On 1/17/11 12:27 PM, Nuno Bettencourt wrote:
Hi,
Even though I'll be deviating the point just a bit, since we're discussing URI
comparison in terms of RDF, I would like to request some help.
I have a doubt about URLs when it comes to RDF URI comparison. Is there any RFC
that establishes if
http://abc.com:80/~smith/home.html
https://abc.com:80/~smith/home.html
or even
ftp://abc.com:80/~smith/home.html
should or not be considered the same resource?
All of the above are Addresses (based on what I can infer via my visual
senses). The URI abstraction enables multiple scheme data access. "ftp:"
and "http:" are schemes. None of them isA resource. They simply provide
access to data why may be serialized in a variety of formats to a user
agent that de-references any of these Addresses. Basically, network
aware pointers with data representation dexterity courtesy of URI
abstraction and HTTP's content negotiation.
Kingsley
Best regards,
Nuno Bettencourt
-----Original Message-----
From: public-lod-requ...@w3.org [mailto:public-lod-requ...@w3.org] On
Behalf Of Nathan
Sent: segunda-feira, 17 de Janeiro de 2011 16:53
To: Dave Reynolds; Sandro Hawke
Cc: Martin Hepp; public-lod@w3.org
Subject: Re: URI Comparisons: RFC 2616 vs. RDF
Dave Reynolds wrote:
On Mon, 2011-01-17 at 16:51 +0100, Martin Hepp wrote:
Dear all:
RFC 2616 [1, section 3.2.3] says that
"When comparing two URIs to decide if they match or not, a client
SHOULD use a case-sensitive octet-by-octet comparison of the entire
URIs, with these exceptions:
- A port that is empty or not given is equivalent to the default
port for that URI-reference;
- Comparisons of host names MUST be case-insensitive;
- Comparisons of scheme names MUST be case-insensitive;
- An empty abs_path is equivalent to an abs_path of "/".
Characters other than those in the "reserved" and "unsafe" sets (see
RFC 2396 [42]) are equivalent to their ""%" HEX HEX" encoding.
For example, the following three URIs are equivalent:
http://abc.com:80/~smith/home.html
http://ABC.com/%7Esmith/home.html
http://ABC.com:/%7esmith/home.html
"
Does this also hold for identifying RDF resources
a) in theory and
No. RDF Concepts defines equality of RDF URI References [1] as simply
character-by-character equality of the %-encoded UTF-8 Unicode strings.
Note the final Note in that section:
"""
Note: Because of the risk of confusion between RDF URI references that
would be equivalent if derefenced, the use of %-escaped characters in
RDF URI references is strongly discouraged.
"""
which explicitly calls out the difference between URI equivalence
(dereference to the same resource) and RDF URI Reference equality.
I'd suggest that it's a little more complex than that, and that this may be an
issue to clear up in the next RDF WG (it's on the charter I believe).
For example:
When a URI uses components of the generic syntax, the component
syntax equivalence rules always apply; namely, that the scheme and
host are case-insensitive and therefore should be normalized to
lowercase. For example, the URI<HTTP://www.EXAMPLE.com/> is
equivalent to<http://www.example.com/>.
- http://tools.ietf.org/html/rfc3986#section-6.2.2.1
However, that's only for URIs which use the generic syntax (which most URIs
we ever touch do use).
It would be great if a normalized-IRI with specific normalization rules could be
drafted up as part of the next WG charter - after all they are a pretty pivotal
part of the sem web setup, and it would be relatively easy to clear up these
issues.
Best,
Nathan
--
Regards,
Kingsley Idehen
President& CEO
OpenLink Software
Web: http://www.openlinksw.com
Weblog: http://www.openlinksw.com/blog/~kidehen
Twitter/Identi.ca: kidehen
