W3C home > Mailing lists > Public > semantic-web@w3.org > June 2012

Re: Semantic URI Syntax

From: Michael Hausenblas <michael.hausenblas@deri.org>
Date: Wed, 27 Jun 2012 11:01:49 +0100
Cc: Semantic Web <semantic-web@w3.org>
Message-Id: <D5085E03-B70D-42A0-AA31-9E192063990E@deri.org>
To: Martin Hepp <martin.hepp@ebusiness-unibw.org>, David Sheets <sheets@alum.mit.edu>

>> Is this scheme-dependent?
> From the top of my head, the hash fragment is defined for HTTP and HTTPS URIs only.


The Generic URI syntax spec [1] tells us:

[[
The semantics of a fragment identifier are defined by the set of representations that might result from a retrieval action on the primary resource. The fragment's format and resolution is therefore dependent on the media type RFC2046 of a potentially retrieved representation, even though such a retrieval is only performed if the URI is dereferenced. If no such representation exists, then the semantics of the fragment are considered unknown and are effectively unconstrained. Fragment identifier semantics are independent of the URI scheme and thus cannot be redefined by scheme specifications.
]]

HTH.

Cheers,
	   Michael

[1] http://tools.ietf.org/html/rfc3986#section-3.5

--
Dr. Michael Hausenblas, Research Fellow
DERI - Digital Enterprise Research Institute
NUIG - National University of Ireland, Galway
Ireland, Europe
Tel.: +353 91 495730
WebID: http://sw-app.org/mic.xhtml#i

On 27 Jun 2012, at 10:26, Martin Hepp wrote:

> 
> On Jun 26, 2012, at 8:54 PM, David Sheets wrote:
> 
>> Hello,
>> 
>> I am working on a semanticization of WebGL shaders [1] and I have a
>> few questions regarding URI syntax conventions.
>> 
>> 1. Let <URI> be an absolute URI without fragment. Is (<URI> == <URI>#)
>> true?
> No. URIs as identifiers are equivalent only when they are the same, character by character. Only very few encoding variants may be treated as equal by some RDF implementations.
>> Is this scheme-dependent?
> From the top of my head, the hash fragment is defined for HTTP and HTTPS URIs only.
> 
>> What level of normalization is this?
> This I don't understand.
>> Is this question answered somewhere online already?
>> 
> 
> For URIs in the context of HTTP, RFC 2616, Section 3.2.3 (http://www.ietf.org/rfc/rfc2616.txt) is the authoritative spec:
> 
> "
> 
> 3.2.3 URI Comparison
> 
>   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"
> 
> 
> This is for using URIs as locators. Note that for the use of identifiers in RDF, even those limited transformations will not be carried out, thus creating different identifiers.
> 
> A comprehensive discussion on URI comparison in the Semantic Web is e.g. in the mailing list archive, starting with
> 
> http://lists.w3.org/Archives/Public/public-lod/2011Jan/0134.html
> 
> 
> 
> Martin
> 
>> 
> 
> 
> 
> --------------------------------------------------------
> martin hepp
> e-business & web science research group
> universitaet der bundeswehr muenchen
> 
> e-mail:  hepp@ebusiness-unibw.org
> phone:   +49-(0)89-6004-4217
> fax:     +49-(0)89-6004-4620
> www:     http://www.unibw.de/ebusiness/ (group)
>         http://www.heppnetz.de/ (personal)
> skype:   mfhepp 
> twitter: mfhepp
> 
> Check out GoodRelations for E-Commerce on the Web of Linked Data!
> =================================================================
> * Project Main Page: http://purl.org/goodrelations/
> 
> 
> 
> 
Received on Wednesday, 27 June 2012 10:02:20 GMT

This archive was generated by hypermail 2.3.1 : Tuesday, 26 March 2013 21:45:49 GMT