Hi Mark,
On 14 Jul 2008, at 10:22, Mark Birbeck wrote:
I would say that RDFa has made the situation an order of magnitude
_less_ complicated, since authors and developers now have an easier
way to publish metadata;
Well, RDFa has made life simpler for those publishers whose
requirements are met well by RDFa. It has made life more complicated
for client developers, since they have to support yet another RDF
syntax.
I think RDFa is an important piece of the SemWeb technology puzzle,
but your claim that it “makes the situation an order of magnitude less
complicated” is unfounded, IMO.
as Kinglsey said, increasing the number of
ways to publish metadata increases the number of possible clients that
might consume the data:
Kingsley was talking about a situation where the publisher offers
*all* different methods of publishing RDF. Sure this increases the
number of theoretically possible clients, but it also increases the
cost of publishing RDF.
I also forgot to mention obvous use of RDFa in the HTML doc
which broadens the range of rdf aware user agents tha
commence RDF discovery from HTML
Does it not
also complicate the picture of making provenance statements using
named
graphs, if the subject of the triple could be both an HTML document
and
an RDF graph?
Is it possible to distinguish a graph URI? I hadn't realised that. It
would certainly be a good idea to have an rdf:Graph type, but I
hadn't realised that there was one.
There is no rdf:Graph type, and Tom didn't say there is one. Tom used
the words “RDF document” and “RDF graph” synonymously, which is a bit
sloppy.
However, is not an rdf:Graph a type of information resource?
Depends on how you squint at it. Technically speaking, a graph, as a
mathematical entity, is a fixed, immutable thing. An information
resource, on the other hand, can (and often does) vary over time. That
is, tomorrow it might have a different representation than today.
One could say that, in the case where we look at the Web through RDF
goggles, the concrete representation that we get back at any time from
an information resource is an RDF graph. The information resource
itself is not an RDF graph, but rather a function that returns an RDF
graph.
Now, if we ignore time and pretend that we just deal with a static,
frozen-in-time snapshot of the Web, then it's probably okay to pretend
that information resources are RDF graphs (because the function is
constant). This is what the RDF browsers out there do in practice,
they treat the Web as a set of named graphs, where the URIs of RDF
documents are the graph names.
An
RDF/XML document delivered from a web server is both a document and a
graph,
Yes and no, see above. It's true if you ignore time, but
architecturally speaking, Web documents (information resources) change
over time, while graphs are immutable.
but we have chosen to ignore that in the RDF architecture; it's
not possible to say 'this graph was published by', in RDF/XML, i.e.,
to talk about the information resource itself, because you will always
be talking about whatever the RDF/XML itself is about.
Huh? Of course it is possible to talk about information resources in
RDF. Assume that this is the content of an RDF document published at http://example.com/my_rdf_document.rdf
:
<rdf:Description rdf:about="http://example.com/my_rdf_document.rdf";>
<dc:publisher>Richard</dc:publisher>
<dc:date>2008-07-14</dc:date>
...
</rdf:Description>
This is an RDF document talking about itself. This is standard
practice, you can find examples like this in the RDF spec, and
everywhere in the wild.
(Note that in the example, I could have used rdf:about="", because an
empty URI is expanded to the URI of the document.)
But there is no reason that we could not enable this, and if we wanted
to go this route, RDFa+HTML allows it.
It's equally possible in RDFa and RDF/XML, today.
Best,
Richard
Regards,
Mark
--
Mark Birbeck, webBackplane
[EMAIL PROTECTED]
http://webBackplane.com/mark-birbeck
webBackplane is a trading name of Backplane Ltd. (company number
05972288, registered office: 2nd Floor, 69/85 Tabernacle Street,
London, EC2A 4RR)
