public static Uri GetRelativeUri(Uri sourcePartUri, Uri targetPartUri)
{
Check.SourcePartUri(sourcePartUri);
Check.TargetPartUri(targetPartUri);
Uri uri = new Uri("http://fake.com");
Uri a = new Uri(uri, sourcePartUri.OriginalString);
Uri b = new Uri(uri, targetPartUri.OriginalString);
return a.MakeRelativeUri(b);
}