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Re: URI Comparisons: RFC 2616 vs. RDF

From: Nathan <nathan@webr3.org>
Date: Wed, 19 Jan 2011 15:16:31 +0000
Message-ID: <4D37004F.9060404@webr3.org>
To: Dave Reynolds <dave.e.reynolds@gmail.com>
CC: Alan Ruttenberg <alanruttenberg@gmail.com>, public-lod@w3.org
Dave Reynolds wrote:
> On 19/01/2011 3:55 AM, Alan Ruttenberg wrote:
> 
>> The information on how to fully determine equivalence according to the
>> URI spec is distributed across a wide and growing number of different
>> specifications (because it is schema dependent) and could, in
>> principle, change over time. Because of the distributed nature of the
>> information it is not feasible to fully implement these rules.
>> Optionally implementing these rules (each implementor choosing where
>> on the ladder they want to be) would mean that documents written in
>> RDF (and derivative languages) would be interpreted differently by
>> different implementations, which is an unacceptable feature of
>> languages designed for unambiguous communication. The fact that the
>> set of rules is growing and possibly changing would lead to a similar
>> situation - documents that meant one thing at one time could mean
>> different things later, which is also unacceptable, for the same
>> reason.
> 
> Well put, I meant to point out the implications of scheme-dependence and 
> you've covered it very clearly.

Whilst I share the same end goal, I have to stress that *several 
important factors have been omitted*.

The semantic web specifications are not the only ones which affect 
interoperability and compatibility with regard to URIs. Many (most) RDF 
serializations include the use of relative URIs, are affected by base 
mechanisms which are defined by the URIs RFC, dependent on the protocol, 
and by base mechanisms provided by host serialization languages, and 
each of the respective implementations thereof. This covers everything 
from implementations of the http protocol on clients, servers and 
intermediaries, through to implementations of the DOM in XML tooling, 
HTML tooling and the major browsers. It also covers every potential 
component which provides URI support, from open source libraries and 
classes through embedded support in black box applications.

Every single one of the aforementioned are free to (silently) implement 
any of the URI normalization techniques in the URI/IRI RFCs. Each 
implementer of these specifications chooses where on the ladder they 
want to be, and that decision affects & often determines the URIs seen 
by implementations of the semantic web specifications.

These factors cannot be ignored, and they are the factors which the RDF 
specification and semantic web specifications must strive to be 
compatible with, and to normalize the actions of.

Every additional step on the ladder added as a requirement to the RDF 
specification is a step closer to interoperability and compatibility.

>> David (Wood) clarifies (surprisingly to me as well) that the issue of
>> normalization could be addressed by the working group. I expect,
>> however, that any proposed change would quickly be determined to be
>> counter to the instructions given in the charter on Compatibility and
>> Deployment Expectation, and if not, would be rejected after justified
>> objections on this basis from reviewers outside the working group.
> 
> +1

As per the above, I'd expect the polar opposite.

+1 to compatibility (with the real, deployed, web - the one we all use)

Best,

Nathan
Received on Wednesday, 19 January 2011 15:18:30 UTC

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