Re: [ASN1] a quesion on Permitted Alphabet constraint

[Salim Alaoui]

>>For example, 4) is equivalent to the notation DummyString4 ::= IA5String(SIZE(4)).

FROM(SIZE(4)) in my opinion is that the maximum size is 4 which is not quite equivalent to (SIZE(4)) where the size has to be exactly 4.

 

-Cheers-

 

Salim Mounir Alaoui, Ph.D.

WangHao <[EMAIL PROTECTED]> wrote:

Hi,

 

The clause 47.7.1 of X.680 says

_________________________________________________________________________________

The "PermittedAlphabet" notation shall be

     PermittedAlphabet ::= FROM Constraint.

________________________________________________________________________________

 

The clause 47.7.3 of X.680 specifies

________________________________________________________________________________

The "Constraint" is any which could

be applied to the parent type (Table 9), except that it shall use

the "SubtypeConstraint" alternative of "ConstraintSpec".

________________________________________________________________________________

 

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
Phone:+86-755-89650628
EMail:[EMAIL PROTECTED]
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