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Re: defining RDF graph syntax

From: Dan Connolly <connolly@w3.org>
Date: 28 Oct 2002 18:05:26 -0600
To: Pat Hayes <phayes@ai.uwf.edu>
Cc: w3c-rdfcore-wg@w3.org
Message-Id: <1035849927.25017.5638.camel@dirk>

On Mon, 2002-10-28 at 17:32, pat hayes wrote:
> Guys, I know I said I would alter the MT to conform to the other 
> docs, but after reading the other docs and the incoming comments, I 
> really think that it might be worth standardizing on the simpler view 
> of the RDF graph syntax that we already had worked out. Let me 
> suggest that we all say some verbal variation on the following.

yes, please.

> 1. An RDF graph is a set of triples. That is the basic definition.
> 2. a triple consists of three parts A B C where B is a uriref, A is a 
> uriref or a blank node, and C is a literal-thingie, uriref or blank 
> node.
> 3. We call them 'graphs' because they have a natural graphical (ie 
> pictorial) rendering as a collection of nodes and arrows with labels 
> written on them. But we are careful not to say that they ARE graphs 
> in any mathematical sense, because they aren't.
> 4.. As far as the syntax is concerned, blank nodes are just anonymous 
> syntactic 'things'. They are rather like existentially quantified 
> variables in logic, but one can also just think of them as blobs that 
> are used to connect the graph together.
> 5. Linear notations like Ntriples and XML use bnodeIDs to keep track 
> of the blobs, but those ID s shouldn't be thought of as names or 
> references, and they are local to a particular document.
> The basic point of this is that it does NOT distinguish between nodes 
> and their labels, and this is a real advantage, I suggest, in keeping 
> the exposition clear. It certainly avoids what is otherwise going to 
> be a minefield of getting the exact mathematical sense of 'graph' 
> correct, and since we don't need to go into this minefield, I suggest 
> that we keep out of it. In an earlier draft of the MT doc I had an 
> appendix which really did use graph-theory notions to explain the 
> syntax, and it was unreadable.
> It is fine to be informal and talk about 'labels' in the primer (or 
> anywhere else) as long as one is careful to say somewhere that since 
> two nodes never have the same label, that we can (and do) *formally* 
> equate labelled nodes with their labels.
> Pat
> PS. I could try to draft rewordings/patches if other editors felt it 
> might be useful, but I don't want to tread onto sacred ground or 
> anything. I think it can all be done with a few sentences here and 
> there, unless anyone really *wants* to get persnickety about 
> distinguishing references to a node from references to the label of 
> that node.
> -- 
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Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Monday, 28 October 2002 19:05:11 UTC

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