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Re: Referencing items in RDF

From: Dan Brickley <danbri@w3.org>
Date: Sun, 3 Sep 2000 09:15:30 -0400 (EDT)
To: Aaron Swartz <aswartz@swartzfam.com>
cc: RDF Interest <www-rdf-interest@w3.org>
Message-ID: <Pine.LNX.4.21.0009030855410.29646-100000@tux.w3.org>
On Sun, 3 Sep 2000, Aaron Swartz wrote:

> Is there a way, or a URI format, to represent the value of an RDF statement.
> That is, given these two URIs:
> 
> http://www.w3.org/Home/Lassila
> http://xmlns.com/example/1.0/Creator
> 
> How do I represent the value "Ora Lassila"?

One way is like this: "Ora Lassila". The value represents itself quite
well.

Literal strings are something like un-named resources, you identify them
through providing their content, since they
don't themselves have Web names (URIs). Like other resources, you might
also identify them through description. Just as we might say "the company
whose homepage is xxx" or "the person whose personalMailbox if yyy", we
might say "the chunk of nameless data whose foo-checksum is zzz". This
kind of strategy can uniquely pick out something without using/needing a
URI for it.

If you're after a way of representing literal data within a URI,
that's been done (and to my suprise implemented in browsers). You're after
the data: URI scheme. This is a way of tunnelling blobs of mime-typed data
through URI syntax.

Netscape browser for example seems to understand this (try pasting into a
Web page somewhere).

<img src="data:image/gif;base64,R0lGODdhIAAgAIAAAAAAAPj8+CwAAAAAI
    AAgAAAClYyPqcu9AJyCjtIKc5w5xP14xgeO2tlY3nWcajmZZdeJcG
    Kxrmimms1KMTa1Wg8UROx4MNUq1HrycMjHT9b6xKxaFLM6VRKzI+p
    KS9XtXpcbdun6uWVxJXA8pNPkdkkxhxc21LZHFOgD2KMoQXa2KMWI
    JtnE2KizVUkYJVZZ1nczBxXlFopZBtoJ2diXGdNUymmJdFMAADs=" /> 


There's some support for this in the Perl URI module too (which was what I
found when I went Googling to find you a citatation)

http://theoryx5.uwinnipeg.ca/CPAN/data/URI/URI/data.html
see also:
http://lists.w3.org/Archives/Public/xml-uri/2000May/0269.html

here's the path to the rfc:

http://www.w3.org/Addressing/
http://www.w3.org/Addressing/schemes.html
http://www.w3.org/Addressing/schemes.html#data
ftp://ftp.isi.edu/in-notes/rfc2397.txt

	 The "data" URL scheme

	1. Abstract
	
	   A new URL scheme, "data", is defined. It allows inclusion of small
	   data items as "immediate" data, as if it had been included
	   externally.


Here's another one to play with:

data:image/gif;base64,R0lGODdhMAAwAPAAAAAAAP///ywAAAAAMAAwAAAC8IyPqcvt3wCcDkiLc7C0qwyGHhSWpjQu5yqmCYsapyuvUUlvONmOZtfzgFzByTB10QgxOR0TqBQejhRNzOfkVJ+5YiUqrXF5Y5lKh/DeuNcP5yLWGsEbtLiOSpa/TPg7JpJHxyendzWTBfX0cxOnKPjgBzi4diinWGdkF8kjdfnycQZXZeYGejmJlZeGl9i2icVqaNVailT6F5iJ90m6mvuTS4OK05M0vDk0Q4XUtwvKOzrcd3iq9uisF81M1OIcR7lEewwcLp7tuNNkM3uNna3F2JQFo97Vriy/Xl4/f1cf5VWzXyym7PHhhx4dbgYKAAA7


> **Has it been done?

sort of (see above)

> I assume that the benefits of having a URI to represent RDF values would be
> obvious -- URIs are extremely useful and are supposedly extensible to
> represent anything with identity.

Yes... the data-aggregating power of RDF largely comes from having
piggybacked on the Web naming system. That said, I think sometimes in RDF
land we've over emphasised the need to have URIs for
everything. Oftentimes we'll be able to get by through identifying
resources by description rather than by name (now we've got a framework
for describing resources!). It's a bootstrapping thing...

Not sure if this answers your question!

Dan
Received on Sunday, 3 September 2000 09:15:31 GMT

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