W3C home > Mailing lists > Public > semantic-web@w3.org > September 2007

Re: What if an URI also is a URL

From: Richard Cyganiak <richard@cyganiak.de>
Date: Wed, 12 Sep 2007 23:13:23 +0200
Message-Id: <0178BEF0-B0B3-41E9-8C73-2197EE383237@cyganiak.de>
Cc: semantic-web@w3.org
To: "Edward Bryant" <edward.bryant@gmail.com>


On 12 Sep 2007, at 22:50, Edward Bryant wrote:
> I would think that the URL http://www.example.com/ without more  
> should never be used to refer to a specific page of a site, simply  
> because its not specific enough and that a reference to a specific  
> page as an information resource should not depend on which specific  
> page a server responds to the base URL with ( e.g., index.html,  
> index.php, index.php5, etc.)

Assuming we are talking about a usual web site, http:// 
www.example.com/ is one specific page: the homepage. Why should it be  
different? After all, if you open the URI in a browser, you get back  
a representation of a specific page.

It doesn't matter what the web server does internally in order to  
serve up a representation, so the question if it reads from  
index.html or executes index.php or does some evil mod_rewrite magic  
is just an implementation detail, it doesn't change what http:// 
www.example.com/ refers to.

To learn what a URI refers to, don't look under the hood of the  
server. Look at the representations returned via HTTP.


> I just started learning this myself, so someone please correct me  
> if I am off base here.
> Ed
> On 8/30/07, Oskar Welzl <lists@welzl.info> wrote:
> Am Donnerstag, den 30.08.2007, 22:28 +0200 schrieb Reto Bachmann-Gmür:
> > But talking about standards, why is this discussion on a list  
> which has
> > been replaced by semantic-web@w3.org?
> dumb boy hit [reply] again; changed it now.
> Maybe we'll have to change to topic, too, soon: This is going to be  
> somewhat
> like "What's the content of an information resource"?
> Am Donnerstag, den 30.08.2007, 22:30 +0200 schrieb Reto Bachmann-Gmür:
> > Oskar Welzl wrote:
> > > Pity, though, that there hardly seems to be an agreement on how to
> > > handle this issue, so simply by choosing the above URI myself I  
> will not
> > > prevent *others* making statements like
> > > <#thismail> mail:sender < http://oskar.twoday.net>
> > > when they refer to an update-notification they received from  
> the weblog.
> > >
> > Reading this I think I misunderstood what you mean with "blog" I was
> > referring to a blog as a changing collection of articles not as
> > something that sends email. If we agree that an information resource
> > can't be the mail:sender of a mail then the statement
> >
> > <#thismail> mail:sender <http://oskar.twoday.net>
> >
> > is necessarily wrong, as a GET request to http://oskar.twoday.net is
> > responded with a 2XX response and with this response the resource in
> > unambiguously an information[1]. resource.
> Well, the "sending mail"-example was certainly the outer limit of
> nonsense I could possibly construct to get the message through, but I
> meanwhile think my confusion has a different cause (and it was you who
> pointed me to it):
> Lets forget for a minute that a blog is more than just a collection of
> posts and usually has properties like "allowsCommentsFrom",
> "offersFeedType", "Blogroll" etc.
> Assume that it *is* a mere collection of posts, sorted by date, latest
> first, 10 per page. Period. You type http://my.blog.tld in your  
> browser
> to go there, subsequent pages can be reached with
> http://my.blog.tld/?start=11 etc.
> In one of your previous posts you wrote:
> "A Blog is an Information Resource which could be described as
> an ordered collection of posts, the HTML returned by the webserver is
> (or should be) a suitable representation of that thing."
> I didn't like this idea first (and said so, IIRC ;) ...), but it seems
> logical to me now. *If* we think of a collection of posts and nothing
> else, it would probably fit the concept of an "Information resource".
> And what URI other than http://my.blog.tld would we have to name it?
> On the other hand, the very content of the 10-posts-list returned  
> by the
> server (as what could be seen as the HTML-representation of the
> information resource "blog") is an information resource in its own
> right. Its "The 10 latest posts from my blog". No other way to  
> refer to
> it than via http://my.blog.tld again. Even in this simple construct, I
> can make statements about http://my.blog.tld  in one RDF-document that
> contradict each other, like (in OTN, oskars triple notation):
> http://my.blog.tld  dc:coverage a period from 2003-2007
> (this was about the blog)
> http://my.blog.tld  dc:coverage a period from Juli-August 2007
> (this is about the 1st page of the blog)
> Same for statements about who commented there etc. - many can be true
> for only one of the two information resources that are addressed by
> http://my.blog.tld
> To get around this, my original assumption was that before using a URI
> to name something, I should check if its suitable by narrowing the
> "information resource" as much as possible: take the representation  
> you
> get, take all possible interpretations of what it represents (a blog,
> the first 10 postings, the author himself) and always take the
> narrowest. What you end up with is, almost always, only a little more
> than "the document". I like this approach for its simplicity, but it
> breaks a lot. Take SIOC as an example. sioc:forum/sioc:site is exactly
> what we're talking about here; they always refer to it via a URI that
> is, in fact, "the first page of the collection". This is not wrong as
> such, it just creates ambiguity, which UIRs should not have.
> (In fact it was my current work on a SIOC-export that confronted my  
> with
> this boring question again after so many years.)
> Now I go the steep way and say that http://my.blog.tld, the blog,  
> should
> not be confused with http://my.blog.tld, the most recent posts. The  
> blog
> should have its own URI, as "10 most recent posts" is the narrower
> construct. Next question:
> I plan to use http://my.blog.tld/ID/names#thisblog as sioc:site and  
> have
> an RDF/XML-document at ../ID/names to further define #thisblog. Now  
> how
> do I point to the preferred link/bookmark/"entry point" (which is, of
> course, http://my.blog.tld/) with a well-known vocabulary? I was  
> tempted
> to use rss:link, but am very unsure about it... (Not finding a usable
> hint on Google made me even more uneasy with the whole topic, as this
> suggests nobody on this planet ever thought of *not* using the URI of
> the main page as the URI for the whole site.)
> So you see, even though there might have been a misunderstanding about
> the concept of a "blog", this wasn't the cause of my problems. Even  
> when
> following your 'collection of posts'='information resource'  
> definition,
> I get deeper and deeper into trouble.
> You already got me on a better track once by pointing out the somewhat
> vague definition of information resource - maybe you got some new  
> input
> for me to chew on ;)
> Thanks,
> Oskar
Received on Wednesday, 12 September 2007 21:13:48 UTC

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