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Re: ASN.1 => XML Schema questions

From: Geoff Elgey <elgey@dstc.qut.edu.au>
Date: Mon, 25 Jun 2001 18:24:15 -0400 (EDT)
Message-ID: <3B37B9F3.30AFE052@dstc.qut.edu.au>
To: vdv@dyomedea.com
CC: xmlschema-dev@w3.org
G'day,

Eric van der Vlist wrote:
> > 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>
> 
> What's wrong with the above?
> 
> IMHO, it's exactly doing what you want to achieve.

I was wondering of there was a simply method of declaring aliases,
rather than defining a restriction/extension. An alias would be of a
form similar to:

<typeAlias name="INTEGER" ref="integer"/>

I also found I had to do the following when aliasing a complex type:

<xsd:complexType name="ResourceReport">
  <xsd:complexContent>
    <xsd:restriction base="EXTERNAL"/>
  </xsd:complexContent>
</xsd:complexType>

rather than:

<xsd:complexType name="ResourceReport">
  <xsd:restriction base="EXTERNAL"/>
</xsd:complexType>

(Note: I'm using XML Authority for schema checking here)

So a simple methodfor aliasing a type would be most welcome.

> I just find confusion prone the fact to rely on upper/lower cases to
> distinguish between your INTEGER and W3C XML Schema's interger and I
> would personaly use a different namespace.

Agreed -- the above is for example purposes only.
 
> > 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?
> 
> Yes, the workaround for this is:
> 
> <complexType>
> <choice minOccurs="0" maxOccurs="unbounded">
>   <element name="a" type="integer"/>
>   <element name="b" type="boolean"/>
> </choice>
> </complexType>

Not quite -- the above definition is for (a|b)*, but I'm looking for
definitions of the form (ab|ba)*.

In fact, expanding this to the general case of N elements, there would
be N! alternatives in the content, with [0..unbounded] occurrences of
any particular alternative.

I know that N! alternatives sounds daunting when performing schema
validation -- is this why <all> cannot have repetitions or be nested
within a <sequence> ?

However, at first glance the algorithm for distinguishing alternative
boundaries seems workable -- read tags until either (a) each element
from the set has been found or (b) a repetition of an element is found,
whichever comes first. Then validating of presence/absence of particular
elements within the set can occur.

But such an algorithm probably would not work for <all> nested within
<all>.

Comments? Suggestions?

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 Tuesday, 26 June 2001 03:46:01 GMT

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