/** Return any tables that are defined by this expression (and not its base). */
 @Override
 public List<DatabaseTable> getOwnedTables() {
   ClassDescriptor descriptor = getDescriptor();
   List<DatabaseTable> tables = null;
   if (descriptor == null) {
     List additionalTables = getAdditionalTables();
     if (additionalTables == null) {
       return null;
     } else {
       return new ArrayList(additionalTables);
     }
   } else if (descriptor.isAggregateDescriptor()) {
     return null;
   } else if ((descriptor.getHistoryPolicy() != null)
       && (getAsOfClause() != null && getAsOfClause().getValue() != null)) {
     tables = descriptor.getHistoryPolicy().getHistoricalTables();
   } else if (isUsingOuterJoinForMultitableInheritance()) {
     tables = descriptor.getInheritancePolicy().getAllTables();
   } else {
     tables = descriptor.getTables();
   }
   List additionalTables = getAdditionalTables();
   if (additionalTables != null) {
     tables = new Vector(tables);
     Helper.addAllUniqueToList(tables, additionalTables);
     return tables;
   }
   return tables;
 }