/**
  * check if the index should be visible
  *
  * @return
  */
 @Override
 public boolean isVisible() {
   if (sourceIndex != null) {
     if (getDomain().isDynamic()) {
       return sourceIndex.isVisible();
     } else {
       return !source.getDimension().isDynamic()
           && sourceIndex.isVisible(); // if explicit link and the target is visible
     }
   } else {
     return false;
   }
 }