W3C home > Mailing lists > Public > www-tag@w3.org > January 2003

RE: URI Opacity Principle (was: Re: use of fragments as names is irresponsible)

From: Dare Obasanjo <dareo@microsoft.com>
Date: Tue, 14 Jan 2003 19:49:31 -0800
Message-ID: <B885BEDCB3664E4AB1C72F1D85CB29F804B7C7F5@RED-MSG-10.redmond.corp.microsoft.com>
To: <noah_mendelsohn@us.ibm.com>, "Sandro Hawke" <sandro@w3.org>
Cc: "Roy T. Fielding" <fielding@apache.org>, <www-tag@w3.org>

Hopefully if the architecture document says anything in this direction
it will lean away from URI opacity. The opacity of URIs is a problem for
in XML application, specifically those that use XML namespaces. A number
of issues that come up in XML applications would be a lot easier to
solve (e.g. how does one version XML namespaces?) if namespace names
were structured and not just glorified UUIDs. 


-- 
PITHY WORDS OF WISDOM 
The ideal vacation cottage is one that visits twelve but sleeps two.


This posting is provided "AS IS" with no warranties, and confers no
rights. 

>  
>  
> -----Original Message-----
> From: noah_mendelsohn@us.ibm.com [mailto:noah_mendelsohn@us.ibm.com] 
> Sent: Tuesday, January 14, 2003 7:38 PM
> To: Sandro Hawke
> Cc: Roy T. Fielding; www-tag@w3.org
> 
> 
> Roy Fielding writes:
> 
> >> Somewhere along the line the W3C got hooked on the notion 
> that URIs 
> >> are opaque and hierarchy is meaningless.  That is bogus, 
> as evidenced 
> >> by every decent information site on the web today.
> 
> As I think I've suggested once or twice, the TAG would do the 
> community a service IMO if it would clarify the degree to 
> which URI's are indeed to be 
> viewed as opaque.   When may their substructure be either 
> inspected or 
> built up incrementally, and when are they to be treated as 
> "black boxes"?
> 
> Tim BL provides one exposition of the opacity principle at 
> [1].  In general, I find that many correspondents on this 
> list and others both oversimplify and confuse the issues, and 
> one can make the case that the principle has not in fact been 
> stated sufficiently clearly (or, per Roy's note, perhaps it 
> is at times a false goal).  Surely it is confusing to hear on 
> the one hand that URIs are opaque, while on the other RFC 
> 2396 [2] goes to some length to provide hierarchical 
> substructure as a special case.  There is surely a sense in which:
> 
>         uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6
> 
> is more inherently opaque (assuming the "-"s are truly just for
> readability) than:
> 
>         http://example.org/root/sub1/sub2/mydoc.html
> 
> If URI's were really intended to be opaque, why not make most 
> every URI a uuid?
> 
> My impression is that the server implementing an HTTP 
> resource should indeed have the ability to process based on 
> the substructure of the URI. 
> Surely it is appropriate for the server to map the HTTP 
> example above to file system sub-directories should it choose 
> to do so? (Though of course, that's not required or visible 
> from the outside.)  Is it OK for a client to help you build 
> up the URI incrementally, one piece at a time?  IE does. 
> Is it OK to build a query string in a URI from a form?  
> Pretty surely, and Tim says so.  Is it OK for a client 
> history list to gather all the URI's that seem to be from 
> example.org and group them?  Common practice suggests "yes".  
> Can proxies cache based on the substructure of the URI?  I 
> would think that's desirable (but don't try it with the uuid: 
> scheme).  Is it OK to start guessing MIME types of 
> representations from that .html at the end?  True believers 
> seem to say no (and I guess I'm one of them).  Is it OK to 
> assume that the .html URI above references a Web page as 
> opposed to some human being associated with a web page as 
> opposed to some human being who has nothing to do with a web 
> page?  Seems to be the fodder for lots of rambling on this 
> list.  When is it appropriate for a client or other agent to 
> inspect the scheme as a means of determining a retrieval 
> strategy?  I'm still somewhat confused as to what folks such 
> as Roy think on this one, since we often hear that HTTP: need 
> not identify resources to be retrieved with HTTP (or maybe 
> I've misunderstood).
> 
> Anyway, I don't claim to have the answers, but it's very much 
> the sort of question I would expect the architecture document 
> to help settle.  Just saying "URI's should be opaque" seems 
> too simplistic, and thus confusing. 
> I'm glad Roy's note has brought it up.  Thank you!
> 
> Noah
> 
> [1] http://www.w3.org/DesignIssues/Axioms.html#opaque
> [2] http://www.ietf.org/rfc/rfc2396.txt
> 
> ------------------------------------------------------------------
> Noah Mendelsohn                              Voice: 1-617-693-4036
> IBM Corporation                                Fax: 1-617-693-8676
> One Rogers Street
> Cambridge, MA 02142
> ------------------------------------------------------------------
> 
> 
> 
Received on Tuesday, 14 January 2003 22:50:05 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Thursday, 26 April 2012 12:47:15 GMT