W3C home > Mailing lists > Public > www-rdf-interest@w3.org > March 2000

Re: Subclass of Thing/Resource

From: Tim Berners-Lee <timbl@w3.org>
Date: Sat, 4 Mar 2000 11:14:33 -0500
Message-ID: <030401bf85f4$bab546e0$a60a1712@col.w3.org>
To: <guha@epinions-inc.com>
Cc: "Guha" <guha@epinions-inc.com>, "www-rdf-interest" <www-rdf-interest@w3.org>

-----Original Message-----
From: Guha <guha@epinions-inc.com>
To: Tim Berners-Lee <timbl@w3.org>
Cc: Guha <guha@epinions-inc.com>; www-rdf-interest <www-rdf-interest@w3.org>
Date: Friday, March 03, 2000 5:37 PM
Subject: Re: Subclass of Thing/Resource

> I think many of these questions center around
>precisely defining what an RDF Resource Identifier
>is supposed to be.

I thought that you could always identify and RDF Resource
by referring to that described by a given bit of XML.

>   I agree that we need to distinguish between RDF
>Resource identifiers and URIs.

That isn't what I said.  I would say that one can in universal
formal system put no constraints on Thing.

I don't think RDF Resources have idenifiers.
The way the Web works is, that

- RDF statements may refer to URIs
- URIs may ridentify documents
- documents may parse to RDF models
- RDF models are sets oif rDF statements

RDF identification using URIs wrks like this:

- RDF statemnts may refer to URIs with fragment IDs
- URIs with fragemnt idenifiers may refer to bits of XML
- Bits of XML may contain RDF descriptions of a given Thing.

On the web,  URIs are a primary way of identifying things. But you can of
use any unambiguous property fo something to identify it.

>A URI is a pretty formal object
>(protocol + host + opaque string) whose definition pretty
>concretely  constrains what can have a URI.

No, the HTTP spec defined a relationship between an abstract Document and an
The SMTP spec defined the relationship between an sbtract Mailbox and an
You could

> By
>this definition, people, places, etc. cannot have URIs.

We could extend URIs to these thinsg


but that ain't the point.  It is introducing all this as basic
Now we have RDF we can identify someone indirectly. Suppose foo.rdf incldues

<rdf:description id="guha">
   <rdf:type resource="http://....dublicore#Person"/>
   <play:mailbox resource="mailto:guha@epoinions.com"/>

Now we can refer to your good self indirectly in two powerful ways. This
fragment effectively idenified you as that person who ahs mailbox
guha@epoinions.com.   Anyone else can now refer to you as that Thing which
is described by  foo.rdf#guha

This works just fine, and it is what the reference to the person type for
example means.  What I am saying is that while this works fine, I do also
need to refer to that element of XML. So we need a syntax to select which I
am talking about

<play:author  about1="#guha" resource="#tim">
<play:friend   about2="#guha" resource="#tim">

..meaning that I wrote the XML but I am a friend of the person.

This is exactly the parseType distinction in fact for embedded information.
I think there is an assymetry that the parseType allows you distinguish a
reference to XML from a reference to RDF for inline stuff but we need it to
linked stuff too. ..... (6)  (Issue for M&S)

> On the other hand, it would be very convenient to have
>a unique canonical identifier for refering to the one TimBL
>or one RalphSwick. In my reading, this is what the RDF
>Resource ID is. Everything (including literals, URIs, ...) could
>potentially have one of these.

Or many.  Something doesn't have to be unique to be unamiguous

>  I do think it would be nice if an application can assume
>some kind of structure to these identifiers, but not being
>able to do so would not be fatal.
> I agree with you that http://foo.org/bar.rdf#xyz is a lousy
>identifier for an object. To me, it just represents a position
>is a file.
> In the long run, the object identifier namespace will have
>to be like the DNS namespace.
> Reactions?
> guha
Received on Saturday, 4 March 2000 11:14:37 UTC

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