suggestions for strange schema

[anonymous]

I need a bit of help defining a schema to validate some xml. I can't figure out how to get it to work; I believe I need the combined functionality of something like these two type definitions. Some sample xml is below. There is a comment node that describes the possible variations in the document.

<xs:complexType name="DataType">
<xs:all minOccurs="0">
<xs:element name="singleInstanceElement1" minOccurs="0"/>
<xs:element name="singleInstanceElement1" minOccurs="0"/>
</xs:all>
</xs:complexType>

<xs:complexType name="DataType">
<xs:choice minOccurs="0" maxOccurs="unbounded">
<xs:element name="repeatableElement1" minOccurs="0"/>
<xs:element name="repeatableElement2" minOccurs="0"/>
</xs:choice>
</xs:complexType>


<?xml version="1.0" encoding="utf-8"?>
<!--
elements within data are not ordered
single instance elements may appear 0 or 1 time within data
repeatable elements may appear an arbitrary number of times
-->
<data>
<singleInstanceElement1></singleInstanceElement1>
<repeatableElement1></repeatableElement1>
<repeatableElement2></repeatableElement2>
<singleInstanceElement2></singleInstanceElement2>
<repeatableElement1></repeatableElement1>
</data>