Re: RDDL and XML Schemas Proposed Recommendation

[Justin Couch <justin@vlc.com.au>]

Jonathan Borden wrote:

> This gets me thinking about RDDLs interactions with URI persistance
> policies - it would be good if in some way we can say:
> 
> xxx URI is equivalent to yyy URI
> ... so when you ask for something with xxx nature, treat something with yyy
> nature as equivalent.

This exists - the II URI resolver request. Is this URI equal/equivalent
to this other URI I've given you. Allows you to map URLs to URNs to
check equivalency.
 
> xxx URI is a subset of yyy URI
> ... so when you as for something with yyy nature accept something with xxx
> nature

You sorta get this with URIs. I can ask a URI to be resolved to a URL,
List of URLs or URN or List of URNs. Sometimes the resolver supports the
feature, sometimes it doesn't.  Basically, the RFCs allow you to permute
any URI to any other URI if there are equivalents. Once you have this
information, you can then trawl through the returned list and see if you
have something equivalent there. 

Subsetting is an interesting problem, and one that does not really map
well to URI concepts. A URI identifies a resource. How do you subset an
identifier when you really don't know what that identifier means until
the point you resolve it to a real resource instance. A subset only has
meaning after you map it to a fixed thing. Two different machines may
well map an identical URI to two completely different resources (eg an
ISBN) ending up with two different meanings of what that subset is.
 
-- 
Justin Couch                                    Author, Java Hacker
http://www.vlc.com.au/~justin/               Java 3D FAQ Maintainer
http://www.j3d.org/              J3D.org The Java 3D Community Site
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