RE: [ubl-dev] Re: Global elements doing UBL a disservice

["G. Ken Holman" <gkholman@CraneSoftwrights.com>]

At 2006-05-31 09:07 +0800, Chin Chee-Kai wrote:
>Agree with you, David.  I'm saying the same, that XSD can even handle
>very well those (SQL) schemas, which also handled very well the storage
>needs for EDI in the EDIFACT days (prevailing now still...).

Right ... because SQL is designed for database tables, and EDI is 
designed around messages.

>Yet, now there's a likely proposal from Ken that XSD cannot handle
>UBL's infoset, and thus a need for RELAX-NG.  This is what I thought
>is both puzzling, and somewhat worrying.

I'm not sure why ... from day one we've said that UBL takes a 
"document approach" to the encoding of the information of business 
documents, not a message or database approach.  To me that means text 
processing and there is a long history of text processing that is 
quite different than program-to-program data exchange.

>On re-reading what I wrote for that paragraph, I think I might not
>have ubl:qualified my pronouns properly.  It probably should read,
>
>"Why did, and when have, the structures of the EDI datasets become
>suddenly so complicated that XSD, which can even describe SQL database
>schemas, cannot now describe those EDI datasets?"

Because when XSD hijacked XML and redefined the text-processing roots 
of SGML to be program-to-program abstract-value transmission and 
reception supporting programs and databases, some basic functionality 
for raw text processing was not addressed.

I wasn't proposing RELAX-NG just because I'm a RELAX-NG bigot ... we 
have real requirements in UBL *that the designers of XSD did not 
accommodate* but that technologies such as RELAX-NG happen to 
accommodate.  RELAX-NG was created based on 1960's-era hierarchical 
database theory that has been applied to hierarchical XML documents, 
and its validation semantics are published as part of the 
specification, thus making incorrect implementation impossible (if 
you implement the semantics as written) because there is no 
"interpretation" of the standard to be made.

For example, RELAX-NG is closed under union, thus if I make a 
database query from two data sets I can *programmatically* express 
the document model of the result set from that database query and 
validate the result set using it ... that is not possible in XSD in 
the general case.  In XSD I cannot programmatically create an XSD 
model of the result set of a query of two data sets described by XSD 
models ... it requires hand-crafting.

So, from the start of UBL we said we were taking a document-oriented 
approach to our description of business documents ... to me that 
means a text-processing approach that supports access by programs 
because of interfaces to XML instances ... I'm just showing that XSD 
does not handle all of the requirements as our requirements evolved 
from UBL 1.0 (which it did handle) to UBL 2.0 (which it does not 
handle).  I don't think we should lose functionality and opportunity 
in UBL 2.0 because of the deficiencies of XSD.  I'm going to document 
the methodology and what it will take to use XSD (which appears right 
now to require NVDL since XSD can't express the requirement).

Trust me, Chee-Kai, that I have tried very hard to address the 
clamour for a pure-XSD solution with respect to extensions.  I'm 
being told in XML Dev and in W3C Schema that what I want to do cannot 
be done in XSD.

I'll leave it with Steve and Joe to summarize the issues of redefine 
and substitution since they are obviously more qualified and 
experienced to summarize their problems ... I'm focused right now on 
extension.  There are so many special cases and exceptions in XSD 
that I really have lost the thread on the problems that they were 
describing.  And it was with your help that I realized that I didn't 
understand what was going on ... it is more dangerous to think I was 
understanding when I was not, so I do appreciate that.

For every group of users that I'm talking with regarding extension, 
they are asking me to come up with a pure XSD solution to our 
requirement, but how can I give that to them when XSD semantics do 
not support our needs?

Thanks, Chee-Kai!

. . . . . . . . . . . Ken

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