Re: Do resources have representations?

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/ Benja Fallenstein <b.fallenstein@gmx.de> was heard to say:
| Are you saying that "denote a resource" is the *only* thing that a URI
| does?

Yes, I think that's right.

| Then how can it be that two URIs that denote the *same* resource can
| give me *different* representations when I put them into my browser?

I think that's just a generalization of the rule that the
representations associated with a URI vary over time (and according to
other criteria as well).

I can easily setup my web server so that for a particular URI you
*always* get a different representation. That doesn't change the
resource that the URI identifies (in this case, perhaps it's "random
number generator" or "milliseconds since epoc").

| I.e., every time I go to <http://example.org/1434> I see one
| particular page, and every time I go to <http://example.net/~foo/bar>
| I see another particular page, yet the two URIs identify the same
| resource.
|
| How do you explain this?

I don't feel any compelling need to, any more than I feel a need to
explain why a given URI might return HTML, XHTML, PDF, RDF, plain
ASCII, GIF, PNG, Microsoft Word, or other representations depending on
header settings independent of the URI.

I do observe, however, that the assertion that 
<http://example.org/1434> and <http://example.net/~foo/bar> identify the
same resource is not one that I would accept without proof.

You can claim that <http://example.org/1434> and
<http://norman.walsh.name/knows/who#norman-walsh> identify the same resource.
And you can claim that 

  <http://example.org/1434> :hasArms "3" .
  <http://example.org/1434> :hasHeads "2" .

but that doesn't make it true that I have three arms and two heads. :-)

In short: it appears that you want to associate a URI with a particular,
closed set of representations *independent of* the act of retrieving them.
You can't. Representations are ephemeral, they change without warning and
without changing the resource that the URI identifies.

                                        Be seeing you,
                                          norm

- -- 
Norman.Walsh@Sun.COM    | Never contend with a man who has nothing to
XML Standards Architect | lose.--Gracián
Web Tech. and Standards |
Sun Microsystems, Inc.  | 
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Received on Monday, 28 July 2003 11:02:47 UTC