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Subject: Re: [xri] Backtracking

Tan, William wrote:
> 1. Authority resolution and service selection are distinct phases.  
> When authority resolution completes, it is done and returns the  
> result to the calling function. It might be at the 3rd Ref out of 5  
> possible Refs, and there is no way to continue where it left off.
> 2. During service selection, if you see a Ref, you will spawn a  
> different authority resolution phase, but that has nothing to do  
> with the original authority resolution. This child authority  
> resolution phase also knows nothing about service selection. It  
> completes, and returns (if successful) the results back to the  
> caller, which is the service selection function. If this child  
> authority resolution phase fails and there are more Refs, the  
> service selection function will spawn another authority resolution  
> phase on the next Ref.

Yes, well said, and that matches my understanding.

John Bradley wrote:
> This is the tricky bit.  I am informed that the current spec sec  
> 11.5 intends that if the final XRD is returned and you do service  
> selection on it,  and if that "does not" find the required SEP then  
> you must unwind back to the same point that you would have if the  
> XRD was not returned.

So, are you saying that if I resolve @a*b*c and the XRD for *c does  
not contain the SEP I'm looking for, nor any REFs, I should go back  
and look in *b for that SEP? That would not make any sense to me.

If however I follow an XRD level REF that I found in *c, and do not  
find the SEP I'm looking for in the last XRD for -that- resolution  
chain, I can go and examine any other REFs that I might have found in  
*c. But once I start following REFs, I cannot backtrack to before the  
XRD where I started following REFs.


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