Resolution Errors inside Descriptors

["Wachob, Gabe" <gwachob@visa.com>]

I have a use case where I would like to know that a resolution failed
and have that result expressed inside of  an XRI Descriptor.

Take the case where I am using lookahead (or proxied) trusted
resolution. If I request resolution of a subsegment that is not a
subsegment the responding authority is directly responsible for, how
does the proxy/lookahead resolver let me know as a client that there is
such a failure? If I'm resolving directly to an authority, I get a 404 -
but if I'm getting the result *indirectly*, we haven't said how such a
negative result is expressed or cached.

So I therefore think we need to have a mechanism for expressing a
negative result that can be cached and signed. Just an element inside a
XRI Descriptor - something like "Failure" or "Error" which contains a
code (a URI) and a textual description (which we don't specify - as in
HTTP). Now, there are a lot of concerns about extensibility and the
ability of a processor to only partially undersatnd an error condition
(such as HTTP's use of 3-digit error codes, or SOAP's use of
hierarchical error codes - from most general to more specific) - this
allows expression of as specific an error code as one wishes, without
loss of appropriate behavior by processing nodes that don't understand
themore specific error, but understand something more general. 

I'm not sure what mechanism we should use. I really don't want to invent
a bunch of error codes, or a complicated error extension mechanism, so
the simplest thing we could do would be best. Do we need to go beyond
something like:

<Failure>
   <Code>..some uri..</Code>
   <Description>...english language description...</Description>
   ... extension elements ... 
</Failure>
?

	-Gabe
 
__________________________________________________ 
gwachob@visa.com
Chief Systems Architect
Technology Strategies and Standards
Visa International 
Phone: +1.650.432.3696   Fax: +1.650.554.6817