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RDF Syntaxes 2.0

From: Dave Beckett <dave@dajobe.org>
Date: Sun, 24 Jan 2010 21:38:05 -0800
Message-ID: <4B5D2E3D.3000700@dajobe.org>
To: semantic-web@w3.org
I've been diligently ignoring the RDF 2.0 threads, especially on Syntax
since I've been there before [1].  Firstly I'd endorse what Jeremy Carroll
says at [2] about the features.

I think I'm qualified as an expert on RDF graph serializations / syntax
- I edited the revised RDF/XML (2004)
- I co-created N-Triples
- I created Turtle
- played with making an atom-triples [3]

and I implemented all of the above plus GRDDL, RDFa (via librdfa), Atom and
RSS*es, RDF/JSON, ... in Raptor http://librdf.org/raptor/

People moan about RDF/XML and have for years.  I even wrote down in great
detail the flaws in [1].  Over all that time nobody has come up with a
credible and complete XML syntax alternative that stuck, even myself.  Let
me summarize the ones I know:
- TriX: had little takeup
- RXR[1]: ditto
- GRIT: new, but flawed since it can only represent trees (no named bnodes)

The fundamental problem I think with using XML to write down graphs is:

  People looking at XML expect they are looking at a hierarchical Tree.

So writing a Graph in an XML Tree is just going to always fail the
simplicity test.  This might come from using the XML DOM or looking at HTML,
XHTML, but it's pretty embedded in the mind.

Right now I'd dismiss any XML format for any "simple" or "obvious" way to
write down RDF graphs that will be accepted by new users.

  (Aside: There's also a technical argument that no XML format can ever
   represent all RDF graphs since RDF allows Unicode codepoints that are
   not allowed in XML).

Now this isn't a problem just with XML, it's also true of other non-XML
formats that are serial hierarchical documents.  That means formats like
JSON, which cannot even out-of-the-box represent anything that is not a
tree, since it has no ID/REF mechanism.

Of course, apart having dealt with the RDF/XML I also invented Turtle
(based on the N3 syntax, simplified) and although it's a non-XML syntax,
does seem to be in the sweet spot for users understanding it, without
having the hierarchical document expectation.   Yes, Turtle is close to
JSON/python in syntax design space but this doesn't seem to have been
a problem.

So I'm happy with how Turtle turned out and that should be the focus of RDF
syntax formats *for users*.  It does need an update and I'll probably work
on that whether or not a new syntax is part of some future working group - I
have a pile of fixes to go in.  Adding named graphs (TRIG) might be the next
step for this if it was a standard.

It may be there is a need for a better machine format, but please don't mix
them.  Also, machines can read Turtle RDF :)

Consider this stream of conciousness RDF syntax thoughts as the basis of my
position paper for the RDF Next Steps workshop [4]

Also posted to my blog as


[1] Modernising Semantic Web Markup

[2] http://lists.w3.org/Archives/Public/semantic-web/2010Jan/0144.html

[3] Atom Triples Internet Draft from 2008

[4] RDF Next Steps
Received on Monday, 25 January 2010 05:38:34 UTC

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