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

RE: Digest URI's

From: McBride, Brian <bwm@hplb.hpl.hp.com>
Date: Fri, 7 Apr 2000 10:55:51 +0100
Message-ID: <7686E88F1253D311A867006008CD059F11373A@0-mail-1.hpl.hp.com>
To: "'www-rdf-interest@w3.org'" <www-rdf-interest@w3.org>
Dan and Sergey,

Thanks for the prompt responses. I think the heart of my difficulty is that
I don't understand the role of anonymous resources. Let me replay my
understanding of the answers to expose the bits I don't yet get:

1) What entitities can have digest URI's

	a) models
	b) statements
	c) otherwise anonymous resources 

Sergey wrote:

>On the syntactic level, digests can be used to give explicit URIs to
>"unnamed" resources used in some serialization syntax

My reading of the spec is that anonymous resources appear in the model, not
just in the syntax [m&s fig2, fig7]. Yes?  No?  This is the heart of my
problem.

2) What are they for?
	Model URI's give us a digest to sign a model's content.

	[A digest algorithm would be sufficient for this - doesn't have to
be a URI - Yes/NO?  What advantage does making it a URI bring?]

	Statement digests improve interoperability?

	[I don't get this one yet. How?  But they are needed to be able to
compute the model digest - and a standard way to do that seems like a good
thing.]

	Unnamed resources can be referred to.

	[I don't get that either.  The algorithm for referring to unnamed
resources depends on a particular seriliazation.  If I've plonked an
anonymous resource directly into a model in a database how do I compute its
digest?

	Does this have knock on effect?  The digests for statements
referring to the unknown resource depends on the digest for that resource,
and the digest for the model depends on the digests for those statements.

	So maybe the idea is:  If a resource is added into a model by a
program, then it is required to give it a URI - a guid or whatever.  But
since people are not very good at generating guid's, when a human writes
some RDF serialization which includes an anonymous resource, then the parser
has a standard algorithm for calculating a URI for that resource.  If that
is the case, then is this really a suggestion to remove anonymous resources
from the RDF model?]

	3) What does a digest URI denote

	What I was getting at here was the difference between variables and
values. Digest URI's denote values, i.e. <Temperature, San Francisco, 10>,
not "the current temperature in San Francisco" which is a variable.  Obvious
I guess, I was just trying to be careful. 

Brian McBride
HPLabs
Received on Friday, 7 April 2000 05:55:56 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Monday, 7 December 2009 10:51:43 GMT