public function addString($str_name, $bol_index = TRUE)
    {
        return $this->addProperty($str_name, self::PROPERTY_STRING, $bol_index);
    }
public function addString($str_name, $bol_index = TRUE)
    {
        return $this->addProperty($str_name, self::PROPERTY_STRING, $bol_index);
    }
public function addString ( $ str_name , $ bol_index = TRUE ) { return $ this -> addProperty ( $ str_name , self :: PROPERTY_STRING , $ bol_index ) ; }
Add a string field to the schema

@param $str_name
@param bool $bol_index
@return Schema
Add a string field to the schema