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Named RDF Graphs - A Warning

From: Sean B. Palmer <sean@miscoranda.com>
Date: Tue, 18 Dec 2007 12:43:09 +0000
Message-ID: <b6bb4d890712180443o35de84p8f0e68e33034ff48@mail.gmail.com>
To: semantic-web@w3.org

Jeremy has proposed @rdf:graph. I like the idea of letting RDF/XML
talk about graphs, but I worry that we will end up with confusions
that we had with XML namespaces only worse.

When SPARQL talks about URIs for naming graphs, it doesn't mean that
that URI identifies the graph. So for example, if you have a graph
named "http://example.org/powder" that *doesn't* mean that you can
say:

<http://example.org/powder> a RDFGraph .

This is just like XML namespaces. When you have
xmlns="http://www.w3.org/1999/xhtml", is the following true?

<http://www.w3.org/1999/xhtml> a Namespace .

No, it is not. The URI is just being used as a unique name. But it's
very difficult for people to make a new space of URI usage in their
heads without getting confused, so we end up with this:

"Another benefit of using URIs to build XML namespaces is that the
namespace URI can be used to identify an information resource that
contains useful information, machine-usable and/or human-usable, about
terms in the namespace. This type of information resource is called a
namespace document."
- http://www.w3.org/TR/webarch/#namespace-document

This isn't so bad with namespaces, but I think it will be for graphs.
People will start using using HTTP URIs that return a 200 to identify
RDF Graphs, whereas RDF Graphs are disjoint with information
resources. Think about what else you can get from an RDF/XML document:
an XML infoset, a sequence of unicode characters. The graph is not the
document; it's not the information resource.

It would be nice to have a URI that identifies a graph, rather than
just sparql:names it, because it would be less confusing having yet
another new space for URI usage. I'll bet many people hadn't even
noticed the difference, and probably still won't understand it after
reading this message.

Think about it, though. You don't want the TAG kicking down your door at 3am.

-- 
Sean B. Palmer, http://inamidst.com/sbp/
Received on Tuesday, 18 December 2007 12:43:18 GMT

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