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Re: URI Fragments

From: joel sachs <jsachs@csee.umbc.edu>
Date: Fri, 12 Mar 2010 10:38:55 -0500 (EST)
To: Nathan <nathan@webr3.org>
cc: Linked Data community <public-lod@w3.org>
Message-ID: <Pine.GSO.4.64.1003121008280.25226@sunserver1.cs.umbc.edu>
Nathan,

I'm not sure it's correct to refer to your examples as "primary" and 
"secondary" resources. As you point out, it is not true that

> if I remove http://www.w3.org/People/Berners-Lee/card then
> http://www.w3.org/People/Berners-Lee/card#i no longer exists.

since the first URI refers to an information resource, while the second 
refers to a non-information resource.

You seem to take this as an argument against fragment identifiers, but it 
doesn't just apply to hash URIs. If the server www.w3.org goes down, then 
all URIs that it dereferences become non-dereferenceable, whether they are 
hash URIs or slash URIs.

Now, must we stop using a URI when the server that dereferences it goes 
down? I think there are cases where the answer is no, where it makes sense 
to continue using the URI as an identifier, even if the URI is no longer 
valid as an address. In the above case, there are
many webpages making assertions about 
http://www.w3.org/People/Berners-Lee/card#i ,
and those assertions are valid, regardless of the existence of
the server www.w3.org. Making thoses assertions easy to find might be a
challenge, of course, which is why I would like to see rdf browsers do 
more than simply issue a GET on a URI when trying to resolve it.

Joel.


On Fri, 12 Mar 2010, Nathan wrote:

> Hi Again :)
>
> Last question(s) related to fragments.. if I have:
>  http://example.org/something
>  http://example.org/something#a
>
> Those are two unique URIs and thus two unique resources (?)
>
> And the semantics of a fragment means that
> http://example.org/something#a is a secondary resource, where
> http://example.org/something is the primary resource (?)
>
> Then if I delete a Primary resource, the secondary resources must also
> be deleted, true / false (?).
>
> Here are some examples, which may seem like over kill but some are
> interesting and generally I *feel* rules like this should be either
> always true, or always false, never varying.
>
> examples:
> if I remove a database table, then all it's rows also no longer exist.
> if I remove London then the Tower of London also no longer exists.
> if somebody removes me, then my arms also no longer exist.
> if I remove test.html then test.html#whatever no longer exists.
> if I remove test.rdf then test.rdf#this no longer exists
> if I remove http://www.w3.org/People/Berners-Lee/card then
> http://www.w3.org/People/Berners-Lee/card#i no longer exists.
>
> conversely:
> if I remove a row, the table still exists
> if I remove the Tower of London, London still exists
> if you remove my arms, I still exists and I'll find another way to type.
> if I remove test.html#whatever test.html still exists
> if I remove test.rdf#this, test.rdf still exists
> if I remove http://www.w3.org/People/Berners-Lee/card#i then
> http://www.w3.org/People/Berners-Lee/card still exists.
>
> If the above is true (secondary resource must also be deleted on removal
> of primary resource), then I should never use a fragment Identifier to
> refer to a non-virtual object (i.e. "me" a Person) - because I can't be
> deleted by simply removing a resource. (?)
>
> Regards!
>
> Nathan
>
Received on Friday, 12 March 2010 15:39:27 UTC

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