RE: [xri] POLL: Syntax 2.0 or 2.1

["Drummond Reed" <drummond.reed@cordance.net>]

Steve (and everyone on this thread),

I think we are talking past each other RE what I'm saying about the role of
XRIs and XDI RDF. XDI RDF doesn't do anything to change the RDF graph model,
that's why it's called XDI RDF. Everything is triples. It does, however, use
a different serialization model than RDF, and the primary reason it does
that is *addressing*. As Bill Barnhill so well summarized it at our f2f
meeting, the XDI RDF model has three breakthrough features over conventional
RDF:

1) No blank nodes.
2) Automatic reification.
3) All statements are identifiers and all identifiers are statements.

All three of these features are a direct result of the core design principle
of XDI (in both the ATI and RDF models): 100% addressability of all nodes in
the graph. In fact, in the XDI RDF model, not just all nodes addressable,
but all XDI statements (arcs) are addressable -- even the refs (in the XDI
ATI model, we needed a workaround to make refs addressable).

In short, THE killer feature of XDI RDF is addressing, which depends
completely on XRIs. In particular, it depends on the ability of XRI to
compose identifiers out of other identifiers -- both global and local
identifiers.

When it comes to addressing, the value of direct concatenation to the XDI
RDF model is the simplicity of the XRIs used to address nodes in the XDI RDF
graph. In response to Gabe's earlier note about "having these requirements
in front of us", I have repeatedly tried to make sure everyone on the XRI TC
was aware of how significant this factor is by pointing them to the very
detailed XDI RDF proposal, currently in its fourth version:

http://www.oasis-open.org/committees/download.php/23161/xdi-rdf-model-v4.pdf

This is the XDI addressing model that I have been referring to throughout
the development of XRI Syntax 2.1. If you have not read this document, I
strongly urge you to take the time to read through it and look over the
example XDI documents (in four serialization formats, no less) and the XDI
addresses they contain. I think they provide very rich examples of the
dramatic difference that direct concatenation makes in the simplicity of XDI
RDF addresses. 

By simplicity, I mean two things:

1) Human-readability and understandability, which has a huge amount to do
with adoption by developers, directory administrators, and other IT
personnel who (we hope) will be dealing with XDI addresses on a day to day
basis (just like they deal with IP addresses, domain names, and URIs on a
daily basis), and for whom human-readability and understandability is a
serious factor in adoption (witness HTML).

2) Comparability, i.e., the ability to take two XRIs and compare them
without complex normalization rules.

Since this topic is so important (why else would I be typing this late into
the night...), let me provide a detailed example from the document I cited.
The following is an XDI RDF address of an attribute of one of my personal
persons, expressed using the direct concatenation in the XRI Syntax 2.1
proposal:

#1:	=drummond+work/+person+name+first

Now, here's the closest address that one could TRY to compose that expressed
the same relationships using 2.0 syntax:

#2:	=drummond*(+work)/(+person*(+name*(+first)))

I emphasize "TRY to compose" because the grammar expressed in the second
address is NOT EQUIVALENT to the first one. That's what I was trying to
explain in the f2f meeting: global-xrefs, the ABNF rule that enables direct
concatenation (see http://wiki.oasis-open.org/xri/XriCd02/XriAbnf2dot1) are
not a "compact" way of expressing local-xrefs, as I (and all of us) first
thought. As Les puts it, they are a different grammatical construct than a
local-xref, because they are a reference to a resource in a global context
vs. a local context. (To use an English language analogy, this is like the
difference between saying "Drummond Reed" and "Drummond's Reed".
Grammatically they are very different.)

That point alone is very important, but back to my original point: look at
these two addresses. See how intuitive #1 is. Here at the Higgins f2f, folks
who had never worked with XRI have been able to just go to the whiteboard
and write one without thinking.

Now, imagine them trying to do that for #2.

Yes, I know you can make a case (as Wil has) that "most people will not need
to understand XRI syntax". And you can also make a case (as Steve has) that
"global xrefs add complexity to XRI parsing and resolution". But I hope you
can understand why I am pushing back so hard on those arguments. It's not
that I don't understand them -- I do. 

It's that I believe they don't outweigh the tremendous intuitive and
expressive power of direct concatenation. Besides being brain-dead easy to
read, it gives any person who knows how to type the ability to tag an XRI
just by adding "+tag". To say we shouldn't do this because we didn't
understand how this would possible in earlier versions of XRI syntax (which
is the absolute truth -- do you think that if we had seen this in XRI 1.0 or
2.0 we would not have done it??) would be the TC equivalent of saying, "Yes,
cars may be faster than horses but they are more complex and require
gasoline and spew exhaust, so let's just stick with horses."

That's as much as I can put in an email tonight (though I'm doubtful email
will be very productive towards resolving this issue). I'll schedule it for
Thursday's telecon.

=Drummond 



-----Original Message-----
From: Steven Churchill [mailto:steven.churchill@xdi.org] 
Sent: Tuesday, May 01, 2007 6:25 PM
To: 'Drummond Reed'; 'Tan, William'; 'Gabe Wachob'
Cc: xri@lists.oasis-open.org
Subject: RE: [xri] POLL: Syntax 2.0 or 2.1


Drummond,

It strikes me as funny that you continue to use XDI RDF as the motivation
for adding complexity to the abstract models of XRI syntax and authority
resolution. It is ironic, because I think you have failed to take away one
of the most important lessons that the RDF folks have to offer: that of the
importance of a foundation based upon a solid and simple abstract model.

I urge you to take a look at the normative document "RDF Concepts and
Abstract Syntax" <http://www.w3.org/TR/rdf-concepts/>. If you do, you may
note the following:

1. 	The RDF abstract graph model IS formally defined. (Kudos to them!)
See section 3.1 "Graph Data Model". The XRI/XRI TCs have consistently
"avoided" formally defining their abstract syntax and graph models.

2.	The incredible simplicity of the RDF graph model. This is by design,
not by accident.

3. 	Note the language of section 2.2.4: "RDF has a recommended XML
serialization form [RDF-SYNTAX], which can be used to encode the data model
for exchange of information among applications." 
To the RDF folks, the serialization format is not the "heart" of the
specification -- it is a recommendation. If only RDF XDI could take away
that lesson and focus on its graph model instead of its serialization
format! 

So you keep using (XDI) RDF as a motivation for adding complexity to the XRI
models. I personally consider RDF as a perfect example of why we should NOT
do so.

~ Steve



-----Original Message-----
From: Drummond Reed [mailto:drummond.reed@cordance.net] 
Sent: Tuesday, May 01, 2007 3:44 PM
To: 'Tan, William'; 'Gabe Wachob'
Cc: xri@lists.oasis-open.org
Subject: RE: [xri] POLL: Syntax 2.0 or 2.1

Again, I want to make sure it's clear why this is such a big issue: the XDI
RDF model uses the "grammer" of global-xrefs. This "grammer" cannot be
duplicated (at least in any easy way I can figure out) by "going back" to
2.0 syntax.

So this issue is deep, deep, deep.

=Drummond 

-----Original Message-----
From: Tan, William [mailto:William.Tan@neustar.biz]
Sent: Tuesday, May 01, 2007 3:33 PM
To: Gabe Wachob
Cc: xri@lists.oasis-open.org
Subject: Re: [xri] POLL: Syntax 2.0 or 2.1

Yes. Xrefs can only appear within parentheses.

Gabe Wachob wrote:
> Can you spell out the implications of this choice so we know exactly 
> what
it
> is we are voting for/against? 
>
> That is, we are saying that XREFs basically stay as is and that the 
> @foo+bar+baz syntax goes away?
>
> 	-Gabe
>
>   
>> -----Original Message-----
>> From: Tan, William [mailto:William.Tan@neustar.biz]
>> Sent: Tuesday, May 01, 2007 3:25 PM
>> To: xri@lists.oasis-open.org
>> Subject: [xri] POLL: Syntax 2.0 or 2.1
>>
>> We did an informal poll at the f2f two weeks ago on whether we should 
>> stick with XRI Syntax 2.0. I suggest we vote again on the list.
>>
>> +1 - to support concatenated syntax
>> 0 - don't care
>> -1 - no concatenated syntax
>>
>> I'm reverting my vote to -1 because the solution is too confusing IMHO.
>>
>> =wil
>>     
>
>
>