Paul, I didn't mean to trivialize the power of the whole facility. Rather, I am just interested in the encoding of this one isolated construct.
Paul Long ipDialog, Inc. > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Paul > Thorpe > Sent: Monday, June 24, 2002 6:42 PM > To: [EMAIL PROTECTED] > Subject: RE: [ASN.1] TYPE-IDENTIFIER.&Type > > > Hi Paul, > > I will answer your second question. No, that is not all there is to > it. The real benefit of the all of this "&." comes from using table > constraints (and component relation constraints) rather than just a type > constraint as shown in your example. I suggest you refer the book > "Communications Between Heterogenus Systems" by Oliver Dubuisson, or > "ASN.1 Complete" by John Larmouth for good explanations of the real power > of this notation. Both of these books are downloadable free of charge > from www.oss.com, or can be purchased from amazon.com. > > ------------------------------------------------------------------ > ---------- > Paul E. Thorpe Toll Free : > 1-888-OSS-ASN1 > OSS Nokalva International: > 1-732-302-0750 > Email: [EMAIL PROTECTED] Tech Support : > 1-732-302-9669 > http://www.oss.com Fax : > 1-732-302-0023 > > On Mon, 24 Jun 2002, Paul Long wrote: > > > Rajul, > > > > Okay, thanks. So I think you're answer to my first question is, yes. :-) > > > > Also, given X: > > > > X ::= SEQUENCE { > > a INTEGER, -- stuff... > > b BOOLEAN > > } > > > > I believe that Z1: > > > > Z1 ::= SEQUENCE { > > y TYPE-IDENTIFIER.&Type (X) > > } > > > > encodes in PER exactly like Z2: > > > > Z2 ::= SEQUENCE { > > y OCTET STRING -- contains X > > } > > > > True? > > > > Paul Long > > ipDialog, Inc. > > > > > -----Original Message----- > > > From: Rajul Gupta [mailto:[EMAIL PROTECTED]] > > > Sent: Monday, June 24, 2002 4:13 PM > > > To: [EMAIL PROTECTED] > > > Cc: [EMAIL PROTECTED] > > > Subject: Re: [ASN.1] TYPE-IDENTIFIER.&Type > > > > > > > > > Hi Paul, > > > > > > (X) is a type constraints here, and it says that "y" MUST be > of type "X" > > > only. Syntactically, this is equivalent to > > > > > > Z ::= SEQUENCE { > > > y X > > > } > > > > > > However, this kind of syntax (your syntax) is useful in case > of PER. PER > > > always doesn't have length encoded, but while encoding open > > > types, PER puts > > > a length wrapper also. So if you are using PER, then at the > decoding side > > > you can easily find out the length of encoded open type value, without > > > knowing it's type. > > > > > > Usually this type of construct is useful for security fields. > Using length > > > wrapper you can easily find out the length of security data > and leave this > > > data unwrapped and unprocessed in your application, and pass > it to other > > > application or function, where this security data is used. > > > > > > I hope this answer could be helpful for you. > > > > > > Rajul > > > > > > > I've put it off too long. Now it's time for me learn this > ".&" stuff. Is > > > y, > > > > below, encoded in PER as an open type that contains an > encoding of X? Is > > > > that all there is to it? > > > > Also, what syntactical role does the "(X)" play? Is > > > > this a constraint and otherwise y could be encoded as an open > > > type of any > > > > type? > > > > X ::= SEQUENCE { > > > > a INTEGER, -- stuff... > > > > b BOOLEAN > > > > } > > > > > > > > Z ::= SEQUENCE { > > > > y TYPE-IDENTIFIER.&Type (X) > > > > } > > > > > > > > Paul Long > > > > ipDialog, Inc.
