Michael, you are exactly right. I think I figured it out, though:

  <xsd:element name="parent">
   <xsd:complexType>
    <xsd:choice>
      <xsd:sequence>
        <xsd:element ref="a"/>
        <xsd:element ref="b"/>
      </xsd:sequence>
        <xsd:element ref="a"/>
        <xsd:element ref="b"/>
    </xsd:choice>
   </xsd:complexType>
  </xsd:element>

I kept getting a Unique Particle Attribution rule error for 'a' in 
Stylus Studio. I found a post somewhere that said that this was a bug, 
and when I used Sax, it validated just fine.

If you have a better way of doing it, I'd love to see it. Thanks so 
much for your help, guys.


On Wed, 10 Oct 2007 14:17:28 +0100
  "Michael Kay" <mike@s...> wrote:
> George, your reading of the requirement is very literal.
> 
> "I have a and b, at least one of them has to appear once AND ONLY 
>ONCE." 
> 
> My guess at the likely meaning is to accept a|b|ab. But I might be 
>wrong.
> 
> Michael Kay 
> http://www.saxonica.com/
> 
>> -----Original Message-----
>> From: xmlschema-dev-request@w... 
>> [mailto:xmlschema-dev-request@w...] On Behalf Of George 
>> Cristian Bina
>> Sent: 10 October 2007 08:42
>> To: vwiswell@v...
>> Cc: xmlschema-dev@w...
>> Subject: Re: optional, but at least one required
>> 
>> 
>> Hi Virginia,
>> 
>> I understand that what you want is
>> ab* | a*b
>> and you need to write that in a non ambiguous way to be able 
>> to write it in XML Schema.
>> 
>> So what we need to accept is
>> 
>> a ab abb abbb ...
>> b ab aab aaab ...
>> 
>> 
>> You can write that as
>> 
>> ((a, (b* | (a+, b))) | b)
>> 
>> Best Regards,
>> George
>> ---------------------------------------------------------------------
>> George Cristian Bina - http://aboutxml.blogspot.com/ 
>> <oXygen/> XML Editor, Schema Editor and XSLT Editor/Debugger 
>> www.---.com
>> 
>> 
>> Virginia Wiswell wrote:
>> > I have a similar situation that I'm having trouble with. I 
>> have a and 
>> > b, at least one of them has to appear once AND ONLY ONCE. a 
>> must come before b.
>> > The examples in this thread allow more than one occurrence 
>> of a or b.
>> > 
>> > This is my first attempt at customizing a schema and I'm stuck.
>> > 
>> > TIA, Virginia
>> > 
>> >> You need to specify the requirements in a little more detail:
>> >>
>> >> * are multiple occurrences of a, b, and c allowed?
>> >>
>> >> * what constraints do you want to impose on the ordering 
>> of the elements?
>> >>
>> >> Michael Kay
>> >> http://www.saxonica.com/
>> > 
>> > 
>> > 
>> > 
>> 
> 
> 


From petexmldev@t... Wed Oct 10 18:23:18 2007
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