RE: QA Tips: Make readable URIs

Le mer 18/08/2004 à 11:03, Victor Engmark a écrit :
> Take the URL http://www.w3.org/QA/2004/08/readable-uri: It tells me that
> the protocol is HTTP,

True; the URI scheme is indeed not opaque in a URI.

>  that it is a web page

Not true; the URI may not have been dereferenceable, and even being so,
it may be something else than what you would call a Web page; it could
be a picture, a sound file, a CSS style sheet, a piece of RDF, etc.

>  (for somebody not familiar
> with the web, w3.org might not look like the same), that W3 is an
> organization,

Not true either; although in HTTP URLs, the hostname part is indeed not
opaque - it asserts something about the server from which you may
dereference the said URI -, you should not read anything below that
level; the .org Top Level Domain has many non-organizations domain
names, and the associated name may mean something very different from
what you think; look at w3c.com for instance.

>  and that the readable-uri page was published by the QA
> group in August 2004.

Not true either; take http://www.w3.org/QA/2005/01/News2004 : I have
good reasons to believe it was not published in January 2005.

To summarize, when the Tips says that URIs are opaque, it doesn't mean
one should make sure her URIs are opaque to the rest of the world; it
simply reminds that somebody should not try to any semantics into a URI;
there are indeed a few parts one could read into (the URI scheme, in
some schemes, the authoritative part, ...), but generally speaking, no
one can assert that http://example.com/APictureOfARedElephant is a
picture of a red elephant or the 9th Symphony of Bethoveen until she
dereferences it.

> AFAIK, URLs are a subset of URIs, with the differences that:
> - a URL is not necessarily an identifier, while a URI is, and

A URL is an identifier; logically speaking, if you say that URLs are a
subset of URIs, you can't say that URIs have properties that URLs don't.

> - a URL points to data about something, while a URI doesn't have to
> point to the information.

The pointers that Olivier gave explains why this distinction is not
relevant.

> > [1] http://www.w3.org/TR/uri-clarification/
> > [2] http://www.w3.org/DesignIssues/Axioms.html#opaque

> This seems to me to indicate that URLs like abc://def.ghi.jkl/12345 are
> preferable to http://www.w3.org/QA/2004/08/readable-uri.

Nope; again, the tip doesn't suggest that one should make her URIs
opaque, but that one should not try to interpret someone else URIs.

> I always thought of it as more of a warning sign: Do not put more
> information into URIs than strictly necessary, and leave out all
> technical details.

Nope, that's a different (although as important) topic.

Dom
-- 
Dominique Hazaël-Massieux - http://www.w3.org/People/Dom/
W3C/ERCIM
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