<Bundle>
 <Variable Name="PASSED_DATABASE" Type="string"  bal:Overridable="yes" Value="DefaultDatabase" />
    <Chain>
      <PackageGroupRef Id="myApp.Database"></PackageGroupRef>
      <PackageGroupRef Id="myApp.Service"></PackageGroupRef>
      <PackageGroupRef Id="myApp.ApplicationName"></PackageGroupRef>
    </Chain>
  </Bundle>

<PackageGroup Id="myApp.Database">
  <MsiPackage
    Id="myApp.Database"
    DisplayName="myApp - Database"
    DisplayInternalUI="yes"
    Visible="yes"
    EnableFeatureSelection="yes"
    SourceFile="$(var.myAppDB.Installer.TargetDir)myAPPDB.msi">
    <MsiProperty Name="PASSED_DATABASE" Value="[PASSED_DATABASE]"/>
  </MsiPackage>
</PackageGroup>