How can you make a sequence of optional items which must be in order in an XML schema?

Question

What I want to do is create a sequence element in an XML schema such that the contents must be in order, but may not all be present. For example, the schema would be something like this:

<xs:element name="rods" maxOccurs="1" minOccurs="1">
 <xs:complexType>
  <xs:sequence>
   <xs:element name="green" type="xs:positiveInteger" />
   <xs:element name="white" type="xs:positiveInteger" />
   <xs:element name="blue" type="xs:positiveInteger" />
   <xs:element name="yellow" type="xs:positiveInteger" />
   <xs:element name="red" type="xs:positiveInteger" />
   <xs:element name="tan" type="xs:positiveInteger" />
   <xs:element name="gray" type="xs:positiveInteger" />
   <xs:element name="black" type="xs:positiveInteger" />
  </xs:sequence>
 </xs:complexType>
</xs:element>

and would allow XML like this:

<rods>
 <green>142</green>
 <white>34</white>
 <gray>65</gray>
</rods>

MSDN has this to say about it:

The following example shows an element (zooAnimals) that can have zero or more of the following elements, elephant, bear, giraffe, in the sequence element.

<xs:element name="zooAnimals">
      <xs:complexType>
            <xs:sequence minOccurs="0" maxOccurs="unbounded">
               <xs:element name="elephant"/>
               <xs:element name="bear"/>
               <xs:element name="giraffe"/>
            </xs:sequence>
      </xs:complexType>
</xs:element>

W3Schools suggests the same. However, both visual studio and an online validation service don't like what is suggested.

Here is what I have at the moment:

<xs:element name="rods" maxOccurs="1" minOccurs="1">
 <xs:complexType>
  <xs:sequence minOccurs="0" maxOccurs="1">
   <xs:element name="green" type="xs:positiveInteger" />
   <xs:element name="white" type="xs:positiveInteger" />
   <xs:element name="blue" type="xs:positiveInteger" />
   <xs:element name="yellow" type="xs:positiveInteger" />
   <xs:element name="red" type="xs:positiveInteger" />
   <xs:element name="tan" type="xs:positiveInteger" />
   <xs:element name="gray" type="xs:positiveInteger" />
   <xs:element name="black" type="xs:positiveInteger" />
  </xs:sequence>
 </xs:complexType>
</xs:element>

And here's the XML:

<rods>
 <green>142</green>
 <white>34</white>
 <gray>65</gray>
</rods>

Visual Studio 2005 claims that "gray" is invalid, "blue" expected, so clearly it wants all of the children

Thanks,

Eric

Answer 1

<xs:element name="rods">
    <xs:complexType>
        <xs:sequence>
                <xs:element minOccurs="0" name="green" type="xs:positiveInteger" />
                <xs:element minOccurs="0" name="white" type="xs:positiveInteger" />
                <xs:element minOccurs="0" name="blue" type="xs:positiveInteger" />
                <xs:element minOccurs="0" name="yellow" type="xs:positiveInteger" />
                <xs:element minOccurs="0" name="red" type="xs:positiveInteger" />
                <xs:element minOccurs="0" name="tan" type="xs:positiveInteger" />
                <xs:element minOccurs="0" name="gray" type="xs:positiveInteger" />
                <xs:element minOccurs="0" name="black" type="xs:positiveInteger" />
        </xs:sequence>
    </xs:complexType>
</xs:element>