OASIS Mailing List ArchivesView the OASIS mailing list archive below
or browse/search using MarkMail.

 


Help: OASIS Mailing Lists Help | MarkMail Help

xri-editors message

[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]


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.
> >
> >
> >
> >
> >
> > To unsubscribe from this mailing list (and be removed from
> > the roster of the OASIS TC), go to
> > http://www.oasis-open.org/apps/org/workgroup/xri-editors/membe
> rs/leave_workgroup.php.
> 
> To unsubscribe from this mailing list (and be removed from the roster of
> the OASIS TC), go to http://www.oasis-open.org/apps/org/workgroup/xri-
> editors/members/leave_workgroup.php.





[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]