- From: Williams, Stuart (HP Labs, Bristol) <skw@hp.com>
- Date: Tue, 15 Jan 2008 11:51:56 +0000
- To: Alan Ruttenberg <alanruttenberg@gmail.com>
- CC: "public-awwsw@w3.org" <public-awwsw@w3.org>
FWIW I think that the advent of GRDDL and RDFa bring up a number of issues related to base URI and same document references.
+--------+ +---------------+
| | Representation | Client-Side | Transformed Representation
| origin +-------------------->+ GRDDL/RDFa |------------------>
| server | Media Type: #1 | Transformation| Media Type: #2
| | Base URI: #1 | | Base URI: #2
+--------+ +---------------+
Pre-GRDDL/RDFa the contradiction you cite in the example below could not have arisen.
With care, I believe - though have not tried, a document author can arrange for the triples that they 'want' to come out of the transform, though that may involve specifying absolute URI in the relevant places of the document.
It seems to me that there are two dispositions one can take wrt to the authoring of an RDFa or GRDDL'able document.
1) Given an RDF graph, how does an author embed that graph in the document in such away that the transformed representation is a representation of that graph.
2) Given an RDFa/GRDDLable document, what triple happen to arise when it is transformed.
The first disposition is centred around authors intent, while the latter is centred around what an observer my attempt to glean from the document - and without care the two may diverge.
In respect of the example below: clearly http://sw-app.org/mic.xhtml#i cannot be the URI of a piece of document serialisation and the URI of a person.
IMO the HTML and RDF media types are incompatible for mixing in this way. The RDF media-type has an inherent "thing-described-by" indirection whereas the HTML media type does not. I can only see the representation and transformed representation as being consistent where either a given anchor (ID or rdf:ID) appear in only one or the RDF assertions are indeed about the relevant parts of the document.
In this case... how would the contradiction be detected?
http://sw-app.org/mic.xhtml contains the following served as: application/xhtml+xml
<div id="i" instanceof="foaf:Person" about="http://sw-app.org/mic.xhtml#i">
<p>
My name is <span property="foaf:name" datatype="xsd:string">Michael Hausenblas</span>
(also known as <span property="foaf:nick">mic.</span>) and
I work at <a href="http://www.joanneum.at/iis/" rel="foaf:workplaceHomepage">JOANNEUM RESEARCH</a> in the field of media semantics.
If you are interested in further details, you may also want to visit my
<a rel="foaf:homepage" href="http://sw-app.org/about.html">private homepage</a>
or read my <a rel="foaf:homepage" href="http://mhausenblas.blogr.com">blog</a>.
</p>
<div class="centerArea">
<img src="http://sw-app.org/img/mic_2007_01.jpg" rel="foaf:depiction" alt="Picture of Michael Hausenblas, 2007" href="http://sw-app.org/img/mic_2007_01.jpg"/>
</div>
<h2>Business Contact</h2>
<div rel="foaf:office">
<span rel="foaf:address">
<span property="foaf:street">Steyrergasse 17</span><br />
<span property="foaf:postalCode">8020</span> <span property="foaf:city">Graz</span> <br />
<span property="foaf:country">Austria</span><br />
<span property="foaf:phone">tel:+43-(316)-876-1193</span><br />
<span property="foaf:mail" datatype="xsd:string"><a href="mailto:michael.hausenblas@joanneum.at">michael.hausenblas@joanneum.at</a></span>
</span>
</div>
The contradiction arises in the very first line where 'id="i"' introduces an anchor whose URI, given the document base URI is <http://sw-app.org/mic.xhtml#i>.
Implicit in the application/xhtml+xml media-type is that that URI identifies a part of the document - some background rule is needed somewhere to be able to say that ie.
<http://sw-app.org/mic.xhtml#i> a webarch:DocumentFragment .
Ironically, maybe, the 'about="http://sw-app.org/mic.xhtml#i"' attribute in the same element which establishes the subject of the RDF assertions emitted in the transformed representation is given in full (and could have been for a different subject URI).
In concept at least, the domain constraints (assuming they are stated in the FOAF ontology - I haven't checked) on the foaf properties used license an inference that:
<http://sw-app.org/mic.xhtml#i> a foaf:Person .
That foaf:Person and webarch:DocumentFragment are disjoint needs to be a seperately stated piece of background knowledge in order for a reasoner to detect the contradiction.
IMO it comes down to an author deciding what they *want* the URIs they create to stand for. In this case a change to the first line of either
<div id="me" instanceof="foaf:Person" about="http://sw-app.org/mic.xhtml#i">
or
<div id="i" instanceof="foaf:Person" about="http://sw-app.org/mic.xhtml#mic">
would avoid this particular contradiction, establishing separate URI for document fragment and person (only the latter of which propagates to the RDF - I think) - modulo other assertions which may contribute to contradictions in other ways.
A simpler Lint-like check that flags up when 'id' and 'about' attributes on the same element resolve to the same URI would pick up a great many situations where the authors intent is unclear.
BR,
Stuart
--
Hewlett-Packard Limited registered Office: Cain Road, Bracknell, Berks RG12 1HN
Registered No: 690597 England
________________________________
From: public-awwsw-request@w3.org [mailto:public-awwsw-request@w3.org] On Behalf Of Alan Ruttenberg
Sent: 30 December 2007 00:06
To: public-awwsw@w3.org
Subject: What inferences should be made
The contradiction noted below would be a candidate for one sort of thing we would like to detect.
-Alan
Begin forwarded message:
Resent-From: semantic-web@w3.org
From: Richard Cyganiak <richard@cyganiak.de>
Date: December 28, 2007 8:21:45 AM EST
To: Leo Sauermann <leo.sauermann@dfki.de>
Cc: "Hausenblas, Michael" <michael.hausenblas@joanneum.at>, Leo Sauermann <sauermann@dfki.uni-kl.de>, semantic-web@w3.org
Subject: Re: Cool URIs, the Semantic Web and Everything
Archived-At: <http://www.w3.org/mid/D5C350C2-E110-4672-926D-28373DAAA4B7@cyganiak.de>
On 25 Dec 2007, at 21:41, Leo Sauermann wrote:
[snip]
Q.II: What does http://sw-app.org/mic.xhtml#i identfiy?
[snip]
This is impossible to answer, because the URI's configuration is broken. Even the author of the document seems to be confused about what he wants the URI to identify.
There is an XHTML representation, and it has a id="i", which indicates that the URI identifies an XHTML fragment.
But the XHTML document also encodes an RDF graph using RDFa. In it, the author tries to use the same URI to denote a person. He claims that a document fragment is a person. That's a nonsensical statement.
Fortunately, this is easy to fix: Remove the id="i" from the document, or change it to a different ID, and everything is fine. After that fix, the answer would be 1, 2 and 6.
I don't know about removing the ID, maybe this would be good. But I would not make a "must" out of it, why not keep both
The application/xhtml+xml MIME type registration says: If there is @id="i" in the XHTML document, then <mic.xhtml#i> designates a part of that document. Thus, web architecture clearly states that <mic.xhtml#i> identifies a document part.
Michael's RDFa, however, says that <mic.xhtml#i> denotes a person.
That's a contradiction. A person is not a section of a document. Therefore, the @id="i" *MUST* be changed or removed, otherwise we have a URI collision.
Richard
best
Leo
Cheers,
Michael
----------------------------------------------------------
Michael Hausenblas, MSc.
Institute of Information Systems & Information Management
JOANNEUM RESEARCH Forschungsgesellschaft mbH
Steyrergasse 17, A-8010 Graz, AUSTRIA
----------------------------------------------------------
-----Original Message-----
From: Richard Cyganiak [mailto:richard@cyganiak.de]
Sent: Friday, December 21, 2007 5:26 PM
To: Hausenblas, Michael
Cc: Leo Sauermann; semantic-web@w3.org; Leo Sauermann
Subject: Re: Cool URIs, the Semantic Web and Everything
Michael,
On 21 Dec 2007, at 08:23, Hausenblas, Michael wrote:
In Cool URIs you are
referring to a certain
setup ('deployment scenarios in which the RDF data and the
HTML data
is served separately').
Also the figure right before section 3.1 suggests that there is an
explicit RDF document and an HTML document, each with a
distinct URL.
As you know, this is not the case with RDFa.
Would changing the sentence
"In those cases [RDFa, microformats and GRDDL] the RDF data
is extracted from the returned HTML document."
to
"In those cases, the RDF data is extracted from the HTML
document and no separate RDF document is needed."
address your complaint?
The rest of the document's narrative is consistent with use
of RDFa, as far as I can tell.
Best,
Richard
So, that is were my confusion stems from. I know that due to time
constraints you decided that this is the way it is. It
would still be
nice to learn why the figure right before section 3.1
(sorry, no label
available) 'shows the desired relationships between a
resource and its
describing documents'.
Cheers,
Michael
[1]
http://lists.w3.org/Archives/Public/semantic-web/2007Dec/0121.html
----------------------------------------------------------
Michael Hausenblas, MSc.
Institute of Information Systems & Information Management JOANNEUM
RESEARCH Forschungsgesellschaft mbH
http://www.joanneum.at/iis/
----------------------------------------------------------
-----Original Message-----
From: Leo Sauermann [mailto:sauermann@dfki.uni-kl.de]
Sent: Thursday, December 20, 2007 12:36 PM
To: Hausenblas, Michael
Cc: semantic-web@w3.org; Leo Sauermann
Subject: Re: Cool URIs, the Semantic Web and Everything
Hausenblas, Michael schrieb:
Leo,
Thanks for your explanation. I remain not totally convinced :)
good, then give a practical example (using concrete RDFa
code) where
you think some work needs to be done and provide a
suggestion how to
solve it. That you are not convinced may be caused by
various reasons
we don't know about, shine light on them.
So, *if* we agree on what you said, IMHO we should
reconsider the following paragraph in 'Cool URIs' [1]:
'The solutions described in the following apply to deployment
scenarios
in which the RDF data and the HTML data is served
separately, such
as a
standalone RDF/XML document
along with an HTML document. The metadata can also be
embedded in
HTML,
using technologies such as
RDFa [RDFa Primer], microformats and other documents to
which the
GRDDL
[GRDDL] mechanisms can be applied.
In those cases the RDF data is extracted from the returned HTML
document.'
I see no reason for changes until you exactly specify where this
paragraph contradicts http-range-14 or other TAG
resolutions or W3C
recommendations.
the point is that RDF/XML, N3, RDFa and GRDDL are
mimetypes encoding
RDF triples while URIs are something used inside these RDF
triples,
so at the beginning both are completly different and do not affect
each other.
"Cool uris" is about URIs and not about RDF serialization.
best
Leo
Still unsure if this is just the tip of the iceberg ...
Cheers,
Michael
[1] http://www.w3.org/TR/2007/WD-cooluris-20071217/#solutions
----------------------------------------------------------
Michael Hausenblas, MSc.
Institute of Information Systems & Information Management
JOANNEUM RESEARCH Forschungsgesellschaft mbH
http://www.joanneum.at/iis/
----------------------------------------------------------
-----Original Message-----
From: Leo Sauermann [mailto:sauermann@dfki.uni-kl.de]
Sent: Thursday, December 20, 2007 3:43 AM
To: Hausenblas, Michael
Cc: semantic-web@w3.org; Leo Sauermann
Subject: Re: Cool URIs, the Semantic Web and Everything
Hi Michael, RDFa people,
The question is if httpRange-14 [2] is valid in
the case of
XHTML+RDFa.
The answer is that httpRange-14 is to
distinguish URIs for
information
resources ("web documents") from real-world
objects (the person
"Alice"). As such, it is a recommendation on URIs.
RDFa is an encoding of RDF, and typically an
RDFa document has two
relations to URIs:
a) the URI of the RDFa document (=the
information resource where I
can
download the RDFa document)
b) the URIs used as subjects, predicates,
objects inside RDF
statements
written inside RDFa documents
a) is usually a http-200 uri, and a) is an
information resource (=
a
document).
In the rdf statemetns written inside A, you
would use both URIs
for
real-world objects and information resources.
example (I don't know rdfa syntax by heart
now, assume this is
rdfa):
document at www.example.com/homepage/aboutAlice
<html>
<p
rdf:about="http://www.example.com/identifiers/alice#this"
<http://www.example.com/identifiers/alice#this> >
rdf:type foaf:Person.
</p>
<p
rdf:about="http://www.example.com/moreidentifiersusing303/bob"
<http://www.example.com/moreidentifiersusing303/bob> >
rdf:type foaf:Person
</p>
</html>
assuming this would be valid RDFa, the URI
.../aboutAlice is a
http-return-200 informaiton resource
.../alice#this is a real-world object as it is
not a document (as I
understand timbl on that)
...303/bob is not intuitively distinguishable -
if you ignore the
rdf:type relation you don't know what it is. So
for this uri you do
a
HTTP get and the server would return a 303
redirect as described in
"cool uris".
once oyu did the 303, you knowthat ....303/bob
is a real world
object.
so RDFa and 303'/httprange14 are
recommendations caring about
different
angles, 303 is only concerned about URIs, RDFa
about an RDF
serialization. Technically they don't interfere.
If I would use RDFa much and would like cool
uris, I would go for
#-uris, they are simple to use and easy to
embed in RDFa.
but as shown above, you can use any URI you
want inside rdfa.
best
Leo
Hausenblas, Michael schrieb:
===
Disclaimer: Michael, with his
RDFa-Task-Force-member hat off ;)
===
As I gathered "Cool URIs for the
Semantic Web" is a Working
Draft, now.
Congrats to Leo and his team, great job!
The following might sound like a naive
question - and I might
have missed something :) - but: Is TAG
finding httpRange-14 [2]
equally valid in the case of XHTML+RDFa?
I've put together some initial thoughts
at the ESWiki [3]
- any comments welcome!
Cheers,
Michael
[1]
http://lists.w3.org/Archives/Public/public-swd-wg/2007Dec/0103.html
[2]
http://www.w3.org/2001/tag/issues.html#httpRange-14
[3] http://esw.w3.org/topic/RDFa_vs_RDFXML
----------------------------------------------------------
Michael Hausenblas, MSc.
Institute of Information Systems &
Information Management
JOANNEUM RESEARCH Forschungsgesellschaft mbH
Steyrergasse 17, A-8010 Graz, AUSTRIA
<office>
phone: +43-316-876-1193 (fax:-1191)
e-mail: michael.hausenblas@joanneum.at
web: http://www.joanneum.at/iis/
<private>
mobile: +43-660-7621761
web: http://www.sw-app.org/
----------------------------------------------------------
--
____________________________________________________
DI Leo Sauermann http://www.dfki.de/~sauermann
Deutsches Forschungszentrum fuer Kuenstliche Intelligenz DFKI GmbH
Trippstadter Strasse 122
P.O. Box 2080 Fon: +49 631 20575-116
D-67663 Kaiserslautern Fax: +49 631 20575-102
Germany Mail: leo.sauermann@dfki.de
Geschaeftsfuehrung:
Prof.Dr.Dr.h.c.mult. Wolfgang Wahlster (Vorsitzender)
Dr. Walter Olthoff
Vorsitzender des Aufsichtsrats:
Prof. Dr. h.c. Hans A. Aukes
Amtsgericht Kaiserslautern, HRB 2313
____________________________________________________
Received on Tuesday, 15 January 2008 11:54:05 UTC