Re: RDF

I've been feeling that this is is the crunch point, and wonder
why I didn't like Mark's expression of REST, and looking for
the appropriate email of Roy's to respond to but I'll use this.


Here is the test case to distinguish between
Roy's model and mine - and find whether they really are different.

The only measurable property of an HTTP resource is
the set of representations one gets.
So let's take the test case of the car.

Roy says its fine for one to get a picture of the car one
day and from the next day get a video tape or an audio track,
because they are all "representations" of the car.
Now I don't know how that "being a represnetation of the car"
actually constrains them.

(Remember I use "representation" for the process of taking
a conceptual work and making bits of it, and Roy seems to use it
for the process of making a conceptual work which describes something,
and then making a digital tim:representation of that)

Well I'm perfectly happy with content negotiation over
different content types, to the extent that the different
representations can be considered to some extent
the same message in a different medium.

What are the bounds?

Suppose one representation is a copy of the invoice for the car, and 
another
is a copy of the repair manual?

Are they both roy:representations of the car and therefore is it 
reasonable
behavior for a server?

Suppose one representation is a legal document about the car,
and another representation was that legal document with "not"
inserted somewhere?

If you, Roy will accept that is bad practice -- and abuse of the system
not condoned by the specs, then we have a constraint that
all representations must be related in some way, besides simply
the subject.

Actually I think this is very important in practice. We can't have a web
where the content-negotiated versions differ in legal meaning.
It must be an error (and potentially fraudulent is done deliberately in 
order to
steal) to make content-negotiated representations of the same resource
inconsistent.    If REST philosophy allows it, then we need to
further constrain the web so that it works.
Basically, the power of a hypertext link, or any reference using URIs
is destroyed if you don't have the repeatability, that when you 
reference the URI
again you basically get the same  thing -- to within some expectations
shared by the quoter and the publisher.
Its very important for accessibility and internationalization, of 
course.

The actual extent to which different representations differ is
of course controlled (As Roy noted earlier) by the publisher, but that
doesn't mean that there is no social pressure and real need for 
publishers
to be reasonable.

So, if, Roy, you will accept that there is some such constraint
on the set of representations, then I can associate the
conceptual work in my model with that set of representations. Then we
just have a problem of nomenclature on our hands.  I think
we can make an architecture in which formally the thing identified
is the message, and in certain contexts would be used as
an indirect identifier to indicate the subject of the representations.

If you don't accept that there is such a duty of the publisher, then we
have a serious problem on the web.  Or rather, we would have if
the web really worked like that.  But rather, we would have failed to
capture in the architecture the constraints which actually make the web 
work.
Because, after all, people do operate with this constraint.
So we aren't imposing new rules.

Tim BL

On Monday, Jan 27, 2003, at 01:57 US/Eastern, Mark Baker wrote:
>
> - the concept of love is a "resource", an abstraction
> - resolving an identifier for the concept of love will end up as a GET
> request on some Web server/proxy (just to bridge with your "Web 
> location").
> - the resolution of that identifier will return documents that 
> represent
> the resource
>
> The REST model is the most appealing of the models I've seen presented,
> as it seems to be at least as powerful(*) as TimBL's, plus it's more
> general, since http: URIs would be able to identify anything; love,
> cars, people, etc..
>
> (*) the implementation would need work to match TimBL's model, ala an
> HTTP extension header called "ConceptualWork" whose value is a URI.
> But the model seems adequate, if only because this extension is
> possible.
>
> MB
> -- 
> Mark Baker.   Ottawa, Ontario, CANADA.        http://www.markbaker.ca
> Web architecture consulting, technical reports, evaluation & analysis

Received on Tuesday, 28 January 2003 22:44:26 UTC