WPF

IsLoading = true;
//sim a delay
Thread.Sleep(TimeSpan.FromSeconds(0.75).Milliseconds);

UI.UIDispatcher.Invoke((ThreadStart)delegate()
    {
        foreach (Unit u in UnitCache.Units.AllUnits.Where(WhereClause))
        base.Children.Add(new UnitTreeItemViewModel(u, this, _uh));
    });

IsLoading = false;

<TextBlock Text="..."
           x:Name="loadingText"
           Visibility="{Binding Path=IsLoading, Converter={StaticResource BooleanToVisibilityConverter}}"/>

If I have an xml document of books, like:

<Books>
  <Book>
    <Title>WPF For The Hard-of-Learning</Title>
    <Category>N</Category>
  </Book>
</Books>

and an xml document of book categories:

<Categories>
  <Category>
    <ID>F</ID>
    <Name>Fiction</Name>
  </Category>
  <Category>
    <ID>N</ID>
    <Name>Non-Fiction</Name>
  </Category>
</Categories>

is there a way to bind the element value from the second document that is associated with an element in the first document?

To clarify using the above xml document examples, I'd like to display the book title and its category name (Non-Fiction), not its Category code (N).

In a code-behind file I'd like to load into XmlDocument objects the xml from a file that holds the Books xml and from a file that holds the Categories xml. In the code-behind I would assign the xml documents as the Document property of a couple XmlDataProviders defined in the XAML.