl.hp.com>, w3c-rdfcore-wg@w3.org

Dan,

[Trying to clarify rather than take a position here]

Jeremy's comment was aimed at the notion of a graph itself being "tidy" (no 
label appears more than once), separately from the hotly debated issue of 
tidy literal interpretations.  This document does not take any position on 
the issue of tidiness of literal interpretations, though it does say that a 
graph is syntactically tidy with respect to literals and URIrefs.

I think the key statements are:

Section 3.3:
[[
A tidy set of nodes is one in which no two nodes have equal labels.
]]

and

Section 3.5:
[[
The set of nodes of an RDF graph is tidy (per definition in section Nodes).
]]

This document section merely defines the abstract graph syntax, and says 
nothing about its semantics.

#g
--

At 03:50 PM 7/29/02 -0500, Dan Connolly wrote:

>On Mon, 2002-07-29 at 15:45, Jeremy Carroll wrote:
> >
> >
> > I wanted to draw the WG attention, particularly Pat, to a mathematical 
> issue
> > with the graph syntax.
> >
> > I do not believe that this has any substantive content, but is merely
> > aesthetic!
> >
> >
> > In the very first version of the model theory, the RDF graph was described
> > as having nodes some of which had labels, and the labels were URI refs or
> > strings.
> >
> > In the most recent version, some of the nodes are URI refs and some of the
> > nodes are strings (and none of the nodes are labelled).
> >
> > In the new document draft, we have reverted to the earlier version using
> > explicit node labels.
> >
> > The motivations for this include:
> > - tidying a graph is an explicit operation rather than implicit by
> > mathematical construction
> > - it easier to modify the exact tidyness specification (if the WG changes
> > its mind about whether literals are tidy or not - uriref nodes don't 
> seem in
> > doubt).
> > - implementations will almost all use nodes with explicit labels.
> >
> >
> > The first point is the decisive one. From a mathematical point of view 
> Pat's
> > latest model theory treatment in which the URI refs and strings *are* the
> > nodes is extremely elegant. Tidiness just falls out and no text needs to be
> > spent on it.
>
>Indeed.
>
>(deep sigh of relief)
>
> > However, in practice any implementor needs to be aware of tidiness as an
> > operation which has to be coded,
>
>???
>
> > and any user needs some understanding of
> > tidiness.
>
>??????
>
>I disagree.
>
>Care to elaborate?
>
> > Thus, I felt that Pat's earlier treatment, while a little more
> > clunky, is clearer for our intended audience: implementators, users, web
> > architects - rather than mathematicians.
>
>I disagree.
>
> > Although I raise this issue now, I would hope that any debate, if debate is
> > needed, can be postponed until after the first WD. I don't think this is a
> > crucial issue either way.
> >
> > Jeremy
> >
> >
>--
>Dan Connolly, W3C http://www.w3.org/People/Connolly/
>see you in Montreal in August at Extreme Markup 2002?

-------------------
Graham Klyne
<GK@NineByNine.org>
Received on Tuesday, 30 July 2002 07:30:33 EDT

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