How to define table attribute in the record file

Following code is working on Craft 2:

class My_TableRecord extends BaseRecord {
  public function getTableName() {
    return 'my_table';
  }

  protected function defineAttributes() {
    return [
      'title'         => AttributeType::String,
      'description'   => AttributeType::Mixed
    ];
  }
}

According to this documentation the defineAttributes() is not available in Craft 3. So how can I define table’s attributes in Craft3 to complete following code:

class My_TableRecord extends ActiveRecord
{   public static function tableName()
    {
        return '{{%my_table}}';
    }

  //equivalent function of defineAttributes() of Craft3 will go here

}