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Subject: RE: [xri-editors] XRIs and canonical form
What about removing $! and ! cross-references? -Gabe > -----Original Message----- > From: Dave McAlpin [mailto:dave.mcalpin@epokinc.com] > Sent: Wednesday, November 12, 2003 11:18 AM > To: 'Wachob, Gabe'; xri-editors@lists.oasis-open.org > Subject: RE: [xri-editors] XRIs and canonical form > > > I'll clean it up before I incorporate it into the spec, but I > just wanted to > see how people felt about the kind of non-normative, guidance > tone this > takes. > > In general, XRIs do not have a single canonical form. This is > especially > true for XRIs that contain non-XRI cross-references, since > many URI schemes > do not define a canonical form. HTTP URIs, for example, do > not have a single > canonical form. It is therefore true by definition that an XRI with a > cross-reference containing an HTTP URI does not have a single > canonical > form. With that said, it is valuable to define guidelines for > making XRIs > reasonably canonical. XRIs that follow these guidelines will be more > consistent in presentation, simpler to process and less prone to > false-negative comparisons. > > Absent a compelling reason to do otherwise, those who > generate or reference > XRIs should provide them in a form in which > > - The optional xri scheme is added > - The scheme is provided in lowercase > - The optional leading dot in xri-segments is omitted > - Percent-escaping uses uppercase A through F > - The authority component is in lowercase > - Unnecessary escaping is removed > - /./ and /../ are absent in absolute XRIs > - Cross-references are reasonably canonical with respect to > their schemes > > Examples > > Non-canonical Canonical Comment > @example xri:@example Add optional scheme > XRI:@example xri:@example Lowercase scheme > xri:@example/.abc xri:@example/abc Remove optional > leading dot > xri:@example%2f xri:@example@2F Uppercase when > percent escaping > xri:@Example xri:@example Lowercase authority > xri:@ex%61mple xri:@example Remove > unnecessary escaping > xri:@example/./abc xri:@example/abc Resolve /./ and /../ > > > -----Original Message----- > > From: Wachob, Gabe [mailto:gwachob@visa.com] > > Sent: Tuesday, November 11, 2003 12:47 PM > > To: 'Dave McAlpin'; Wachob, Gabe; xri-editors@lists.oasis-open.org > > 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. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > 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. > > > > > > > > > > > > > > > > > > > > > > > > > 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. > > > > > > > > > > > > > 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.
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