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RE: [metaDataInURI-31]: Initial draft finding for public review/c omment.

From: Williams, Stuart <skw@hp.com>
Date: Fri, 11 Jul 2003 17:18:34 +0100
Message-ID: <5E13A1874524D411A876006008CD059F04A07627@0-mail-1.hpl.hp.com>
To: "'Patrick.Stickler@nokia.com'" <Patrick.Stickler@nokia.com>, "Williams, Stuart" <skw@hp.com>, MDaconta@aol.com
Cc: www-tag@w3.org

> There is certainly a gray area, in the case where URI schemes 
> impose restrictions on the kinds of resources that should be 
> denoted by instances of those URI schemes. Likewise for any 
> subschemes, etc.
> 
> That someone would be able to infer an rdf:type assertion 
> based on a URI scheme is logical, and I wouldn't necessarily 
> fault a particular application from doing so.
> 
> But the number of URI schemes that have such explicit 
> extensions are few, and so it does not seem worthwhile to 
> make such inferences a regular part of the overall web architecture.
> 
> And since such cases can be addressed just as well by URIQA, 
> why introduce yet another, less general, less flexible, less 
> scalable, and less robust mechanism for publishing knowledge 
> about resources?

I could be quite happy with a 'don't peek inside URIs' position. I am trying
to reconcile that with things that other folks seem to want to do... eg.
make assertions about the nature of things identified by http scheme URIs
that contain a fragment component. I don't think we can have it both ways.
The 'middle' ground I was shooting for was allowing ourselves to use
whatever is stated in the relevant (narrative) specifications. I agree that
this doesn't scale. There will be schemes that on manifestly does not know
about or chooses not to implement - and in such cases the URI are truly
opaque beyond separating out scheme, hier-part (RFC2396bis), query and
fragment components.

Regards

Stuart
--

> -----Original Message-----
> From: Patrick.Stickler@nokia.com [mailto:Patrick.Stickler@nokia.com] 
> Sent: 10 July 2003 12:42
> To: skw@hp.com; MDaconta@aol.com
> Cc: www-tag@w3.org
> Subject: RE: [metaDataInURI-31]: Initial draft finding for 
> public review/comment.
> 
> 
> 
> -----Original Message-----
> From: ext Williams, Stuart [mailto:skw@hp.com]
> Sent: 09 July, 2003 15:08
> To: Stickler Patrick (NMP/Tampere); MDaconta@aol.com
> Cc: www-tag@w3.org
> Subject: RE: [metaDataInURI-31]: Initial draft finding for 
> public review/comment.
> 
> 
> For me part of the question is when I (or a piece software I 
> might write) look at a URI (assigned by someone else), what 
> do I allow myself to know (intrinsically from examining the 
> URI rather than going without asking an authority)? (BTW 
> "Nothing" is an acceptable answer). Do I allow myself access 
> to the knowledge embedded in a bunch of normative 
> specifications (and possibly published assignment policies)?
> 
> At one time, I was a big proponent of "peeking" into URIs to deduce 
> knowledge about the resource denoted, as there did not appear 
> any other reliable, standardized, and globally ubiquitous manner of 
> obtaining fundamental knowledge about resources.
> 
> You may even recall back a couple of years when I was 
> exploring various means to do this via a more regular and 
> well defined ontology for classifying and relating URI schemes.
> 
> After a good bit of thought and work, it became evident that
> a more general solution was needed. And that work lead to URIQA.
> 
> It is very true that at some stage, an agent is going to have 
> to examine the lexical properties of the URI to apply any 
> protocols or processes defined in terms of the URI scheme, 
> any subscheme, and its structure.
> 
> But given the function of URIs as identifiers, I am now of 
> the opinion that any knowledge that might be encapsulated in 
> the URI should be justified by the needs of identification, 
> not of description.
> 
> For description, more open methods such as URIQA which are
> not limited either by URI structural constraints nor the need 
> (or at least desire) for persistant URIs.
> 
> 
> Do I allow myself to know that the URI mailto:skw@hp.com 
> identifies an "Internet mailing address", because RFC2396 
> (and successors) allow me to identify a scheme component and 
> RFC2368 as the registered scheme specification for the mailto 
> URI scheme tells me "The mailto URL scheme is used to 
> designate the Internet mailing  address of an individual or 
> service". IMO, if I allow myself to know that 
> mailto:skw@hp.com identifies an "Internet mailing address" 
> then I have 'peeked', allbeit at only the scheme component. 
> Likewise for other URI schemes that state the sort of thing 
> that they are used to identify. Some would say, "No, you 
> don't allow yourselve to know such things... don't peek, URI 
> are opaque (to a web client)." Others want to build rule 
> driven systems that very much depend allowing such 
> inferences... and it was only a little peek... hardly a peek 
> at all... (maybe).
> 
> There is certainly a gray area, in the case where URI schemes 
> impose restrictions on the kinds of resources that should be 
> denoted by instances of those URI schemes. Likewise for any 
> subschemes, etc.
> 
> That someone would be able to infer an rdf:type assertion 
> based on a URI scheme is logical, and I wouldn't necessarily 
> fault a particular application from doing so.
> 
> But the number of URI schemes that have such explicit 
> extensions are few, and so it does not seem worthwhile to 
> make such inferences a regular part of the overall web architecture.
> 
> And since such cases can be addressed just as well by URIQA, 
> why introduce yet another, less general, less flexible, less 
> scalable, and less robust mechanism for publishing knowledge 
> about resources?
> 
> Another example, that links with the httpRange-14 debate. One 
> position in that debate is that http scheme URIs without 
> fragment identifiers may only be used to identify network 
> accessible resources, and may not be used to identify 
> abstract concepts (eg. a particular emotion) or a real-world 
> object (like DanC's car or a person) eg. using 
> http://people.example.com/stuart to identify me would be 
> frowned upon.  
> 
> I personally take the opposing view, and find the use of URIs 
> with fragment identifiers to be unwise and problemmatic, and 
> see no reason, technical, philosophical, or practical which 
> would warrant any such restriction from using http: URIs to 
> denote any entity whatsoever that can be named and thus referred to.
> 
> One of the greatest contributions provided by REST is the 
> abstraction away from "files" or "streams of bytes" allowing 
> URIs to consistently denote a resource (any resource, even 
> Dan C's car) irrespective of 
> whether such resources are bit equal to their representations.
> 
>  However, within this particular position, it is ok to 
> identify abstract concepts and real world artifacts with http 
> scheme URIs that include a fragment identifier ie. 
> http://people.example.com#stuart would be fine. If we were to 
> accept this particular position, then the presense or absense 
> of a fragment component (even a null fragment) in an http URI 
> allows an inference to be made about whether the referenced 
> resource is a network accessible resource or an abstract 
> concept or real-world thing. Some folks want to build systems 
> that rely on such distinctions... and IMO this again is peeking. 
> 
> I agree. And I would assert that the position that only URIs 
> having fragment identifiers can denote non-digitized 
> resources is (a) already rejected by common 
> usage (b) unnecessarily and IMO unjustifiably restrictive, 
> and (c) unsupported by and contrary to the present definition 
> of HTTP, which requires web clients to omit the fragment ID 
> from requests. After all, if the fragment ID is disposable in 
> a transaction between client and server, how can it be the 
> basis for the semantic web, since the identity of the actual 
> resource denoted by the URIref with fragid is lost?
> 
> So any inferences that one may presume to derive from the 
> presence or absence of a fragid will be suspect at best, and 
> with the advent of URIQA, unnecessary in any case.
> 
> "Don't peek inside URI's" is a very simple thing to say and 
> to understand, but I think that even amongst those that might 
> say it there is a temptation to peek - with good reason - so 
> as a prinicple it may be a little to simplistic.
> 
> I'm not going to take an absolutist view about peeking into 
> URIs. I'm a pretty pragmatic and practical person. It's not a 
> question of recommending "Don't do this" so much as it is a 
> question of  actually recommeding "Do it"  as a general methodology.
> 
>  Peeking inside URIs will IMO always be plagued with 
> problems, because many/most of the generalities that are 
> percieved in the structure of URIs are not absolute, and 
> hence not reliable.
> 
> Better to emphasize/promote/optimize methods of publishing
> and accessing knowledge that is expressed in an explicit 
> manner and governed by a consistent and well defined model theory.
> 
> Over time, I think, the need for specialized URI schemes will 
> decrease, as will the amount of knowledge packed into URIs in 
> general, as technologies such as URIQA become ubiquitous.
> 
> Cheers,
> 
> Patrick
> 
> 
> Stuart
> --
> 
> -----Original Message-----
> From: Patrick.Stickler@nokia.com [mailto:Patrick.Stickler@nokia.com] 
> Sent: 9 July 2003 10:13
> To: MDaconta@aol.com; skw@hp.com; www-tag@w3.org
> Subject: RE: [metaDataInURI-31]: Initial draft finding for 
> public review/comment.
> 
> 
> 
> -----Original Message-----
> From: ext MDaconta@aol.com [mailto:MDaconta@aol.com]
> Sent: 08 July, 2003 21:11
> To: skw@hp.com; www-tag@w3.org
> Subject: Re: [metaDataInURI-31]: Initial draft finding for 
> public review/comment.
> 
> 
> In a message dated 7/8/2003 6:44:46 AM US Mountain Standard 
> Time, skw@hp.com writes:
> 
> 
> I would appreciate some feedback on this draft. Whether a 
> simpler, shorter, finding is a better path to take? Whether 
> "Don't peek inside URIs" is all that need be said?
> 
> 
> 
> Hi Stuart,
> 
> First, to answer your questions:
> 1. A simpler and shorter finding is only better for the 
> "don't peek inside" position. 2. I disagree with the "Don't 
> peek inside URIs" sentiment.  
> 
> The "Don't peek inside" position stresses the use of 
> identification as an assertion of 
> uniqueness and possibly a mechanism to locate that unique 
> thing.  In essence, 
> an opaque "pointer".  While those are necessary functions of a URI, 
> imbuing an identifier with additional metadata should be 
> encouraged.  First, additional metadata in a URI makes it 
> easier to keep the URI "cool" (as in 
> http://www.w3.org/Provider/Style/URI.html) by > adding 
> classification metadata to the identifier (as with the W3C 
> URLs in your 
> finding). 
> 
> What if the metadata changes? Then you have a different URI, 
> and things break.
> 
> URIs with metadata embedded in them which might change are 
> hardly "cool".
> 
> Second, additional metadata in a URI enables a higher-level
> of efficient processing on resources by applications that *just* want 
> to process URIs.  Opaque URIs would eliminate that increasing 
> possibility.
>  
> There are better (ie. generalized, scalable, flexible) ways 
> to provide access to resource descriptions than embedding 
> such knowledge in the URIs that denote them.
> 
> C.f. http://sw.nokia.com/URIQA.html
> 
> Cheers,
> 
> Patrick
> 
> 
> --
> Patrick Stickler
> Nokia, Finland
> patrick.stickler@nokia.com
>   
> 
> Best wishes,
> 
> - Mike
> ---------------------------------------------------
> Michael C. Daconta
> Chief Scientist, APG, McDonald Bradley, Inc.
> www.daconta.net 
> 
Received on Friday, 11 July 2003 12:19:44 GMT

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