Converting a one-to-many xml design to a many-to-many

I have an xml file format that looks something like this:

<topLevelTag>
  <category name="foo">
    <item attrib="value">ItemName</item>
    <item attrib="value2">AnotherItem</item>
  </category>
  <category name="bar">
    <item attrib="value">ItemName</item>
    <item attrib="value2">AnotherItem</item>
  </category>
</topLevelTag>

The code that parses this creates an instance of ItemName and is told that it's one category is, in the first case, "foo", and then creates a second instance of ItemName which has associated category "bar".

The problem is that I need to redesign the system so that each Item can have more than one Category. But I still need to be able to create multiple items as well. For example (using bullets instead of xml) I might need to create the following instances:

• ItemName
  
  
  
  • Primary Category - "foo"
  
  
  • Secondary Category - "bar"
  
  
  
  


• ItemName
  
  
  
  • Primary Category - "bar"
  
  
  • Secondary Category - "foo"
  
  
  
  


• ItemName
  
  
  
  • Primary Category - "foo"
  
  
  • Secondary Category - "quux"
  
  
  
  


• AnotherItem
  
  
  
  • Primary Category - "baz"
  
  
  • Secondary Category - "foo"
  
  
  • Tertiary Category - "monkey"
  
  
  • etc ... (no cap)
  
  
  
  


• StillAnotherItem
  
  
  
  • etc ...
  
  
  
  


• etc ... (no cap)

How can I design my XML format to encapsulate this many-to-many relationship?

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I am aware this question is on the borderline between StackOverflow and Programmers. I chose to put it here because it is a software architecture and design question. If not please let me know and I'll be happy to move it. Precedent one | Precedent two | Precedent three