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Subject: RE: [xri] Proposal for XRI Syntax 2.1 to treat all delimiters as signficant
I personally don’t see it as *significantly* easier. However, if
the rest of the TC does that is fine. I do feel that saying two XRIs,
that are different only in the parens, are not the same is confusing. Why should =drummond+phone be
different than =Drummond*(+phone)? From: Drummond Reed
[mailto:drummond.reed@cordance.net] Les, Marty, see [=Drummond] inline in both
your messages below. From: Chasen, Les
[mailto:les.chasen@neustar.biz] I think you and I are mostly in agreement on the use
of parens. The thing I don't understand is how removing the parens in a
cross reference makes it significantly easier for humans to read and write
XRIs. [=Drummond] I believe the
motivations for the global ref proposal is very simple and clear: it allows you
to concatenate two or more single-segment absolute XRIs directly, with no
special rules about the use of delimiters or parentheses. For example, take the following XRIs, all
of which are independently syntactically valid absolute XRIs: =drummond +phone +work $v*3 Under the global refs proposal, you can
compose composite XRIs out of these component XRIs via direct contatenation
without any special rules. Examples: =drummond+phone =drummond+work =drummond+phone+work =drummond+phone$v*3 =drummond+phone+work$v*3 =drummond+phone$v*3+work$v*2 I suspect that XRI TC members have been
working with parenthetical encapsulation of cross-references for so long that
the notion of direct concatenation of global references seems foreign. However
my experience with individuals outside of the TC is exactly the opposite. Since
they’ve never seen parenthetically-encapsulated identifiers, direct
concatenation is completely intuitive to them, whereas the concept of
parenthetially-encapsulated identifiers is foreign and must be learned. I would go so far as to say that direct
concatenation of identifiers is so simple, intuitive, and useful that as a TC
we should be taking the opposite stance and asking how can we ELIMINATE the
need for parenthetical encapsulation wherever possible. When you take this
perspective, the places where we have found parenthetical encapsulation is
unavoidable is: * Using URIs as cross-references (because
URIs have a different syntax) * Using multi-segment XRIs as
cross-references (because you need to know where the cross-reference ends) * Using multiple cross-references as a
single cross-reference (because you need to know where the cross-reference
ends) Direct concatenation works in all other
cases, so I submit that these should be the only three cases where
parenthetical encapsulation is necessary. See more [=Drummond] inline in
Marty’s message below.
[=Drummond] Correct. By
the logic above, if an XRI author has a reason to not use direct concatenation
where it would be syntactically valid, that reason is known to the author and
should not be overrided by XRI normalization rules.
[=Drummond] While I
understand this sentiment, I believe it needs to be weighed against the
simplicity and intuitiveness of direct concatenation. I doubt anyone on the TC
would argue that direct concatenation is the simplest and most intuitive method
of identifier construction there is. After all, every single sentence I’m
writing here is composed of directly concatenated words (where spaces are the
delimiter). [=Drummond] I’ll go
on record as saying that I believe the TC would be making a tremendous mistake
if, simply because of our evolutionary path in figuring this all out, we ignore
the power of direct concatenation in the construction of XRIs. I can’t
count the number of times that developers, when first exposed to XRI syntax,
have asked me, “Can’t you get rid of those complicated
parentheses?” [=Drummond] But you
don’t need to take my word for it. If it would be more scientifically
objective for us to get the opinions of developers, Internet architects, and
others outside the TC about the relative value of direct concatenation vs.
parenthetical encapsulation, I’d be happy to help organize a feedback
session. I still suggest that [=Drummond] Ironically,
the proposed normalization rule – that all delimiters be considered
significant – already tells you that these three XRIs are not equivalent. This seems intuitive [=Drummond] Although I
too have been tempted by a mathematical interpretation of parentheses in the
past, I now believe its a red herring. Identifiers are not operators. They are
identifiers. They identify resources using a sequence of characters. Therefore
the fewer normalization rules that are necessary to change this sequence of
characters, the better.
[=Drummond] Agreed. I
believe that the syntax in http://wiki.oasis-open.org/xri/XriCd02/XriAbnf2dot1
is the most precise we’ve ever had, and the corresponding normalization
rules are the simplest we’ve ever had.
[=Drummond] All the
proposed 2.1 ABNF states is that a ref-value to be optional, which is no
different that the 2.0 ABNF. An empty ref-value is no different than an empty
subsegment or an empty segment. We didn’t invent the concept of an empty
segment -- URI and IRI have long explicitly supported that concept. In URI and
IRI syntax, every segment contains a ref-value (they don’t call it that,
but it’s the same thing), and it’s not required, so it can be
empty. [=Drummond] There are
many uses for an empty segment, although I would say that few if any of them
are “intuitive”. Like the number zero, its inherently a complex
concept.
[=Drummond] I strongly
believe that at this point we need to generalize from specific use cases to
general principles. We have spent several years developing XRI syntax to meet
an overall set of design principles. The proposal at http://wiki.oasis-open.org/xri/XriCd02/XriAbnf2dot1
is the simplest and most general ABNF we’ve ever had. To Steve’s
point, it is now as close to a completely abstract syntax as we have been able
to get. [=Drummond] The key point
I’m trying to make it that designing the syntax to the Einsteinein
dictate of “as simple as possible but no simpler” means that we
will have done our best to design a syntax that can be adapted to hundreds of
future use cases for identifiers that we have never anticipated, just as we
have use cases today that we never anticipated three years ago. To use
parenthetical encapsulation as an example: who are we to say to say to the XDI
TC – or any any future producer of XRIs and XRI-based identifier
construction algorithms – that double or triple or quadruple parentheses
should not be significant? The fact that the XDI TC was the first to come up
with that usage reinforces for me the importance of keeping the rules as simple
as possible: if all delimiters are significant, then its very clear what XRIs
can be evaluated as equivalent directly vs. what XRIs must be evaluated as
synonyms via local policy or resolution.
[=Drummond] Again, by the
current proposed normalization rule, none of the four XRIs above are
equivalent. To begin with, they all state that the resource is being identified
in a different global context, so that rules out syntactical equivalence. It would
almost be like saying =drummond and @cordance*drummond should be syntactically
equivalent. They might be proven to be synonyms in that they identify the same
resource via resolution, yes, but to say anything about syntactical equivalence
of identifiers that are not syntactically equivalent outside of a set of very
narrow normalization rules is something I think we should avoid at all costs.
[=Drummond] Unfortunately
that kind of special exception is antithetical to the concept of a simple,
generalized syntax for XRIs. See my next message to the list regarding this
point, as I believe it’s critical to coming to closure on XRI Syntax 2.1. =Drummond |
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