RE: [xri] Bracketing Refs [Authority Resolution]

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

This email is to quickly illustrate the conclusion that came out of the very
end of Friday's XRI TC telecon where the editors discussed Steve's "ref
bracketing" proposal. The conclusion was that rather than introduce a new
element, we could just nest XRDS elements since the whole purpose of XRDS
elements is to contain XRDs.

We also agreed to add an attribute to XRDS -- xrds:XRDS/@xrds:ref -- of type
AnyURI that makes it easy to specify the absolute XRI being described by the
XRDS document.

Following here's an updated example. You can look at the xrds:XRDS/@xrds:ref
attribute to see the XRIs being described by each XRDS document -- it makes
it trivial to follow the refs.

In this example the original XRI being resolved is "xri://@a*b*c" and there
is only one Ref being followed -- "xri://@a*b" is a ref to "xri://@x*y"


<XRDS xmlns:xrds="xri://$xrds" xrds:ref="xri://@a*b*c">
	<xrd:XRD xmlns:xrd="xri://$xrd*($v*2.0)">
		<xrd:Query>*a</xrd:Query>
		...
		<xrd:Service>
			<xrd:Type>xri://$res*auth*($v*2.0)</xrd:Type>
			<xrd:URI>http://xri.example-a.com/</xrd:URI>
		</xrd:Service>
	</xrd:XRD>
	<xrd:XRD>
		<xrd:Query>*b</xrd:Query>
		...
		<xrd:Ref>xri://@x*y</xrd:Ref>
	</xrd:XRD>
	<XRDS xrds:ref="xri://@x*y">
		<xrd:XRD>
			<xrd:Query>*x</xrd:Query>
			...
			<xrd:Service>
	
<xrd:Type>xri://$res*auth*($v*2.0)</xrd:Type>
				<xrd:URI>http://xri.example-x.com/</xrd:URI>
			</xrd:Service>
		</xrd:XRD>
		<xrd:XRD>
			<xrd:Query>*y</xrd:Query>
			...
			<xrd:Service>
	
<xrd:Type>xri://$res*auth*($v*2.0)</xrd:Type>
				<xrd:URI>http://xri.example-y.com/</xrd:URI>
			</xrd:Service>
		</xrd:XRD>
	</XRDS>
	<xrd:XRD>
		<xrd:Query>*c</xrd:Query>
		...
		<xrd:Service>
		...service endpoints for "xri://a*b*c" here...
		</xrd:Service>
	</xrd:XRD>
</XRDS>

Also, this proposal has (we believe) zero impact on either trusted res or
caching. Each XRD element is still atomic, and is signed individually.

We are incorporating this into XRI Resolution 2.0 Working Draft 10 Editor's
Draft 04 today and plan to have it posted later today.

=Drummond 

-----Original Message-----
From: Steven Churchill [mailto:steven.churchill@xdi.org] 
Sent: Thursday, January 12, 2006 11:44 PM
To: xri@lists.oasis-open.org
Subject: [xri] Bracketing Refs [Authority Resolution]



This proposes a bracketing scheme for outputting Refs during the authority
resolution phase. This provides a human and machine readable way to
negotiate a nested Ref resolution hierarchy.

<XRDS>
    
    <XRD-A /> 
    <RefRes>
        <XRD-E />
	  <RefRes>
            <XRD-H />
    	  </RefRes>
        <XRD-F />
        <XRD-G />
    </RefRes>
    <XRD-B />    
    <XRD-C />
    <RefRes>
        <XRD-I />
    </RefRes>
    <XRD-D />

</XRDS>


The <RefRes> element is used to bracket the XRDs necessary to resolve a Ref.
The <RefRes> element MUST appear between two <XRD> elements. (It would never
fall at the beginning or end, and two <RefRes> elements would never appear
together.)

The final <XRD> in the <RefRes> is that used for the subsegment resolution
of the <XRD> that follows the <RefRes>. Therefore, in the example above, the
subsegment resolution XRD chain is:

    G, B, I, D

Note that, since the <RefRes> "replaces" the preceding <XRD> from a
subsegment resolution standpoint, the number of (top-level) XRDs in the
<XRDS> is always equal to the number of authority subsegments.

~ Steve




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