code: public boolean existsElement(String predicate) throws org.odmg.QueryInvalidException
      {
          DList results = (DList) this.query(predicate);
          if (results == null || results.size() == 0)
              return false;
          else
              return true;
      }
docs: Determines whether there is an element of the collection that evaluates to true
  for the predicate.
  @param	predicate	An OQL boolean query predicate.
  @return	True if there is an element of the collection that evaluates to true
  for the predicate, otherwise false.
  @exception	org.odmg.QueryInvalidException	The query predicate is invalid.