WPF

<Window x:Class="WpfApplication4.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
		<Rectangle Height="18">
			<Rectangle.Fill>
				<LinearGradientBrush StartPoint="0.5,0" EndPoint="0.5,1">
					<GradientStop Offset="0" Color="Red" />
					<GradientStop Offset="0.611111111111111" Color="Red" />
					<GradientStop Offset="0.611111111111111" Color="Green" />
					<GradientStop Offset="1" Color="Green" />
				</LinearGradientBrush>
			</Rectangle.Fill>
		</Rectangle>
	</Grid>
</Window>

using System.Collections.ObjectModel;
using System.ComponentModel;
//using ChurchWX.Classes;

namespace ChurchWX
{
    public class ViewModel : INotifyPropertyChanged
    {
        private ObservableCollection<Group> _groups;
        public ObservableCollection<Group> Groups
        {
            get { return _groups; }
            set
            {
                _groups = value;
                OnPropertyChanged("Groups");
            }
        }

        public ViewModel()
        {
            Groups = GenerateGroups();
        }

        private ObservableCollection<Group> GenerateGroups()
        {
            ObservableCollection<Group> groups = new ObservableCollection<Group>();

            //create the mail group with menu items
            var mailGroup = new Group() { Title = "Mail",
                LargeImagePath = @"/XamOutlookBarDataBinding;component/Images/Mail32.png", 
                SmallImagePath = @"/XamOutlookBarDataBinding;component/Images/Mail16.png" };
            var rootMailItem = new MenuItem() { Title = "Personal Folders", IsExpanded = true };
            rootMailItem.Children.Add(new MenuItem() { Title = "Inbox", ImagePath = @"/XamOutlookBarDataBinding;component/Images/InboxFolder16.png" });
            rootMailItem.Children.Add(new MenuItem() { Title = "Drafts", ImagePath = @"/XamOutlookBarDataBinding;component/Images/DraftsFolder16.png" });
            rootMailItem.Children.Add(new MenuItem() { Title = "Sent Items", ImagePath = @"/XamOutlookBarDataBinding;component/Images/SentFolder16.png" });
            rootMailItem.Children.Add(new MenuItem() { Title = "Deleted Items", ImagePath = @"/XamOutlookBarDataBinding;component/Images/DeletedFolder16.png" });
            mailGroup.Items.Add(rootMailItem);

            //create the contacts group with menu items
            var contactsGroup = new Group() { Title = "Contacts", 
                LargeImagePath = @"/XamOutlookBarDataBinding;component/Images/Contact32.png", 
                SmallImagePath = @"/XamOutlookBarDataBinding;component/Images/Contact16.png" };
            var rootContactItem = new MenuItem() { Title = "My Contacts", IsExpanded = true };
            rootContactItem.Children.Add(new MenuItem() { Title = "Suggested Contacts", ImagePath = @"/XamOutlookBarDataBinding;component/Images/Contact16.png" });
            rootContactItem.Children.Add(new MenuItem() { Title = "Contacts" , ImagePath = @"/XamOutlookBarDataBinding;component/Images/Contact16.png" });
            contactsGroup.Items.Add(rootContactItem);

            groups.Add(mailGroup);
            groups.Add(contactsGroup);

            return groups;
        }

        public event PropertyChangedEventHandler PropertyChanged;
        protected void OnPropertyChanged(string propertyname)
        {
            var handler = PropertyChanged;
            if (handler != null)
                handler(this, new PropertyChangedEventArgs(propertyname));
        }
    }
}

<UserControl xmlns:toolkit="http://schemas.microsoft.com/winfx/2006/xaml/presentation/toolkit"  x:Class="ChurchWX.MainPage"
    xmlns:local="clr-namespace:ChurchWX"
    xmlns:D="clr-namespace:ChurchWX.Classes"
    xmlns:ig="http://schemas.infragistics.com/xaml" 
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
    xmlns:sdk="http://schemas.microsoft.com/winfx/2006/xaml/presentation/sdk">

    <UserControl.DataContext>
        <local:ViewModel/>
    </UserControl.DataContext>
    
        
    
    <UserControl.Resources>
        <Style TargetType="ig:OutlookBarGroup">   
            <Setter Property="Header" Value="{Binding Title}"/>
            <Setter Property="LargeIconTemplate"  Value="{Binding LargeImagePath}"/>
            <Setter Property="SmallIconTemplate" Value="{Binding SmallImagePath}"/>
            <Setter Property="Content" Value="{Binding Items}" />
            <Setter Property="ContentTemplate">
                <Setter.Value>
                    <DataTemplate >
                        <ig:XamDataTree ItemsSource="{Binding}">
                            <ig:XamDataTree.GlobalNodeLayouts>
                                <ig:NodeLayout Key="ItemsLayout" TargetTypeName="MenuItem" DisplayMemberPath="Title" IsExpandedMemberPath="IsExpanded">
                                    <ig:NodeLayout.CollapsedIconTemplate>
                                        <DataTemplate>
                                            <Image Source="{Binding Data.ImagePath}" />
                                        </DataTemplate>
                                    </ig:NodeLayout.CollapsedIconTemplate>
                                </ig:NodeLayout>
                            </ig:XamDataTree.GlobalNodeLayouts>                            
                        </ig:XamDataTree>
                    </DataTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </UserControl.Resources>

    <Grid x:Name="LayoutRoot" Background="White">
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
        <Border x:Name="brTop" Grid.Row="0" BorderBrush="White" BorderThickness="0,0,0,1" Height="30">
            <Border.Background>
                <LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
                    <GradientStop Color="White" Offset="0.299"/>
                    <GradientStop Color="#FFC1C9CD" Offset="0.979"/>
                </LinearGradientBrush>
            </Border.Background>
            <TextBlock Margin="12,0,0,0" Text="Church Works v1.0.0" FontSize="12" 
				VerticalAlignment="Center" HorizontalAlignment="Left" FontWeight="Bold">
				<TextBlock.Effect>
					<DropShadowEffect Color="White" BlurRadius="1" ShadowDepth="1"/>
				</TextBlock.Effect>
				<TextBlock.Foreground>
					<LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
						<GradientStop Color="#FFB292DA"/>
						<GradientStop Color="#FF292929" Offset="1"/>
					</LinearGradientBrush>
				</TextBlock.Foreground>
            </TextBlock>
        </Border>
        <Grid x:Name="MainPageLayoutRoot" Grid.Row="1">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="Auto"  MinWidth="60" />
                <ColumnDefinition Width="4"/>
                <ColumnDefinition Width="*"/>
            </Grid.ColumnDefinitions>
            <Canvas x:Name="propertyCanvas" Grid.Column="2"></Canvas>
            <StackPanel Name="stpOutlookBar" Grid.Row="0" Orientation="Horizontal" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Width="150">
                <ig:XamOutlookBar GroupsSource="{Binding Groups}"/>
            </StackPanel>
            <sdk:GridSplitter Grid.Column="1" HorizontalAlignment="Left" Grid.RowSpan="2" Background="#FFBACBFF"/>
            <StackPanel Grid.Column="2" Width="800">                
                <Grid x:Name="WorkAreaLayoutRoot" Background="White" Grid.Column="2">
                    
                </Grid>
            </StackPanel>
            
        </Grid>

        
    </Grid>


</UserControl>

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.