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Re: [ISSUE 57] Representation-source: a possible new approach to the HTTP Redirection Issue

From: Danny Ayers <danny.ayers@gmail.com>
Date: Mon, 25 Feb 2008 13:52:03 +0100
Message-ID: <1f2ed5cd0802250452m4d4d8b1dq1900f95312afebc7@mail.gmail.com>
To: "Roy T. Fielding" <fielding@gbiv.com>
Cc: noah_mendelsohn@us.ibm.com, "W3C TAG" <www-tag@w3.org>

While they seem an interesting and potentially useful notion, I don't
think Noah's Immutable Document Resources offer any practical help to
the underlying problem. In fact, HttpRedirections-57 itself seems
rather back-to-front, largely addressing potential solutions rather
than starting back at the underlying question (yeah, ok, this is going
back to httpRange-14 a bit).

So here's my two cents. I suggest we forget trying to find a purely
technical solution and just use a slightly different abstraction
around what it means to be on the Web versus on the Semantic Web. It
seems to me that if we take into consideration different kinds of
consumer capability, the problem evaporates. Key to this I think is
looking at what a link means in different contexts. (The practical
upshot of what I suggest would be that a HTTP 200 is an option
available for *all* kinds of resources, though publishers may choose
to use the 303 redirect for resources where it's convenient).

Roy asks whether "A key requirement of the Semantic Web is that URIs
be used to identify resources unambiguously". Well, yes, I'd suggest
it is, in exactly the same way the Web is dependent on an essentially
unambiguous naming scheme - the resource identified and the URI are
intimately bound, thanks to their somewhat circular, fixpoint kind of
definition. On the other hand the relationship between a resource and
the thing it stands for does have ambiguity - the publisher may be
clear, but the consumer of such information is limited to making their
best interpretation of whatever (ultimately human-readable)
definitions the publisher has provided.

But I think Roy does highlight the most important part of the issue
when he says:
[[
On the Web, millions of people mint URIs, and millions more use them
in references. Millions of human beings, conversing over time, with an
occasional URI thrown in to refer to a subject under discussion.
]]

Ok, the Semantic Web is an extension of the existing
(document-oriented) Web. Flipping that over, I think it's reasonable
to consider the existing Web as a projection or view of (some subset
of) the Semantic Web.

>From this perspective, regular HTML links can been seen as expressions
of (s, p, o) statements, where the predicate isn't explicitly typed.
The relation can be typed, using the rel/rev attributes in concert
with a HTML Meta Data profile - GRDDL is the nearest we have to a
formalism for this. But it's common practice to use a kind of
human-friendly implicit typing, for example using <a
href="http://www.ics.uci.edu/~fielding/">Roy Fielding</a> to refer to
a person.

But I'm suggesting the Semantic Web *does* need to distinguish between
Roy the person and Roy's homepage. A reasonable RDF expression of the
link above might be something like:

<> dc:related <http://www.ics.uci.edu/~fielding/> .
[ foaf:name "Roy Fielding";
  foaf:homepage <http://www.ics.uci.edu/~fielding/> ] .

But does the (document) Web need to distinguish between Roy the person
and Roy's homepage? Evidently not, given the utility of simple linkage
like that above.

The only way I can see to square this circle is to differentiate
between two kinds of interpretation. For example:

$ wget http://www.w3.org/People/Berners-Lee/card.n3#i
...
HTTP request sent, awaiting response... 200 OK

Web interpretation: this is somehow related to Tim
Semantic Web interpretation: we got a 200, so this is about Tim - what
does the RDF here say?

If we'd got a 303, sure, we could follow the httpRange-14 resolution's
interpretation. But I don't think we can realistically assume
200=Information Resource. I don't think this problem can be completely
resolved with a technical trick at the HTTP layer.

When I talk of "the Semantic Web" and "the Web" above I'm really using
shorthand for "the consumer is armed with SW tools" and "the consumer
only has document-oriented tools". Heuristics may provide RDF
interpretations of material that hasn't been published with those
interpretations in mind (like using dc:related or rdfs:seeAlso for
HTML links), and browser rendering (e.g. as text) may provide
document-oriented interpretations of material solely intended for
machine consumption.

When we get Tim's FOAF profile, it's possible to delve deeper with
RDF-aware software than it is with RDF-unaware software. In other
words, the Web only understands Information Resources. You need an
expanded conceptual infrastructure to tease the description of a
person in RDF statements from the "pre-Semantic" representation.

This approach does look like content sniffing - but I don't think that
really applies, it's more like: to find out about a resource, as well
as following your nose, you might also need to use your eyes.

Cheers,
Danny.

[1] http://roy.gbiv.com/untangled/2008/resource-resource-wherefore-art-thou-resource

-- 
http://dannyayers.com
~
http://blogs.talis.com/nodalities/this_weeks_semantic_web/
Received on Monday, 25 February 2008 12:52:24 GMT

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