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ASN.1 => XML Schema questions

From: Geoff Elgey <elgey@dstc.qut.edu.au>
Date: Mon, 25 Jun 2001 00:36:36 -0400 (EDT)
Message-ID: <3B36BFC8.DAE775F2@dstc.qut.edu.au>
To: xmlschema-dev@w3.org
G'day,

[I've been looking through the archive and published standards but I
didn't find anything on this topic.  Apologies if this has been
discussed before or is an a FAQ]

I'm playing around with an ASN.1 to XML Schema translator, and most of
the translations seem okay, except for the following:

a) Aliasing a global type

ASN.1 defines an INTEGER type, and I'd like to use a type called
"INTEGER" rather than blindly substituting the equivalent XML Schema
type "integer". That is, define a type called "INTEGER" that aliases the
"integer" type.

The best I could come up with was:

<simpleType name="INTEGER">
  <restriction base="integer"/>
</simpleType>

Is there a simply method of defining type aliases?



b) Repetition of <all>

In ASN.1 we can define a SET type, such as :

T1 ::= SET { x INTEGER, y BOOLEAN } 

where a SET is a type whose elements can come in any order. 

So looking at the XML Schema documentation, I can define this as
follows:

<complexType name="T1">
<all>
  <element name="x" type="integer"/>
  <element name="y" type="boolean"/>
</all>
</complexType>

There are also list types in ASN.1, such as the following:

T2 ::= SEQUENCE OF T1

This declares T2 to be a list of T1, and so a possible XML Schema for T2
is:

<complexType>
<sequence minOccurs="0" maxOccurs="unbounded">
  <element name="T1" type="T1"/>
</sequence>
>/complexType>

However, it is also possible in ASN.1 to have a list of anonymous SET,
such as:

T3 ::= SEQUENCE OF SET { a INTEGER, b BOOLEAN }

But it appears that neither of the following types are legal in XML
Schema:

<complexType>
<all minOccurs="0" maxOccurs="unbounded">
  <element name="a" type="integer"/>
  <element name="b" type="boolean"/>
</all>
</complexType>

==> illegal because <all> can only have min & max of 0 or 1

<complexType>
<sequence minOccurs="0" maxOccurs="unbounded">
  <all>
    <element name="a" type="integer"/>
    <element name="b" type="boolean"/>
  </all>
</sequence>
</complexType>    

==> illegal as <all> cannot be nested within <sequence>

Is there any way to specify in XML Schema that a collection of elements
that can appear in any order, and that each such collection can occur
multiple times?

Any help greatly appreciated.

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 Monday, 25 June 2001 03:23:40 GMT

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