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Hi,
The clause 47.7.1 of X.680 says
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The "PermittedAlphabet" notation shall be
PermittedAlphabet ::= FROM
Constraint.
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The clause 47.7.3 of X.680 specifies
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The "Constraint" is any which could
be applied to the parent type (Table 9), except that it shall
use
the "SubtypeConstraint" alternative of
"ConstraintSpec".
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So, the following forms of permitted alphabet constraints
are all
valid according to 47.7.3:
1)DummyString1 ::= IA5String (FROM("A".."B"))
-- value range form
2)DummyString2 ::= IA5String
(FROM("A")) -- single value form
3)DummyString3 ::= IA5String (FROM(INCLUDES
DummyStringType))
-- contained type form
DummyStringType ::= IA5String
(FROM("abcd"))(SIZE(4))
4)DummyString4 ::= IA5String (FROM(SIZE(4))) -- size
constraint form
5)DummyString5 ::= IA5String (FROM(PATTERN
"[a-z]+"))
However, as this subtype element implies, permitted
alphabet selects the charaters
which are allowed to be used to construct strings of the new
constrained type. So,
I think that only 1) and 2) make sense. 3),4) and
5) are equivalent to the contraints
within the PermittedAlphabet notation.
For example, 4) is equivalent to the notation
DummyString4 ::= IA5String(SIZE(4)).
So, my question is why not change
the clause 47.7.3 of X.680 into the
following statement:
"The 'contraint' is only
limited to the single value, the contained subtype and the value
range
or set arithmetic of them"
?
Author Name: Wang
Hao
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