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Re: #rdfms-difference-between-ID-and-about (every document is in the Web)

From: Graham Klyne <Graham.Klyne@Baltimore.com>
Date: Fri, 15 Jun 2001 17:15:13 +0100
Message-Id: <>
To: Dan Connolly <connolly@w3.org>
Cc: rdf core <w3c-rdfcore-wg@w3.org>
At 09:20 AM 6/15/01 -0500, Dan Connolly wrote:
> > The fact that something can have a URI (and anything can, right?) doesn't
> > mean that it's got one.
>Suppose I say that it does. There's no argument to
>refute me, is there? i.e. there's no reason not
>to adopt this as an axiom.

Let's call this something X.  At this stage, I discern 3 possibilities:
(a)  X has no URI
(b)  X has a URI, but I don't know what it is
(c)  X has a URI and I know what it is

For performing a computation (in our case, interpreting a relative URI), I 
see no practical distinction between (a) and (b).  So, yes, I can adopt 
this as an axiom, but the inference rules I use to decide possible 
computations may need to be adjusted as a result.  (Previously, I had 
assumed that if X had a URI I could find out what it was.)

> >  From a practical viewpoint, having a URI but not knowing what it is
> > doesn't seem to be significantly different from not having a URI.
>But this isn't an issue of practical viewpoints; it's
>an argument of architectural constraints -- or rather,
>lack of them. So the difference is significant.
>You trust that I have a birthday even though you don't
>know it, right? By the same token, it seems easy
>enough to accept that resources have URIs even though
>those URIs aren't always specified.

I generally regard "architecture" as a means to achieve a practical end.

> > Because (by my lights) a CC/PP profile may be some data that doesn't have a
> > URI.
>We disagree on that.

OK, so we probably need to frame this discussion in terms that we agree about.

> > >Just think of everything as "on the Web".
> >
> > I don't.  That sounds to me more like a religion, or act of faith, than a
> > state of affairs.
>Well, that's how architecture and mathematics work, no?

Not entirely, I think.  One adopts a viewpoint that yields a desired result.

>i.e. by the same token, nothing compells you to agree that
>2+2=4, nor that the DNS has a unique root.
>But it follows from generally accepted axioms,
>so you do agree, right?

I dispute "nothing compels":  life in the modern world would get pretty 
tough for me if I rejected the notion that 2+2=4.  And accepting a unique 
DNS root helps me access Internet services.

> > >  It's a matter
> > >of perspective. There aren't any constraints in the
> > >design of the Web that allow you to deduce a contradiction
> > >from saying "every document is on the Web".
> >
> > More important, I think, than the lack of a contradiction is a sense of
> > common understanding (which, also, is an act of faith...).
>Alas, it's true that a lot of folks think of the Web

I think it's quite reasonable to think of the Web as being more than just 
HTTP+HTML, without necessarily accepting that it's omnipresent.  It's 
pretty easy to accept the web as a whole range of things that happen on the 
Internet;  for me, it's something of a stretch to also include the weekly 
groceries or the plants in my garden.  Sure, you can do this, but I think 
that when a concept is allowed too much free reign it loses its potency.

I'd say it's useful to develop the idea that the Web can relate to non-Web 
things, rather than say that everything is "in the Web" without distinction.

>I agree that this common understanding is somewhat lacking
>and important to achieve; I plan to spend considerable
>effort developing it over the next few years.

Be careful what you wish for...

>But meanwhile, the 10 year history of the Web
>is evidence that this axiom is useful; can we agree that
>for the purposes of the RDF spec, every document is in the Web?

I'll accept that every document, every collection of data, *can* be 
assigned a URI, which I think is sufficient for the purposes of the current 
discussion.  In my response to Danbri on this topic I said:

Maybe we might say that a relative URI is meaningful only if there *is* a 
URI (per 5.1.1-5.1.4) relative to which it can be evaluated?

This phrasing could be tightened up somewhat.  You might also want to say 
something about how to interpret a relative URI in RDF if there is no known 
base URI.


Graham Klyne                    Baltimore Technologies
Strategic Research              Content Security Group
<Graham.Klyne@Baltimore.com>    <http://www.mimesweeper.com>
Received on Friday, 15 June 2001 12:36:16 EDT

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