Re: A parable about RFC 3986.

Hi Jonathan,

I suspect that any attempt to distinguish "fiat resources" from
"non-fiat resources" will suffer the same fate as attempting to
distinguish "information resources" from "non-information resources".
But I want to try to follow and understand the scenario that you
present . . . .

On Wed, 2012-01-25 at 11:00 -0500, Jonathan A Rees wrote:
> Speaking loosely below, do not imagine I take this completely seriously...
> 
> Suppose there is a person P, and two fixed documents
> ("representations") A and B.  Alice says that A is a representation of
> the state of P and B isn't, while Bob says the opposite.  Alice mints
> a URI U "identifying" P and serves A as a retrieval result (200
> response to a GET request), while Bob mints a URI V also "identifying"
> P but serves B as a retrieval result.  (The HTTP spec says that an
> HTTP retrieval result gives a representation of the state of the
> identified resource.)  

Well, actually HTTPbis says that the representation *reflects* the state
of the resource, 
http://tools.ietf.org/html/draft-ietf-httpbis-p3-payload-18#section-4
but hopefully that detail is immaterial here.

I think it is important to analyze this scenario in terms of who has
asserted what.  In effect, Alice has asserted (via her server
configuration) that A is a representation of the resource identified by
U, and she has (presumably) also somehow declared that U identifies P.
Similarly Bob has asserted that B is a representation of the resource
identified by V, and he has (presumably) declared that V identifies P.  

> Now A is a representation of the state of the
> referent of U, while B isn't; and vice versa for B.  

I presume you mean that Alice has asserted something that contradicts
what Bob has asserted, but I don't understand exactly what those
assertions are or where they came from.  Can you clarify?  Does A
contain statements that are contradictory to statements in B?  Or are
you assuming a more indirect contradiction that relies on the generic
metadata inference rule:
http://www.w3.org/2001/tag/awwsw/ir/latest/#metadata
[[
(A1)     M[G] if and only if {M[S] for all S such that S instantiates
G}.
]]

> Since the two
> referents have different properties / classes / theories, they can't
> be the same.  

They can unless those properties are mutually contradictory, i.e.,
unless there are no satisfying interpretations when you assert:

  <U> owl:sameAs <V> .

> But this is a contradiction, since then A would be both
> a representation of the state of P, and not a representation of the
> state of P (and similarly for B).

I don't understand how the fact that A is a representation of <U> and B
is a representation of <V> come into play here.  Can you clarify?  Where
are these contradictory assertions made?

For simplicity, I will assume that A and B are served as RDF documents
with HTTP 200 responses, and A says something like:

  # Graph GA:
  <U> owl:sameAs <P> .
  <U> :color :RED .

and B says something like:

  # Graph GB:
  <V> owl:sameAs <P> .
  <V> :color :NOT_RED .

(where :RED and :NOT_RED are mutually exclusive).

As the URI owner of U, Alice has declared that <U> identifies a resource
that is <P> and is also :RED.  Similarly, Bob has declared that <V>
identifies a resources that is <P> and is also :NOT_RED.  Graph GA
probably has satisfying interpretations in isolation, and graph GB
probably also has satisfying interpretations in isolation.  But when GA
and GB are merged, the resulting graph has no satisfying
interpretations, because Alice and Bob have made contradictory
assertions about <P>.  

This just looks to me like a case of different people asserting
contradictory things.  I don't see why the nature of P needs to come
into play here, but I assume that is because I do not yet fully
understand your scenario.  If you could clarify what the conflicting
assertions are and where they came from, that would help.

Thanks,
David


> 
> What assumption might we want to discard in order to remove the
> contradiction?  I would suggest that the state of a person does not
> have representations.  Let's define a class of resources called "fiat
> resources".  What distinguishes a fiat resource is that the
> representations of its states are *constitutive* of the resource -
> they are not subject to debate, reason, opinion, and so on, but are
> rather part of the resource's identity.  So a person is not a fiat
> resource, since Alice and Bob can argue about whether A and B are
> representations of its states; while the referents of U and V are fiat
> resources, since Alice and Bob get to decide what their states'
> representations are.  [Unless the explicitly adbicate this privilege.]
> 
> A fiat resource bears the same relationship to its states'
> representations as a set bears to its members.  If you don't know what
> the members of a set are, you don't know what the set is.  If you
> don't know a fiat resource's representations, you don't know what fiat
> resource you're talking about.
> 
> How this relates to the debate:
> 
>   - Information resources (generic resources) are fiat resources, but
>     there could be fiat resources that are not information resources.
> 
>   - Fielding's REST resources come in two flavors, formal and
>     informal.  His formal definition (mapping from time to sets of
>     representations) is only the fiat aspect of the resource, not other
>     aspects of the resource.  Those other aspects are captured in the
>     informal discussion.  So a fiat resource could be considered to be
>     a pair of a Fielding-formal-REST-resource and a
>     Fielding-informal-REST-resource.
> 
> This suggests a position intermediate between a free-for-all where a
> retrieval-enabled hashless HTTP URI (REHHU) can refer to anything at
> all, and where it has to refer to an information resource: say that
> a REHHU has to refer to a fiat resource. We have proven the latter,
> while the more restrictive (and useful) information resource rule is
> wishful thinking.
> 
> I suspect that my "fiat resource" is much more similar to David's
> "information resource" than my "information resource" is, if for no
> other reason that David's "information resource" is so much like Roy's
> formal REST resource.
> 
> This idea doesn't help the cause of metadata (Tim's and my cause), but it
> at least explains the relationship between resources and HTTP in a way
> that is consistent with the specs and with Fielding's world view - and it says
> that the REHHU situation is not a free for all, it is constrained, so you can't
> name a person with a 200-yielding URI (since people aren't fiat resources).
> 
> Jonathan
> 
> 
> 

-- 
David Booth, Ph.D.
http://dbooth.org/

Opinions expressed herein are those of the author and do not necessarily
reflect those of his employer.

Received on Wednesday, 25 January 2012 17:47:22 UTC