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Subject: Important topic for tomorrow's XDI TC telecon: ABNF single delimiter level proposal

I'm sending this in addition to the usual agenda message (coming next) to highlight one specific proposal on the agenda for tomorrow's call: the ABNF "single delimiter level proposal".

The origins go back the conversation on last week's call about a dedicated UUID syntax, and then subsequent discussion between Markus and Joseph and I about the role of delimiters in the ABNF.

What we realized was that the longstanding assumption (from the ancient history of XRI) that we needed a "global" and "local" level of identifiers -- and thus different combinations of global and local delimiters to express different semantics -- was actually causing more complexity and confusion than it solved (as anyone who has tried to memorize multiplicity syntax knows).

So we had a simple idea: what if we eliminated the two levels of delimiters and just went down to a single level in which each delimiter had exactly one precise semantic meaning and none of them are overloaded with multiple meanings in different contexts?

What this requires, of course, is introducing a few new delimiters -- four, to be precise (to represent the four multiplicity options besides entity singletons, which are the default and require no special syntax).

But once we worked out what those four should be, the result (in my personal opinion) is significantly simpler than the double-delimiter+cross-reference rules that we had before. Plus it's much more regular. Every subsegment/subgraph in an XDI address is either:
  1. delimiter + literal string
  2. delimiter + cross-reference (which repeats the pattern)
In any case, if you have time before the call, please review the proposal which is the latest comment (labeled Drummond Reed 2013-03-13) on https://wiki.oasis-open.org/xdi/XdiAbnf/Discussion, and I look forward to discussing this on the call.


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