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Re: resource equivalence was: Re: fragment identifiers

From: Roy T. Fielding <fielding@apache.org>
Date: Thu, 25 Jul 2002 14:47:57 -0700
Cc: <www-tag@w3.org>
To: "Jonathan Borden" <jonathan@openhealth.org>
Message-Id: <2E484952-A018-11D6-8DB8-000393753936@apache.org>

> BTW: I've suggested equating resources by the equality of their
> representation sets as axioms [10,11] in
> http://www.openhealth.org/RDDL/SchemaAlgebra
>
> [[
> [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.

Not quite.  You have left time out of the equation, which is probably
the most frequent error made in reasoning about resources.  What makes
something a resource is that people can go back to it at a later time,
or an "earlier" time if version history is available, and obtain the
same semantic mapping even though the representation(s) may have changed.

In other words, two URI are equivalent if, for all time t,

    M(URIa, t) == M(URIb, t)

Naturally, that isn't a very useful function, which is why we need
additional assertions in order to establish the semantics of a
resource beyond "what can be observed."  I believe that is why RDF
exists.  RDF can assert that two URI are equivalent if the author
anticipates that they will map to an equivalent set of representations
over all time.

>> 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?

Last I checked, France had a special language bureaucracy that
determines what is or is not Franšaise.

....Roy
Received on Thursday, 25 July 2002 18:00:27 GMT

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