Yadis Spec .9 Change Proposal: Section 7.3.1 clarify multiple XRD

Dick Hardt dick at sxip.com
Sat Feb 11 17:52:30 UTC 2006

If there is only one XRD, why do we have this XML document rather  
then just some <link rel ...> tags for initial discovery?

On 10-Feb-06, at 11:37 AM, Drummond Reed wrote:

> One factor that may mitigate this risk somewhat is that I see few  
> reasons in
> a YADIS context for the provider of an XRDS document to provide  
> more than
> one XRD element. The multi-XRD capability is intended for XRI client
> resolvers and proxy resolvers who need to provide the results of a
> resolution request for a delegated (multi-authority) XRI. While this
> multi-XRD capability may also have uses in other potential resource
> description or service discovery scenarios, in the typical YADIS  
> scenario
> the XRDS document will just be self-describing and thus not need to  
> contain
> more than one XRD element.
> =Drummond
> -----Original Message-----
> From: yadis-bounces at lists.danga.com [mailto:yadis- 
> bounces at lists.danga.com]
> On Behalf Of Larry Drebes
> Sent: Friday, February 10, 2006 8:47 AM
> To: yadis at lists.danga.com
> Subject: Re: Yadis Spec .9 Change Proposal: Section 7.3.1 clarify  
> multiple
> I hope you are wrong :).   I suspect that the early use of YADIS  
> will be
> based around several common libraries and not one-off implementations.
> This flaw is very easy to test for, and if broken, it should be  
> easy to fix.
> larry-
> Martin Atkins wrote:
>> Unfortunately, this is one of those things that relying parties are
>> going to get wrong. I guarantee it!
>> Previous experience shows that there are two kinds of "wrong" when it
>> comes to implementing specs:
>> * You got it wrong so it doesn't work at all.
>> * You got it wrong so it works most of the time except in some funny
>> corner-cases and all of the spec authors are now scowling at you.
>> This is the latter. Implementors are (by and large) lazy. They'll
>> implement the bare minimum to make it look like it works. Most YADIS
>> resource descriptors are going to have only one XRD segment.
>> Implementors will probably use XPath like /XRDS/XRD/Service which  
>> will,
>> of course, match the service elements in *all* XRD segments.
>> So while it's obvious the YADIS spec has to take a definite  
>> position on
>> this subject, everyone should be prepared for the fact that almost  
>> every
>> relying party implementation is going to get this wrong and consider
>> what the implications of this are.
>> Cheers,
>> -Martin

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