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Re: ACTION: elaborate on 4.4

From: Eric Prud'hommeaux <eric@w3.org>
Date: Fri, 11 Jun 2004 13:21:50 +0900
To: Kendall Clark <kendall@monkeyfist.com>
Cc: public-rdf-dawg@w3.org
Message-ID: <20040611042150.GC12275@w3.org>

On Tue, Jun 08, 2004 at 05:06:20PM -0400, Kendall Clark wrote:
> 
> On Mon, Jun 07, 2004 at 01:17:39PM -0400, Kendall Clark wrote:
> 
> > Open design issues (many of which I expect can be analogized to
> > content negotiation in HTTP) include:
> >    
> >    - how to request one's preferred exchange serialization; 
> >    - whether it's a request or a negotiation;
> >    - whether to identify exchange serializations by Internet Media Type, by
> >      URI, or by canonical short name;
> 
> Just to be clear, the IMT option won't really work here. IMT aren't
> generally fine-grained enough to distinguish different XML
> vocabularies (which sucks, really). I think, then, short-name or URI
> are the real options.

There are three tiers in the xml subtrees as specified by RFC 3023.
It specifies (or maybe just references) a bunch of popular media types:
[[
   8.14 Application/xml-external-parsed-entity with UTF-16BE Charset  23
   8.15 Application/xml-dtd  . . . . . . . . . . . . . . . . . . . .  23
   8.16 Application/mathml+xml . . . . . . . . . . . . . . . . . . .  24
   8.17 Application/xslt+xml . . . . . . . . . . . . . . . . . . . .  24
   8.18 Application/rdf+xml  . . . . . . . . . . . . . . . . . . . .  24
   8.19 Image/svg+xml  . . . . . . . . . . . . . . . . . . . . . . .  24
]]

One feature of using media type selection is that it allows us to take
advantage of the notion that the semantic content should be consistent
from one serialization to another. Thus, you can get the URL for a
query and give the URL to different clients which prefer different
result formats.

For example: suppose the W3C mail search service provided results in
different languages; you could

GET 'http://www.w3.org/Search/Mail/Public/search?keywords=20040608210620.GC15635%40monkeyfist.com&hdr-1-name=subject&hdr-1-query=&index-grp=Public__FULL&index-type=t&type-index=public-rdf-dawg'

and get back a bunch of HTML, 

GET -H 'Accept: application/rdf+xml' 'http://www.w3.org/Search/Mail/Public/search?keywords=20040608210620.GC15635%40monkeyfist.com&hdr-1-name=subject&hdr-1-query=&index-grp=Public__FULL&index-type=t&type-index=public-rdf-dawg'

and get back some RDF:

<?xml version="1.0" encoding="iso-8859-1"?>
<rdf:RDF xmlns:email="http://www.w3.org/2000/10/swap/pim/email#"
    xmlns:log="http://www.w3.org/2000/10/swap/log#"
    xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
    xmlns:search="http://www.w3.org/Team/2001/09/search/search.pl#"
    xmlns:session="http://dev.w3.org/cvsweb/perl/modules/W3C/Util/W3CDebugCGI.pm">...</rdf:RDF>

GET -H 'Accept: text/x-n3' 'http://www.w3.org/Search/Mail/Public/search?keywords=20040608210620.GC15635%40monkeyfist.com&hdr-1-name=subject&hdr-1-query=&index-grp=Public__FULL&index-type=t&type-index=public-rdf-dawg'

and get back some n3:

@prefix email: <http://www.w3.org/2000/10/swap/pim/email#>.
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>.
<> session:id "1086926895.725659".
<mid:20040608210620.GC15635@monkeyfist.com> email:date "Tue, 8 Jun 2004 17:06:20 -0400 ";
...

GET -H 'Accept: application/soap-xml' 'http://www.w3.org/Search/Mail/Public/search?keywords=20040608210620.GC15635%40monkeyfist.com&hdr-1-name=subject&hdr-1-query=&index-grp=Public__FULL&index-type=t&type-index=public-rdf-dawg'

and get something (who knows what) in a SOAP envelope:

<?xml version="1.0" encoding="iso-8859-1"?>
<env:Envelope xmlns:env="http://www.w3.org/2003/05/soap-envelope"
   xmlns:email="http://www.w3.org/2000/10/swap/pim/email#"
   xmlns:search="http://www.w3.org/Team/2001/09/search/search.pl#"
   xmlns:session="http://dev.w3.org/cvsweb/perl/modules/W3C/Util/W3CDebugCGI.pm">
 <env:Header>
  <session:id>1086926979.223690</session:id>
 </env:Header>
 <env:Body>
...

The Annotea server behaves similarly.

I can see this working to select between N3 and RDF, even RDF and TRiX
  application/rdf+xml vs application/trix+xml
but not between tuple and graph responses. Those seem like they'd
require different URLs.

On the downside, whatever mime types we need have to be registered
through IETF which puts a dependancy on another orgnanization.

3023 does not deal with compound document, but I don't think we need
that for our purposes. Even if we do, and we have to do something
that's known only to DAWG-QL (or DAWG-TP), we'd have to do that if
we rolled our own format selection protocol.

> I'd be happy to design for 4.4 v. simply[1]:
> 
>     Put a bit in our doc about (1) HTTP content-negotiation and (2)
>     come up with a set of (or a way to generate a set of) canonical
>     names for various serialization formats.
> 
> I believe we'd need to do (2) because, IIRC, the con-neg spec talks
> about IMTs. I just *assume* people are going to use con-neg if we give
> them an HTTP binding for our protocol and don't say anything about all
> of this. Except that then they'll have an interop nightmare because we
> won't have done (2).
> 
> Best,
> Kendall
> 
> [1] What I'd really like to see, vis-a-vis design, is an RDF
> vocabulary to make assertions about the properties of DAWG origin
> servers. The HTTP spec even gives us a very elegant (IMO) discovery
> mechanism using OPTIONS and (slightly extending) OPTIONS *. Such a
> vocabulary could assert which serialization types, identified by URI,
> the server is prepared to offer, as well as other gooey bits of
> metadata-y goodness.

[2] http://www.faqs.org/rfcs/rfc3023.html
-- 
-eric

office: +1.617.258.5741 NE43-344, MIT, Cambridge, MA 02144 USA
cell:   +1.857.222.5741

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Received on Friday, 11 June 2004 00:21:41 GMT

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