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Re: Minutes of RDF-WG F2F, Day 2

From: Pierre-Antoine Champin <pierre-antoine.champin@liris.cnrs.fr>
Date: Wed, 31 Oct 2012 01:00:55 +0100
Message-ID: <CA+OuRR-v2SgV_2eLrNYWhdrz+Gum02AW1W1hc5fhHsT_o3_cjw@mail.gmail.com>
To: Dan Brickley <danbri@danbri.org>
Cc: RDF Working Group WG <public-rdf-wg@w3.org>
Hi Dan,

too bad indeed you could not come.

Regarding the rdf:Seq issue, I really don't have a strong opinion
anymore. However, I would like to point out that, IMHO, the whole XMP
argument is moot, for the following reasons (I first keep them short
to spare the readers -- I detail below) :

* XMP is not interoperable with RDF as standard RDF parser may parse
XMP incorrectly
* XMP is not interoperable with RDF as standard RDF serializers may
generate invalid XMP
* XMP is using rdf:Bag and rdf:Alt which I think we agreed to mark as archaic

so I dont think that the rdf:Seq issue makes a big difference in
alienating the XMP people... :-/

Granted, the interoperability problems are corner cases, and in 99% of
cases, standard RDF tools will probably interoperate very well with
XMP-dedicated tools. And granted, that's a nice thing that Adobe (at
least tried to) adopt RDF. But marking a feature as archaic is, in my
view, a minor issue (its *not* deprecation) compared to the issued
raised above.

  pa

PS: more detail for the interested readers

Refering to XMP Part 1 (Data model, Serialization and Core Properties)
http://wwwimages.adobe.com/www.adobe.com/content/dam/Adobe/en/devnet/xmp/pdfs/cs6/XMPSpecificationPart1.pdf


1/ XMP is not interoperable with RDF as standard RDF parser may parse
XMP incorrectly

XMP defines its own data model in section 6, and 6.2 states :

> All names in XMP shall be XML expanded names, consisting of a namespace URI
> and a local name.

Meaning that

  <prop xmlns="xmlns:xmp="http://example.org/ns1-">foo</prop>

is *not* equivalent to (e.g.)

  <ns1-prop xmlns="xmlns:xmp="http://example.org/">foo</n1-prop>

although standard RDF parsers will actually parse the same thing.
While this SHOULD not happen (XMP recommends to end namespace URIs
with "/" or "#", basically), this *could* happen in theory.
Note that, according to annex B.3:

> This is not a problem for an XMP processor that avoids use of the RDF triple representation.

So interoperability with RDF is clearly not seeked here.


2/ XMP is not interoperable with RDF as standard RDF serializers may
generate invalid XMP

XMP defines its syntax in terms of the RDF/XML syntax, *not* in term
of the RDF abstract syntax (as emphasized in annex B.3, see above).
More precisely and disturbingly, XMP only allows a *subset* of the
RDF/XML syntax, explicitly prohibiting some variants (see 7.9.3). For
example

  <rdf:Seq><rdf:li>foo</rdf:li><rdf:li>bar</rdf:li></rdf:Seq>

may not be serialized in XMP as

  <rdf:Seq><rdf:_1>foo</rdf:_1><rdf:_2>bar</rdf:_2></rdf:Seq>

nor as

  <rdf:Description>
    <rdf:type rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#Seq">
    <rdf:li>foo</rdf:li><rdf:li>bar</rdf:li>
  </rdf:Description>

However, I can imagine that some RDF serializer may provide one of
these outputs.



On Tue, Oct 30, 2012 at 6:24 PM, Dan Brickley <danbri@danbri.org> wrote:
>
> Hi Folks,
>
> On 30 October 2012 10:07, Richard Cyganiak <richard@cyganiak.de> wrote:
> > Today's minutes, slightly cleaned up:
> > http://www.w3.org/2011/rdf-wg/meeting/2012-10-30
>
> Thanks. Sorry I couldn't make it to TPAC - new job, bad timing, so the
> minutes are much appreciated.
>
> Just reading these, I'd like to speak up in favour of keeping rdf:Seq.
>
> rdf:List is equally annoying to use, and in some ways more fragile.
>
> rdf:List won't get used any more enthusiastically, by virtue of
> declaring its annoying rival rdf:Seq to be no-longer-supported.
>
> If the WG is trying to alienate the XMP folks and encourage them to
> re-visit their decision to use RDF, this seems a logical move.
> Otherwise it's the latest in a long line of the RDF community being
> its own worst enemy.
>
> "Millions (maybe billions) of files around the world using RDF?
> Awesome, let's declare the markup they use to be broken! That'll teach
> them to follow W3C recommendations..."
>
> Dan
>
> ps. I'm in transit between employers, but will be rejoining the WG as
> a Google employee in the near future. If there are substantive changes
> to RDFS I welcome Arnaud's offer of editing help (well, I welcome it
> anyway, thanks Arnaud!); if it's relatively small tweaks and a bit of
> polish, I have the time for that. There's a rough version in Mercurial
> already. We only have a couple of issues against RDFS in the tracker
> so far; are there more decisions that need reflecting?
>
Received on Wednesday, 31 October 2012 00:01:23 GMT

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