I’m afraid we will just have to agree to disagree. To me, your claims are simply outlandish. You try to discuss URIs detached from their purpose of building interoperable information systems and their definition in the relevant internet and web standards. I see absolutely no value in doing that.

I think Richard is right when he says, with respect to recipe 3 in the best practice recipes document, “… I think that the 303 redirect in the RDF case is unnecessary, but doesn’t hurt either, and is probably not such a bad idea because of the symmetry between the HTML and RDF responses.”

In fact, perhaps the main reason why we chose to include a 303 redirect in the RDF case also is so that anyone retrieving the RDF data can maintain provenance information about the source of the data, and differentiate between different snapshots or versions of the data. I.e. if every time you (as the namespace owner) change the data you also change the redirect location, then you provide the basic framework for Semantic Web applications to talk about which version of an ontology they are committing to.

Your first objection to my argument is that the URL http://www.w3.org/Icons/valid-xhtml10 does not make a claim. And you show how someone may just mention it, in your example, by commenting on the quality of the design of the image that it returns. But any identifier, word, phrase, sentence, etc. can be mentioned, and in that context, it doesn’t have the effect that it would in an ordinary context. For example, I could say, “The URL to this post of yours has 70 characters in it” And in that context, it is a character string and doesn’t identify your post. Does that mean in ordinary use it does not identify your post? Of course not. Nor does your mention of the poor design of the badge that is returned when you access the xhtml-valid URL change its referent in ordinary use. Any URL can be mentioned. That doesn’t render it useless.

Your third objection is that the URI identifies “*just an image*”, not a claim. Why then is it named http://www.w3.org/Icons/valid-xhtml10? The URI minted by the W3C is named “valid-xhtml10″ for a reason. If it was just an image, they might as well have named it “image-123″. They named it “valid-xhtml10″ because they intended for it to be used to make a specific claim, namely that the page on which it appears uses xhtml that validates. Secondly, a machine can use (interpret, understand) the URI, “http://www.w3.org/Icons/valid-xhtml10″. It can be programmed conditionally based on finding that URI embedded in a page. For example, it may try to parse it as XML rather than use some lower level screen scrapping technique. The image is not the meaning of the URI, neither to a human nor to a machine. That URL’s proper interpretation is spelled out quite clearly by the creators of the URI in their help document I quoted, “To show readers that one has taken some care to create an interoperable Web page, a “W3C valid” badge may be displayed (here, the “valid XHTML 1.0″ badge) on any page that validates.” The image is for easy recognition by a human being, it is the URI that matters.

I think your second objection is the most interesting. Recall that it is your statement above, “A URI should be context-free and should identify the same thing wether it’Â’s in an RDF file or a database or an email message.” that I am arguing with to begin with. Now in your comment you say, “Second, even if it was a claim, then the meaning is not in the URI alone, but arises from the *act of embedding* (in RDF speak, from making a statement ‘:page123 :embeds :w3c_badge’). Of course, the meaning of any statement depends on the subject. This doesn’t make the property-value pair ambiguous.” In other words, first you say “A URI should be context-free…” and then you say, “…the meaning is not in the URI alone…” which two statements seem contradictory. Is is exactly my point that the meaning of the URI depends on the subject with which it is used, and so it is not context-free. You cannot interpret the referent of the URI without knowing the context of its use. You cannot determine which author claims which page is valid unless you know the context in which that URI was embedded. Without that context, it doesn’t refer to or identify anything.

Leo, I agree, when there’s only an RDF representation, then there’s no need for a 303. That’s the first scenario above. The need for a 303 arises only if we indeed want content negotiation and HTML on the foo URI.