/sys$common/syshlp/helplib.hlb OPEN, Parameters  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 logical-name[:]

    Specifies the logical name and a character string to be assigned
    to the file.

 filespec

    Specifies the name of the file or device being opened for input
    or output. The file type defaults to DAT. The asterisk (*)  and
    the percent sign (%)  wildcard characters are not allowed.

    To create a new, sequential file, specify the /WRITE qualifier.
    See the description of the /WRITE qualifier for more information.