DBMS_SQL.define_column ---- why ????

As an SQL newbie, why do I need to define columns prior to getting column_value when I can fetch_rows(cur_hdl) ?? Does not column_value get the value at position x at the current cursor position and fetch_rows gets a row for a given cursor and increment cursor position ? So why define_column ?

Example.

• describe defines dbms_sql.define_column(cur_hdl, 1, name, 200); dbms_sql.define_column(cur_hdl, 2, salary);
• execute rows_processed := dbms_sql.execute(cur_hdl);

    LOOP

• fetch a row IF dbms_sql.fetch_rows(cur_hdl) > 0 then
  • fetch columns from the row dbms_sql.column_value(cur_hdl, 1, name); dbms_sql.column_value(cur_hdl, 2, salary);
  • <process data>

          ELSE
            EXIT; 
          END IF;