The version 0.5.2 of the simple parameter plugin allows to return other types than a string (e.g. a date or a boolean) in outputs. The 'support typed outputs' option must be checked for this purpose. The column title must include the type name at the end of the column name, preceded by an underscore character (e.g. 'column_name_flag' for a boolean output). See the attached screenshots for examples. Note that the input remains a string type. It means that if the search key is based on the 'column_name_flag' column, the input must be the "true" string for an output showing the 'true' boolean.