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Re: ASN.1 => XML Schema questions

From: Geoff Elgey <elgey@dstc.qut.edu.au>
Date: Wed, 27 Jun 2001 16:42:28 +1000
Message-ID: <3B398054.3888E01B@dstc.qut.edu.au>
To: Martin Duerst <duerst@w3.org>
CC: xmlschema-dev@w3.org
G'day,

Martin Duerst wrote:
> Well, the problem isn't with a particular syntactic construct,
> such as <all>, but with the idea that you want to have a
> sequence of sets. If the sets have common elements (true in
> your case, because the sets are always subsets of the same
> base set), and if elements can be missing (true for anything
> the merrits the name 'set'), then you get these ambiguities
> in any case.
> 
> I'm very curious how ASN.1 solves this problem.

The encoding rules (such as BER/DER) explicitly specify (using a tag and
length) each particular SET within a SEQUENCE. So the ambiguous string
"xyzyx" would actually be something like  "{ {xy},{zyx} }" under
BER/DER, so that there are no ambiguities in its interpretation.

I was hoping to achieve the same result by using <all>* for a sequence
of sets, but there are still ambiguities. I'll use another method for
representing sequence of sets, that explicitly delimits each set.

Cheers,
Geoff
-- 
Geoffrey Elgey ph: +61-7-38641487  Distributed Systems Technology
Centre  
Security Unit  fax:+61-7-38641282  QUT, Brisbane, Australia   
                   http://www.dstc.edu.au 
DSTC is the Australian W3C Office  email: elgey@dstc.edu.au
Received on Wednesday, 27 June 2001 02:42:34 GMT

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