How to allow upgrade with Wix.

Wix Toolset Upgrade

<?xml version="1.0" encoding="UTF-8"?>
<?define ProductVersion="!(bind.FileVersion.MyAssemblyDll)"?>
<?define UpgradeCode="f4d7f199-28f6-45d5-ad99-7c62938274be"?>
<?define ProductId="{6408D956-40DA-4AEE-883E-5425F1562004}"?>
<?define Version="1.0.0"?>


<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi">
	<Product Id="*" Name="UpgradeTest" Language="1033" Version="$(var.Version)" Manufacturer="xxx" UpgradeCode="$(var.UpgradeCode)">
		<Package Id="*" InstallerVersion="200" Compressed="yes" InstallScope="perMachine" /> 
    
    <Upgrade Id ="$(var.UpgradeCode)">
      <UpgradeVersion Minimum="$(var.Version)" OnlyDetect="yes" Property="NEWERVERSIONDETECTED"/>
      <UpgradeVersion Maximum="$(var.Version)" IncludeMaximum="no" Property="OLDERVERSIONBEINGUPGRADED"/>      
    </Upgrade>

    <InstallExecuteSequence>
      <RemoveExistingProducts After="InstallValidate"/>
    </InstallExecuteSequence>

    <Condition Message="A newer version of [ProductName] is already installed. If you are sure you want to downgrade, remove the existing installation via Programs and Features.">Not NEWERVERSIONDETECTED</Condition>
    
		<MediaTemplate EmbedCab="yes"/>

		<Feature Id="ProductFeature" Title="UpgradeTest" Level="1">
			<ComponentGroupRef Id="ProductComponents" />
		</Feature>
	</Product>

	<Fragment>
		<Directory Id="TARGETDIR" Name="SourceDir">
			<Directory Id="ProgramFilesFolder">
				<Directory Id="INSTALLFOLDER" Name="UpgradeTest" />
			</Directory>
		</Directory>
	</Fragment>

	<Fragment>
		<ComponentGroup Id="ProductComponents" Directory="INSTALLFOLDER">
			<!-- TODO: Remove the comments around this Component element and the ComponentRef below in order to add resources to this installer. -->
			 <Component Id="ProductComponent">
         <File Id="Productwxs" Source="Product.wxs" KeyPath="yes" />
			 </Component> 
		</ComponentGroup>
	</Fragment>
</Wix>

Quick question: what is the defined ProductId and ProductVersion used for? I don't see them coming up anymore?