Problem with xml schema elements hierarchy

Question

What's wrong with this xml schema? It doesn't parse correctly, and I can't realize a hierarchy between cluster(element)->host(element)->Load(element).

<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"&gt;

  <xs:element name="cluster">
    <xs:complexType>
      <xs:sequence>
        <xs:element ref="host"/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>

  <xs:element name="host">
    <xs:complexType>
      <xs:element ref="Load"/>
      <xs:attribute name="name" type="xs:string" use="required"/>
    </xs:complexType>
  </xs:element>

  <xs:element name="Load">
    <xs:complexType>
      <xs:attribute name="usedPhisicalMemory" type="xs:integer"/>
    </xs:complexType>
  </xs:element>

</xs:schema>

Thank you, Emilio

Answer 1

In the host element, the load element cannot be a child of complexType, you must have a sequence, etc. in between.

Answer 2

To allow something like this (I corrected the typo in "usedPhysicalMemory"):

<cluster>
  <host name="foo">
    <Load usedPhysicalMemory="500" />
  </host>
  <host name="bar">
    <Load usedPhysicalMemory="500" />
  </host>
</cluster>

This schema would do it:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"&gt;

  <xs:element name="cluster">
    <xs:complexType>
      <xs:sequence>
        <xs:element ref="host" maxOccurs="unbounded" />
      </xs:sequence>
    </xs:complexType>
  </xs:element>

  <xs:element name="host">    
    <xs:complexType>
      <xs:sequence>
        <xs:element ref="Load" />
      </xs:sequence>
      <xs:attribute name="name" type="xs:string" use="required" />
    </xs:complexType>
  </xs:element>

  <xs:element name="Load">
    <xs:complexType>
      <xs:attribute name="usedPhysicalMemory" type="xs:integer" />
    </xs:complexType>
  </xs:element>    

</xs:schema>

From the MSDN on <xs:complexType> (because the spec makes my brain hurt):

If group, sequence, choice, or all is specified, the elements must appear in the following order:

1. group | sequence | choice | all
2. attribute | attributeGroup
3. anyAttribute

Maybe someone else can point out the relevant section in the spec.