Hi Peter,

The following schema will do it.
The model is:
(
  (aa, ((bb, (cc | dd)*) | ((cc | dd)+, bb, (cc | dd)*))) |
  (bb, ((aa, (cc | dd)*) | ((cc | dd)+, aa, (cc | dd)*))) |
  (
   (cc | dd)+,
   (
    (aa, ((bb, (cc | dd)*) | ((cc | dd)+, bb, (cc | dd)*))) |
    (bb, ((aa, (cc | dd)*) | ((cc | dd)+, aa, (cc | dd)*)))
   )
  )
)


<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
     <xsd:element name="element">
         <xsd:complexType>
             <xsd:choice>
                 <xsd:sequence>
                     <xsd:element ref="aa"/>
                         <xsd:choice>
                             <xsd:sequence>
                                 <xsd:element ref="bb"/>
                                 <xsd:choice minOccurs="0" 
maxOccurs="unbounded">
                                     <xsd:element ref="cc"/>
                                     <xsd:element ref="dd"/>
                                 </xsd:choice>
                             </xsd:sequence>
                             <xsd:sequence>
                                 <xsd:choice minOccurs="1" 
maxOccurs="unbounded">
                                     <xsd:element ref="cc"/>
                                     <xsd:element ref="dd"/>
                                 </xsd:choice>
                                 <xsd:element ref="bb"/>
                                 <xsd:choice minOccurs="0" 
maxOccurs="unbounded">
                                     <xsd:element ref="cc"/>
                                     <xsd:element ref="dd"/>
                                 </xsd:choice>
                             </xsd:sequence>
                         </xsd:choice>
                 </xsd:sequence>
                 <xsd:sequence>
                     <xsd:element ref="bb"/>
                     <xsd:choice>
                         <xsd:sequence>
                             <xsd:element ref="aa"/>
                             <xsd:choice minOccurs="0" 
maxOccurs="unbounded">
                                 <xsd:element ref="cc"/>
                                 <xsd:element ref="dd"/>
                             </xsd:choice>
                         </xsd:sequence>
                         <xsd:sequence>
                             <xsd:choice minOccurs="1" 
maxOccurs="unbounded">
                                 <xsd:element ref="cc"/>
                                 <xsd:element ref="dd"/>
                             </xsd:choice>
                             <xsd:element ref="aa"/>
                             <xsd:choice minOccurs="0" 
maxOccurs="unbounded">
                                 <xsd:element ref="cc"/>
                                 <xsd:element ref="dd"/>
                             </xsd:choice>
                         </xsd:sequence>
                     </xsd:choice>
                 </xsd:sequence>
                 <xsd:sequence>
                     <xsd:choice minOccurs="1" maxOccurs="unbounded">
                         <xsd:element ref="cc"/>
                         <xsd:element ref="dd"/>
                     </xsd:choice>
                     <xsd:choice>
                         <xsd:sequence>
                             <xsd:element ref="aa"/>
                             <xsd:choice>
                             <xsd:sequence>
                                 <xsd:element ref="bb"/>
                                 <xsd:choice minOccurs="0" 
maxOccurs="unbounded">
                                     <xsd:element ref="cc"/>
                                     <xsd:element ref="dd"/>
                                 </xsd:choice>
                             </xsd:sequence>
                             <xsd:sequence>
                                 <xsd:choice minOccurs="1" 
maxOccurs="unbounded">
                                     <xsd:element ref="cc"/>
                                     <xsd:element ref="dd"/>
                                 </xsd:choice>
                                 <xsd:element ref="bb"/>
                                 <xsd:choice minOccurs="0" 
maxOccurs="unbounded">
                                     <xsd:element ref="cc"/>
                                     <xsd:element ref="dd"/>
                                 </xsd:choice>
                             </xsd:sequence>
                         </xsd:choice>
                         </xsd:sequence>
                         <xsd:sequence>
                             <xsd:element ref="bb"/>
                             <xsd:choice>
                             <xsd:sequence>
                                 <xsd:element ref="aa"/>
                                 <xsd:choice minOccurs="0" 
maxOccurs="unbounded">
                                     <xsd:element ref="cc"/>
                                     <xsd:element ref="dd"/>
                                 </xsd:choice>
                             </xsd:sequence>
                             <xsd:sequence>
                                 <xsd:choice minOccurs="1" 
maxOccurs="unbounded">
                                     <xsd:element ref="cc"/>
                                     <xsd:element ref="dd"/>
                                 </xsd:choice>
                                 <xsd:element ref="aa"/>
                                 <xsd:choice minOccurs="0" 
maxOccurs="unbounded">
                                     <xsd:element ref="cc"/>
                                     <xsd:element ref="dd"/>
                                 </xsd:choice>
                             </xsd:sequence>
                         </xsd:choice>
                         </xsd:sequence>
                     </xsd:choice>
                 </xsd:sequence>
             </xsd:choice>
         </xsd:complexType>
     </xsd:element>
     <xsd:element name="aa"/>
     <xsd:element name="bb"/>
     <xsd:element name="cc"/>
     <xsd:element name="dd"/>
</xsd:schema>


Hope that helps,
George
-----------------------------------------------
George Cristian Bina
<oXygen/> XML Editor & XSLT Editor/Debugger
www.---.com


Peter Menzel wrote:
> 
> Hi all,
> 
> i am working on a xml schema and have the following problem, maybe 
> somebody can help me.
> 
> I would like to have the follwoing element with content:
> 
> <element>
>   <aa/>
>   <cc/>
>   <bb/>
> </element>
> 
> The elements aa and bb are required to be there and they have to occur 
> exactly once.
> Other sub elements of element can occur many times. Especially the order 
> of the elements is random, so i may not use xsd:sequence.
> 
> My xml schema snippet for this element:
> 
> <xsd:element name='element'>
>  <xsd:complexType>
>      <xsd:choice>
>           <xsd:element ref='dd' minOccurs='0' maxOccurs='unbounded'/>
>           <xsd:element ref='cc' minOccurs='0' maxOccurs='unbounded'/>
>           <xsd:element ref='aa' minOccurs='1' maxOccurs="1"/>
>           <xsd:element ref='bb' minOccurs='1' maxOccurs="1"/>
>       </xsd:choice>
>   </xsd:complexType>
> </xsd:element>
> 
> Unfortunately this wont work.
> xmllint says that the above xml document is not valid with this schema.
> 
> Has anybody any idea concerning this problem? Is it generally possible 
> to mix elements in a complexType  with different minOccurs/maxOccurs ?
> 
> Greetings, Peter
> 

From jeni@jeni