W3C home > Mailing lists > Public > www-tag@w3.org > July 2002

resource equivalence was: Re: fragment identifiers

From: Jonathan Borden <jonathan@openhealth.org>
Date: Wed, 24 Jul 2002 09:40:23 -0400
Message-ID: <056701c23317$aaea2050$0a2e249b@nemc.org>
To: "Roy T. Fielding" <fielding@apache.org>
Cc: <www-tag@w3.org>

Roy T. Fielding wrote:
> A URI is an identifier.  The semantics of the resource it identifies
> are defined by the sameness of representations of that resource over
> time, not by any property of the identification system used to create
> that identifier. In short, a URI reference has the semantics that
> other people assign to it when they persist in trying to use it to
> refer to something useful.

Terrific. This para should (IMHO) be included in the "arch doc".

BTW: I've suggested equating resources by the equality of their
representation sets as axioms [10,11] in

[10] equivalent(URIa,URIb) := Entities(URIa) = Entities(URIb) and
cardinality(Entities(URIa)) > 0

Two URIs are equivalent when they map to the same set of entities.

[11] equivalent(A,B) <=> exists URIa such that A = resource(URIa) and exists
URIb such that B = resource(URIb) and equivalent(URIa,URIb)

Two resources a and b are equivalent if the set of entities given the URIa
and URIb are equal where URIa identifies a and URIb identifies b.

where Entities(URI) is the set of entities which the URI maps to across
media-types, time, and other e.g. HTTP request parameters.

> This isn't a property of the technology;
> it is a property of how people use the technology.  The same is
> true of "words", whether or not you are prepared to admit it.
> That is the basis of every modern human language except French.

Just curious, what is the problem with French?

URIs _are_ words, words that may be attached to their dictionary (e.g.
"http:...", but nonetheless.

> Some identifiers are better (more persistent, more available, more
> whatever-you-like) than others.  http identifiers are ideal for
> resources that can be accessed through HTTP via TCP/IP.  Other
> identifiers may be better for some cases, but only if they come
> with a support infrastructure that makes them sufficiently useful
> for people.  People decide what identifier is best for any given
> situation, and it is a fundamental principle of the Web that
> any URI scheme can be used as an identifier within any context or
> protocol element that requires a URI.
> XML namespaces, by the way, can be accessed through HTTP, as can
> robots, climate controls, beaches, and any other thing for which
> someone cares to provide a meaningful representation via HTTP.

oh yeah.

Received on Wednesday, 24 July 2002 09:46:24 UTC

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