RE: [xri] Proposed XRD schema

["Drummond Reed" <drummond.reed@cordance.net>]

Will, great questions, see inline. (I expect the only reason Eran hasn't
beaten me to this is his workload this week.)

> -----Original Message-----
> From: Will Norris [mailto:will@willnorris.com]
> Sent: Tuesday, March 10, 2009 5:16 PM
> To: xri@lists.oasis-open.org
> Subject: Re: [xri] Proposed XRD schema
> 
> A few questions regarding the XRD schema, referencing http://wiki.oasis-
> open.org/xri/XrdOne/XrdSchema
> ...
> 
> What is the cardinality of XRD:Link:URI and XRD:Link:URITemplate?  I'm
> guessing 0 or more?

I think Eran just ran out of time when he first sent the proposal to the
list (I then transcribed what he sent to the wiki). But yes, I believe it's
0 or more.

> How is XRD:Link:URITemplate defined (or planned to be defined)? Is it
> along the lines of draft-gregorio-uritemplate or a more limited
> vocabulary akin to Link-Pattern defined in draft-hammer-discovery-02 ?

Eran can answer definitely but I believe the plan is to base it on
Link-Pattern.

> What would be the resource URI passed into the URITemplate?
> XRD:Subject? XRD:Link:LocalID? XRD:Link:Subject? Or is it application
> specific?

It would be the equivalent of the XRD:URI element, which is the URI of the
linked resource. There are no additional semantics, i.e., it URI MIGHT be
the Subject identifier for the linked resource, or it might only be an Alias
for it. Note that are planning on defining any anyURI child element of
XRD:Link with a cardinality of 0 or 1 that is the Subject identifier of the
linked resource.

I have expressed to Eran that I believe XRD:Link child elements should be
able to express the same set of identifier semantics about the linked
resource as XRD: child elements can express about the described resource.
However Eran does not want to use the same element names in both places
(i.e., he doesn't want the only different to be the containing context -- he
thinks that will be confusing to XRD users). So right now:

	XRD: Level			XRD:Link Level
	==========			==============
	XRD:Alias			XRD:URI or XRD:URITemplate
	XRD:Subject			TBD

Eran, do I have this all right?

> How do XRD:Link:URI and XRD:Link:URITemplate compare with regard to
> their priority attributes?  Is URITemplate really just a variation of
> URI or does it have a different semantic meaning?  Is it expected that
> an XRD parser/consumer will collapse URI and URITemplate elements when
> sorting them by priority?

My answer: they are treated identically semantically. In fact I think the
XML schema for XRD should specify that it's a Choice between one or the
other - you can't use both under the same XRD:Link. But that's something we
should discuss on tomorrow's TC call.

> If some of these things simply haven't been worked out yet, that's
> totally fine... it's just difficult to differentiate between actual
> discussion items and things which are stuck in someone's head and just
> haven't made it out onto the wiki
> yet.

No, you are in exactly the right place. The wiki page
(http://wiki.oasis-open.org/xri/XrdOne/XrdSchema) is where we have been
documenting this until Eran is able to get a first draft spec out, but we
haven't quite finished everything on that page yet. Let's make it a goal of
tomorrow's telecon to do that, and between us bring it up to date. Then we
won't be waiting on Eran so much (though we don't want to take any pressure
off him ;-)

=Drummond