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A new piece of syntax is needed in cADL to support this constraint. It takes the form of the following example:
some_duration matches {PWD/|P0W..P50W|}

The production rule added to an ADL parser is as follows:

c_duration_constraint:
          duration_pattern
        | duration_pattern '/' duration_interval_value -- new rule
        | duration_value
        | duration_interval_value
;

where duration_pattern is a rule like the following (this one is from the Eiffel reference ADL parser):

duration_pattern: V_ISO8601_DURATION_CONSTRAINT_PATTERN
                {
                       if valid_iso8601_duration_constraint_pattern ($1) then -- this function performs further validation on the pattern to ensure it is iso8601 compliant
                               create c_duration.make_from_pattern ($1)
                       else
                                raise_error
                                report_error ("invalid duration constraint pattern; legal pattern: P[Y|y][M|m][W|w][D|d][T[H|h][M|m][S|s]] or P[W|w]")
                                abort
                       end
                }
        ;

And the token V_ISO8601_DURATION_CONSTRAINT_PATTERN has a lexer rule like the following:

-- the following includes the openEHR deviation from ISO8601, to allow 'W' to be mixed in with
-- other designators
P[yY]?[mM]?[Ww]?[dD]?T[hH]?[mM]?[sS]? |
P[yY]?[mM]?[Ww]?[dD]? {
                                last_token := V_ISO8601_DURATION_CONSTRAINT_PATTERN
                                last_string_value := text
                   }


In the AOM, the invariant of C_DURATION is relaxed to allow both range and pattern to be set at the same time.

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A new piece of syntax is needed in cADL to support this constraint. It takes the form of the following example: some_duration matches {PWD/|P0W..P50W|} The production rule added to an ADL parser is as follows: c_duration_constraint:           duration_pattern         | duration_pattern '/' duration_interval_value -- new rule         | duration_value         | duration_interval_value ; where duration_pattern is a rule like the following (this one is from the Eiffel reference ADL parser): duration_pattern: V_ISO8601_DURATION_CONSTRAINT_PATTERN                 {                        if valid_iso8601_duration_constraint_pattern ($1) then -- this function performs further validation on the pattern to ensure it is iso8601 compliant                                create c_duration.make_from_pattern ($1)                        else                                 raise_error                                 report_error ("invalid duration constraint pattern; legal pattern: P[Y|y][M|m][W|w][D|d][T[H|h][M|m][S|s]] or P[W|w]")                                 abort                        end                 }         ; And the token V_ISO8601_DURATION_CONSTRAINT_PATTERN has a lexer rule like the following: -- the following includes the openEHR deviation from ISO8601, to allow 'W' to be mixed in with -- other designators P[yY]?[mM]?[Ww]?[dD]?T[hH]?[mM]?[sS]? | P[yY]?[mM]?[Ww]?[dD]? {                                 last_token := V_ISO8601_DURATION_CONSTRAINT_PATTERN                                 last_string_value := text                    } In the AOM, the invariant of C_DURATION is relaxed to allow both range and pattern to be set at the same time.