Create an XML document with multiple namespaces

[mookie]

I want to create the following XML document

<?xml version="1.0" encoding="utf-8" ?>
<root xmlns="

http://www.usa.gov"

xmlns:minn="

http://www.minn.gov">

<Author>
<Name>Joe Johnson</Name>
<minn:Age>47</minn:Age>
</Author>
</root>

The closest I have got is
<?xml version="1.0" encoding="utf-8" ?>
<root xmlns="

http://www.usa.gov"

xmlns:minn="

http://www.minn.gov">

<Author>
<Name>Joe Johnson</Name>
<minn:Age xmlns:minn="

http://www.min.gov">47</minn:Age>

</Author>
</root>

I am using the following code

[WebMethod]
public XmlDocument HelloWorld()
{
XmlDocument xmlDoc = new XmlDocument();
xmlDoc.LoadXml("<root/>");

XmlElement node = xmlDoc.CreateElement("Author");
xmlDoc.DocumentElement.AppendChild(node);

XmlAttribute attr = xmlDoc.CreateAttribute("xmlns");
attr.Value = "

http://www.usa.gov";

xmlDoc.DocumentElement.Attributes.Append(attr);

attr = xmlDoc.CreateAttribute ("xmlns:minn");
attr.Value = "

http://www.minn.gov";

xmlDoc.DocumentElement.Attributes.Append(attr);

XmlElement child1 = xmlDoc.CreateElement("Name");
child1.InnerText = "Joe Johnson";
node.AppendChild(child1);

XmlElement child2 = xmlDoc.CreateElement("minn:Age"); // Causes error
/**** I MUST USE THE LINE BELOW FOR THE CODE TO WORK */
//XmlElement child2 = xmlDoc.CreateElement("minn:Age", "

http://www.min.gov");

child2.InnerText = "47";
node.AppendChild(child2);

return xmlDoc;
}


With the code above I get the error " Cannot use a prefix with an empty namespace."


I am not a XML expert, so I might mis-understand the concept. If I define a namespace at the top of the document and specify a prefix for that namespace and I use the prefix on an element below, why would I need a namespace defined for the element.

Any help would be greatly appreciated, thanks