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Subject: RE: [xri-editors] XRIs and canonical form


The argument against requiring canonical form for resolution is that it puts the canonicalization requirement on the client (instead of the server). 

So I guess I'm ok with some non-normative text, if you feel thats the best way. But I would at least suggest that by making it non-normative, we would have to mention in resolution that a local access server (and a naming authority server, perhaps) has to implement either canonicalization or equivalence rules locally (on the server side). Clients (resolvers) will *also* have to do this if they ever want to compare XRIs. 

	-Gabe

> -----Original Message-----
> From: Dave McAlpin [mailto:dave.mcalpin@epokinc.com]
> Sent: Tuesday, November 11, 2003 12:14 PM
> To: 'Wachob, Gabe'; xri-editors@lists.oasis-open.org
> Subject: RE: [xri-editors] XRIs and canonical form
> 
> 
> Right, I just want to make sure we're comfortable tackling 
> something that
> others have chosen not to define. HTTP 1.0 (RFC1945) provided a simple
> definition of canonical form but it was removed in 2068, 
> apparently after
> some thought and discussion. Massinter's comment below is an 
> argument not to
> reintroduce the concept in 2616.
> 
> 2396 avoided the issue entirely and 2396bis only provides general,
> non-normative guidance.
> 
> All those specs chose to focus on equivalence rules rather 
> than a canonical
> form, which is exactly what we've done up until now. I'm just 
> asking if
> we're really sure about this before I start working on it.
> 
> Dave
> 
> > -----Original Message-----
> > From: Wachob, Gabe [mailto:gwachob@visa.com]
> > Sent: Tuesday, November 11, 2003 11:32 AM
> > To: 'Dave McAlpin'; Wachob, Gabe; xri-editors@lists.oasis-open.org
> > Subject: RE: [xri-editors] XRIs and canonical form
> > 
> > While this is true (about canonicalization of cross 
> references), I think
> > its perfectly reasonable to talk about canonicalization of 
> those parts we
> > have control over (ie XRI-defined syntax).  Perhaps 
> "canonical" is too
> > strong a word.
> > 
> > I suspect that the vast majority of XRIs will not contains cross
> > references containing other URI schemes. And in those cases 
> where they do,
> > maybe we'll have to live with the fact that there is not 
> one canonical
> > form.
> > 
> > Maybe we call it "XRI canonicalized URI form" to suggest 
> that its only
> > canonicalized as far as XRI syntax goes..
> > 
> > 	-Gabe
> > 
> > 
> > > -----Original Message-----
> > > From: Dave McAlpin [mailto:dave.mcalpin@epokinc.com]
> > > Sent: Tuesday, November 11, 2003 11:06 AM
> > > To: 'Wachob, Gabe'; xri-editors@lists.oasis-open.org
> > > Subject: RE: [xri-editors] XRIs and canonical form
> > >
> > >
> > > It's interesting that neither 2396 nor 2616 defined a 
> canonical form.
> > > 2396bis defines some "good practices" for making URIs "reasonably
> > > canonical", but they don't attempt anything normative. The
> > > following post by
> > > Larry Masinter is instructive.
> > >
> > > > In general, URLs do _not_ have a canonical form. However, HTTP
> > > > defines some equivalences for URLs (e.g., that http://host is
> > > > equivalent to http://host/, and by using the generic
> > > > syntax for host names, the host part is case insensitive).
> > > >
> > > > Some particular HTTP servers MAY define other equivalences,
> > > > e.g., that http://host/dir is equivalent to http://host/dir/
> > > > and to http://host/dir/index.html.
> > > >
> > >
> > > Given that URIs don't have a normative canonical form, it's
> > > hard to see how
> > > we can define a canonical form for XRIs that contain 
> cross-references.
> > >
> > > Dave
> > >
> > > > -----Original Message-----
> > > > From: Wachob, Gabe [mailto:gwachob@visa.com]
> > > > Sent: Tuesday, November 11, 2003 10:58 AM
> > > > To: 'Dave McAlpin'; xri-editors@lists.oasis-open.org
> > > > Subject: RE: [xri-editors] XRIs and canonical form
> > > >
> > > > I think canonical form is sort an arbitrary, but well
> > > understood "state"
> > > > of an identifier.
> > > >
> > > > When an identifier is in canonical form, it should be
> > > possible to compare
> > > > it with another identifier in canonical form and the
> > > process of comparing
> > > > the two character-by-character (or in the case of
> > > canonicalized URIs, byte
> > > > for byte) is exactly the process of applying the built-in
> > > equivalence
> > > > rules in the XRI spec.
> > > >
> > > > Does this make sense? I mentioned the leading-. issue, the
> > > $! and ! cross
> > > > references. One other thing that would be useful to describe for
> > > > canonicalization is the uppercasing of %HH (hex digit)..
> > > >
> > > > If we define resolution to operate only on 
> canonicalized forms of
> > > > identifiers, it potentially makes the deployment of XRI 
> local access
> > > > servers MUCH simpler as they don't have to apply any of the
> > > "built-in"
> > > > equivalence rules themselves. They just have to make 
> sure that they
> > > > resolve the one canonical form...
> > > >
> > > > 	-Gabe
> > > >
> > > > > -----Original Message-----
> > > > > From: Dave McAlpin [mailto:dave.mcalpin@epokinc.com]
> > > > > Sent: Tuesday, November 11, 2003 10:50 AM
> > > > > To: xri-editors@lists.oasis-open.org
> > > > > Subject: [xri-editors] XRIs and canonical form
> > > > >
> > > > >
> > > > > I've been asked to draft text specifying a "canonical form"
> > > > > for XRIs. I
> > > > > wanted to start by understanding what canonical form
> > > meant for URIs in
> > > > > general, and in searching the web I came across the following
> > > > > exchange. The
> > > > > initial question is from Terence Spielman of Visa, followed
> > > > > by Gabe's and my
> > > > > responses. Just interesting that we've considered this
> > > > > question before.
> > > > >
> > > > > Dave
> > > > >
> > > > > >>>In addition, aside from unresolvable references, 
> is it possible
> > > > > >>> to canonicalize XRIs?  This is a highly desireable feature
> > > > > >>> (for equivalence, at a minimum).
> > > > >
> > > > > >>We talked quite a bit about this. The decision was made to
> > > > > be silent on
> > > > > >>canonicalization because equivalence is actually
> > > > > unambigious given the
> > > > > >>rules stated. Now, that doesn't mean that its at 
> all obvious.
> > > > > >>
> > > > > >>I do think giving names to the escaped vs. unescpaed forms
> > > > > of XRI, at
> > > > > >>least, would be useful.  Canonicalization would then just
> > > > > be transforming
> > > > > >>an identifier into one of those forms. We didn't want to
> > > > > mandate a single
> > > > > >>canonical form because different environments would need
> > > > > XRIs in different
> > > > > >>levels of escaping and it would be unfortunate to
> > > require a specific
> > > > > >>canonicalization form that would require otherwise-unneeded
> > > > > transformation.
> > > > > >>
> > > > > >>Again, Dave McAlpin probably has better input on this.
> > > > >
> > > > > >A canonical representation might be useful for comparison,
> > > > > but it would
> > > > > >involve a formal definition of things like "minimally
> > > > > escaped", which would
> > > > > >be fairly difficult to nail down. It would also depend on
> > > > > the existence of
> > > > > >a canonical form for URIs used as cross-references. In other
> > > > > words, an XRI
> > > > > >wouldn't have a canonical form if it contained
> > > > > cross-references that didn't
> > > > > >define a canonical form.
> > > > > >
> > > > > >Note that equivalence rules are generally problematic. The
> > > > > IRI proposal,
> > > > > >for example, completely dodges the question of equivalence
> > > > > when it says,
> > > > > >"There is no general rule or procedure to decide whether two
> > > > > arbitrary IRIs
> > > > > >are equivalent or not... Each specification or application
> > > > > that uses IRIs
> > > > > >has to decide on the appropriate criterion for IRI
> > > > > equivalence." 2396bis
> > > > > >notes that even terms like "different" and "equivalent" are
> > > > > fuzzy in the
> > > > > >general spec and ultimately application dependent.
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
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> 


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