[Mpi-forum] Reserved MPI_ prefix & namespace in C and Fortran

N.M. Maclaren nmm1 at cam.ac.uk
Sun Aug 26 11:47:31 CDT 2012

On Aug 26 2012, Rolf Rabenseifner wrote:
>About 1.: Yes, agreed. Always must and should are used as
>synonyms in the scope of standards. To use the same
>words in both sentences is clarifying that there is
>no relevant difference in the meaning.

Sorry, but definitely not in ISO standards!  From ISO
Directives Part 2:

Table H.1 - Requirement
Verbal form       Equivalent expressions
shall             is to
                  is required to
                  it is required that
                  has to
                  only ... is permitted
                  it is necessary
shall not         is not allowed [permitted] [acceptable] [permissible]
                  is required to be not
                  is required that ... be not
                  is not to be

Do not use "must" as an alternative for "shall". (This will avoid any
confusion between the requirements of a document and external statutory
obligations.)  Do not use "may not" instead of "shall not" to express a

Table H.2 - Recommendation
Verbal form        Equivalent expressions
should             it is recommended that
                   ought to
should not         it is not recommended that
                   ought not to

[End of extract]

However, in non-ISO standards (and fairly often even in them!, "must"
is used as a synonym for "shall".  It is definitely never a synonym
for "should".

Nick Maclaren.

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