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Re: [URI vs. URIViews] draft-frags-borden-00.txt

From: Jonathan Borden <jonathan@openhealth.org>
Date: Fri, 22 Feb 2002 00:45:10 -0500
Message-ID: <031c01c1bb64$19db2300$0301a8c0@ne.mediaone.net>
To: <www-rdf-comments@w3.org>
Cc: "pat hayes" <phayes@ai.uwf.edu>
Pat Hayes wrote:

[[
The critical point to note is that these two senses of 'identify' are
different. The RDF sense is 'denote' or 'refer to'; the RFC 2396
......well, the fact is that RFC 2396 is ambiguous and almost
incoherent, but the sense that is relevant to this discussion is that
it means something like 'identify well enough to locate and retrieve
using a transfer protocol'.
]]

Not sure about that but no matter. Clearly a resource as defined by RFC 2396
and a resource as defined by RDF _are_ different.

>
>RDF, however, uses URIreferences as opaque identifiers for resources and
>this identification is outside any HTTP transaction -- hence no media type
>applies.

[[
This is what Aaron said on the RDF core WG discussion of this
recently. But this seems to me to be confused.  RDF 'uses' them in
this way in the sense that the RDF semantics places no restrictions
on the RDF *interpretation* of a uriref.
]]

No doubt this issue is confused, the only question is as to whom is
confused. But no matter, what I am saying is that the specs are ambiguous
and the attempt is to clarify the usage of the URI + fragment identifier

[[
But that sense is irrelevant
to any other processes that make up the computational fabric of the
web, such as transfer protocols.  I'm sure there are RDF urirefs
which refer to me, but I would be most upset if any kind of web were
to tug my sleeve or call my name when someone clicked on one of them.
]]

Don't conflate a URI with a URL. A URI reference is that: an identifier. No
specific need to actually touch you. That would be a network protocol. See
CPIP (Carrier Pidgeon Internet Protocol) for chuckles.

[[
If we stick to the domain of computable operations on RDF documents,
then RDF's use of fragment ids is quite well-defined and limited: it
uses them to identify *syntactic parts of RDF documents* (typically,
referring IDs located inside RDF assertions inside RDF documents
which have an absolute URI.)
]]

Not just syntactic however, URI reference includes URI '#' fragment
identifier, so an RDF subject predicate, object may contain a fragment
identifier.

[[
So as far as all questions concerning
transfer protocols are concerned, RDF can be considered to *be* a
media type, since at this level of discussion we are talking about
RDF *syntax*, not RDF semantics. Most RDF semantics isn't even
located on the web, in general.
]]

I don't see how you can interpret it this way. I am not talking about any
sort of URI resolution process, simply the use of URI references as subject,
predicate, object. The URI reference need not even be network resolvable
e.g. "urn:uuid:xxxxx"

[[
Well, as long as RDF knows what it identifies, isn't that enough?
]]

I suppose, but if you normatively reference RFC 2396, you are committing to
it. Certainly RDF is self consistent. And if we simply ignore several
convenient definitions all is fine. I have no real problem with this. The
Internet Draft is an attempt to codify this usage by RDF, not argue against
it.

[[
Cf. your HTML/HTTP sketch, above: that seems to work for RDF in just
the same way. The URI is used to retrieve an RDF ontology - a
document -  and the RDF client uses the fragId to identify the term
used in that ontology.
]]

Yes but that is all part of a URI resolution process, which doesn't occur in
RDF applications (mostly). Even if you _do_ assume an RDF media type: what
do you do if you run across a URI reference that doesn't use the RDF media
type registered fragment identifier syntax? (as if one were registered).

>
>See:
>http://www.ietf.org/internet-drafts/draft-borden-frag-00.txt
>
>A generic fragment identifier syntax is defined which encapsulates known
>fragment identifier syntaxes:
>
>The term "sub resource" is introduced, to define what a URI reference
>identifies.

[[
That is meaningless in general, however. Anything can be a resource.
What is a "subresource" of, say, a unicorn or a galaxy? You seem (?)
to be confusing a URL sense of 'resource' meaning: part of a
retrievable web document, with an  RDF/URI sense of 'resource'
meaning: entity referred to by an RDF name.
]]

No. RDF need not concern itself about "sub resources". This term is
introduced in an _IETF_ submitted document to capture an important usage by
RDF of URI references. Again (RDF:resource := IETF:resource union
IETF:subresource)

What is a "subresource" of Unicorn:

suppose the URI http://example.org/Unicorn which identifies the resource
Unicorn
the URI reference http://example.org/Unicorn#LeftButtock identifies the
"subresource"

on the other hand the URI http://example.org/Unicorn/LeftButtock identifies
an (IETF) resource

perhaps they represent the same RDF resource?

[[
(This is the familiar
use/mention confusion that seems to resurface in these discussions
about every six weeks.)
]]

No. It has nothing to do with that. It is a purely definitional issue. An
IETF:resource is defined to be identified by a URI, not a URI reference.
That is really the entire issue.

[[
The resources that RDF *refers* to are,
typically,  not the kind of things that can possibly live on any web
or be transferred by any kind of transfer protocol.
]]

To be clear: IETF resources are not transferred from place to place by
network protocols. A resource is mapped to a network entity (a
representation of the resource) and it is the entity which is teleported
around. See Fielding 2000
http://www1.ics.uci.edu/~fielding/pubs/dissertation/rest_arch_style.htm look
around 5.2.1.1

[[
 The resources
that RDF *uses* are pieces of syntax - ultimately, character strings,
in effect - that can be easily considered to be a mime type or a
media type without straining these concepts unduly.
]]

I disagree. A URI is a piece of syntax. A URI identifies a resource. Where
does it ever say that a resource is a piece of syntax?

[[
RDF *documents*
have parts that are identified by (not referred to by) urirefs with
fragments.
]]

Just to be clear: are you saying that:

<rdfs:Class rdf:ID=:"foo">

...

</rdfs:Class>

The URIref http:// ...#foo identifies the XML element named <rdfs:Class> ?
That is _exactly_ what XML 1.0 says if the attribute "rdf:ID" is defined to
have type ID. What is this RDF stuff then?

What is most interesting is the talk about RDF _assertions_ when the
characteristics of what is being asserted differ so radically despite
assumingly intelligent people reading the exact same documents. Not
something ever likely to hold up in court.

Jonathan
Received on Friday, 22 February 2002 00:25:41 GMT

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