How to get an typed value for xml

I have an XmlAttribute defined in xsd file as a short. After I create an
XmlDocument and add an element to it, I create an attribute for the element
and I set the value of the attribute as "3". However, the TypedValue in the
last line of the following code does not give me a short value. Instead, it
is still a string value of "3". Why? How do I get a typed value from an
xml/xsd pair?

// create an XmlDocument here and add header part of an xml here

XmlSchemaSet mySet = new XmlSchemaSet();
XmlSchema schema = mySet.Add(null, "c:\\mySchema.xsd");
mySet.Compile();
myDoc.Schema = mySet;
ValidationEventHandler handler = new ValidationEventHandler(myHandler);
myDoc.Validate(handler);
XPathNavigator navigator = attribute.CreateNavigator();
short value = (short)navigator.TypedValue;