Positional parameters follow the command name in a prescribed sequence. There are two types of positional parameters: required and optional. You must specify required positional parameters immediately after the command name. If you use optional positional parameters, you must specify them immediately after any required positional parameters. If the command does not have any required positional parameters, you must specify any optional positional parameters immediately after the command name. If you specify a list of items to replace a positional parameter, you must put parentheses around the list; otherwise, you do not have to use the parentheses. For example, you can specify a list of data set names with the ALTERDS command by putting parentheses around the list of data set names. If you specify only one data set name, you do not have to use parentheses.