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Re: A parable about RFC 3986.

From: Pat Hayes <phayes@ihmc.us>
Date: Wed, 25 Jan 2012 11:17:24 -0800
Cc: public-awwsw@w3.org
Message-Id: <5D74FD75-CA51-4EC5-B9C3-031FE447A11B@ihmc.us>
To: Jonathan A Rees <rees@mumble.net>

On Jan 25, 2012, at 8:00 AM, 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.

Um. OK, but that usage of "representation" can't be the one used in Roy's thesis and the HTTP specs. 
>  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.)  Now A is a representation of the state of the
> referent of U, while B isn't; and vice versa for B.  Since the two
> referents have different properties / classes / theories, they can't
> be the same.  

Whoa. That does not follow. One thing - in the case where 'they' are the same - can satisfy two different descriptions without any contradiction arising. This happens all the time, eg consider current political debates in the USA. I think that the proper conclusion to draw here is that Alice and Bob have different notions of what constitutes a "state".

> 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).
> 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".  

I like that idea and even the name, although in my font it looks awfully like "FLAT resource"

> 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.  

I think that is pretty much what TimBL had in mind when he coined the 'information resource' terminology: a resource which can be *completely* described by its representations. No?

> 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.

Why not, then, *define* it to be the set of its states representations? And come to think of it, isnt that exactly what Roy did, when he *defined* a resource to be a function from times to representations? 

>  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.

Slightly too strong. You might know things about a set without knowing all its members. I know that the set of irrational numbers is uncountably infinite, but I dont claim to be intimate with every irrational number. 

> How this relates to the debate:
>  - Information resources (generic resources) are fiat resources, but
>    there could be fiat resources that are not information resources.

Example? And is it really worth making this distinction?

>  - 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.

Fiat ASPECT seems like a new idea. You need to elucidate this more. If I am non-fiat but have fiat aspects, does this mean there is another thing, a fiat-thing corresponding to me in some way? What way?

>  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).

True. But I dont see this as very different from the http-range-14 that we all know and love. 


> Jonathan

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Received on Wednesday, 25 January 2012 19:18:51 UTC

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