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Re: Motivations for restricting the "all" group

From: Pete Cordell <petexmldev@codalogic.com>
Date: Thu, 28 May 2009 11:31:42 +0100
Message-ID: <4BBBA7EF49E045338B19CFCE0944A935@Codalogic>
To: "Dag Hovland" <dag.hovland@uib.no>, <xmlschema-dev@w3.org>
I wasn't on the committee that developed XSD 1.0 (or XSD 1.1), but from 
other discussions on various e-mail lists I get the impression that they 
were concerned about the implementability of various features using finite 
state machines, especially without counters within states etc.  I think an 
xs:all with unrestricted cardinalities for members gets particularly hungry 
for states when implemented this way, hence the restrictions.

I think the feeling now is that there are other, non-state machine ways to 
implement validation of constructs such as xs:all with unrestricted 
cardinality and so the restrictions are relaxed.

HTH,

Pete Cordell
Codalogic Ltd
Interface XML to C++ the easy way using XML C++
data binding to convert XSD schemas to C++ classes.
Visit http://www.xmldatabinding.net for more info
----- Original Message ----- 
From: "Dag Hovland" <dag.hovland@uib.no>
To: <xmlschema-dev@w3.org>
Sent: Thursday, May 28, 2009 7:53 AM
Subject: Motivations for restricting the "all" group


>I have been trying to do some research into regular
> expressions and the "all" group used in XML Schema, as
> mentioned in
>
> http://www.w3.org/TR/2001/REC-xmlschema-0-20010502/
>
> It is clear that "all" is in some sense restricted, since it can only
> combine elements, and must appear at top level. My question is, what was
> the original inspiration for "all", what is the "unrestricted" form of
> "all", and why was it originally restricted, in the design of XML Schema?
>
> Some academic authors claim that "all" is a restricted form of
> "interleaving", a known operator in regular language theory, for which
> the membership problem is NP-complete. But this is not clear to me, as
> interleaving means that the words are shuffled in a way that does not
> seem to make sense for natural languages. I believe that the "&" from
> SGML is a more natural extensions, but I cannot find any reference to
> the original motivation, or to the reasons for limiting "all".
>
> Thank you for any help,
>
> Dag Hovland
> 
Received on Thursday, 28 May 2009 10:32:37 GMT

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