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Subject: RE: [xri] Updated 2.1 ABNF and global subsegments
Les, We didn’t “factor out”
xrefs. The refactored ABNF I just posted this morning at… http://wiki.oasis-open.org/xri/XriCd02/XriAbnf2dot1 …doesn’t propose any change to
the ABNF parse tree, only changes to the ABNF rule names so that we eliminate
semantic confusion over what we mean by the term “cross-reference”
or “xref” for short. The key problem that several TC members besides
yourself pointed out when reviewing the 2.1 ABNF is that in the 2.0 ABNF we had
only one concrete ABNF rule (to use Steve’s terminology) that instantiated
the abstract concept of a cross-reference. That was the “xref”
rule. In the 2.1 ABNF we have two concrete ABNF
rules that instantiate this concept, and calling only one of them “xref”
was thus causing confusion. The semantic solution I hit upon was to
call both of them “-refs” (which they are). What was formerly “xref”
is proposed to be “encap-ref” (for “encapsulated reference”)
and the other form is a “global-ref” (which is one of the two forms
of XRI subsegments, the other being “local-ref”). So now the spec can explain, in the text,
what I believe is the single most important feature of XRI syntax – the abstract
concept of cross-references – and then refer to the two ways in which it
is concretely instantiated in the ABNF, as either a global-ref or an encap-ref. =Drummond From: Chasen, Les
[mailto:les.chasen@neustar.biz] I am not sure it makes sense to completely
factor out xrefs. Cross references are a very well baked concept in the
XRI specifications. To remove it seems rather drastic and a large
change. If you really want to make parenthesis optional in a xref why can’t
you just make them so with [“(“][“)”] or something. From: Drummond Reed
[mailto:drummond.reed@cordance.net] Good points/questions, Les. See
[=Drummond] inline. From: Chasen, Les
[mailto:les.chasen@neustar.biz] A couple of note/comments: * another change that this includes but does
not spell out is that ! is no longer a GCS character. [=Drummond] Good point. Standard Example
#10 on http://wiki.oasis-open.org/xri/XriCd02/GlobalSubsegments
shows what happens under this proposal – the former ! GCS character
(which by the XRI 2.0 ABNF had to be followed by a second !, so effectively it
was always !!) is now a subspace under another GCS character. For example, the
XDI.org !! registry would become a subspace of the @ registry, i.e., !!1000
would become @!!1000. * One thing that confuses me is that the
second instance of a global-subseg is a xref without parenthesis but is not
called a xref. [=Drummond] That’s a good point that
was also brought up by Laurie and Marty on our XRI $ Dictionary calls.
It’s purely a semantic issue, but an important one. I went back and
studied the v3 proposal ABNF closely, and I came up with a solution I really
like: remove the usage of “xref” altogether. See my next message to
the list with a full explanation of the v4 I just posted at http://wiki.oasis-open.org/xri/XriCd02/XriAbnf2dot1.
* In this example =$d*2006-02-17=example
how does that compare to =($d*2006-02-17=example)
and =($d*2006-02-17)=example and =$d*2006-02-17(=example) and =($d*2006-02-17)(=example).
Do these all mean the same thing? [=Drummond] Marty and I went over this
same question on our XRI $ Dictionary call yesterday. The first thing I need to
point out is that, although we discussed not needing a delimiter before
parentheses in the 2.1 ABNF, for good reasons Marty and I discovered, we do
need to require one (either a GCS or LCS character). So the last two XRIs in
your question should be =$d*2006-02-17*(=example) and =($d*2006-02-17)*(=example). [=Drummond] On the question of whether
they all “mean the same thing”, there are two possible answers: a)
yes, they represent the same resource because they *normalize to the same XRI*, or b) they MIGHT represent the
same resource (i.e., be synonyms), but that can only be determined via
resolution. [=Drummond] For good reasons which
we’ll talk about on tomorrow’s call, right now my answer would be
the latter. But I plan to discuss this with Marty further before then (and if
we come to solid conclusion, we’ll post it). =Drummond From: Drummond Reed
[mailto:drummond.reed@cordance.net] XRI TC Members and Observers: An update to the proposed ABNF for XRI Syntax 2.1 has been
posted to the XRI TC wiki at:
http://wiki.oasis-open.org/xri/XriCd02/XriAbnf2dot1 This third draft incorporates feedback and suggestions from
earlier drafts. In particular it now breaks the former xri-subseg (XRI
subsegment) rule into two forms: global-subseg (global subsegment) and local-subseg
(local subsegment). Global subsegments replace the former compact syntax
proposal. A full explanation of global subsegments and how they would be
treated by XRI resolution has been posted at:
http://wiki.oasis-open.org/xri/XriCd02/GlobalSubsegments Note that the latter page still has a few TO-DOs at the end
which I’ll fill in tomorrow. But I urge you to review both the proposed
ABNF and the global subsegment proposal in preparation for this
Thursday’s call. Also, in a call I had with Les and Wil and Trung today, Wil
took the action item to review the ABNF from the standpoint of the OpenXRI
parser implementation. So he may come back with suggestions about how rule
names might be refactored to best support implementation. Please do send any feedback/comments directly to the list,
as this is the last major outstanding issue for XRI Syntax 2.1, so we want to
close on this and begin drafting as soon as we can to be ready for final review
at the OASIS Symposium starting April 16. =Drummond
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