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From: tebbutt@RHINO.NCSL.NIST.GOV (John Tebbutt)
Newsgroups: comp.protocols.iso.dev-environ
Subject: OPTIONAL SEQUENCES and pepy
Message-ID: <9103271724.AA02050@rhino.ncsl.nist.gov>
Date: 27 Mar 91 17:24:13 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Distribution: inet
Organization: National Institute of Standards and Technology (NIST)
Lines: 56

This is a reposting of something I put out a week ago which was immediately
met with a deafening silence! Since it generated so much interest the first
time around, it occurred to me that you all might like to see it again, so
here it is	;^)

PS I figure the reason I got so few responses was either that I was way wide
of the mark and had missed some fundamental truth or that I had inadvertantly
discovered a genuine problem with pepy which has had all the ISODE people
scratching their heads ever since. My money is on the former, but I would
appreciate any feedback whatsoever - even RTFMs!


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I have a problem relating to how an application can discern between an
OPTIONAL SEQUENCE which is present but empty, and one which is absent,
based on the pepy decoder generated local C structure.

For example, if I have an ASN.1 definition:

DistributedOperationsArgument ::=
        SET {
            originator[0]
                DistinguishedName
                OPTIONAL,

            targetObject[1]
                DistinguishedName
                OPTIONAL,
        
                ...
}

...where DistinguishedName ::= SEQUENCE OF SomethingOrOther,
the corresponding pepy generated struct looks like this:

struct DistributedOperationsArgument {

    struct DistinguishedName *originator;

    struct DistinguishedName *targetObject;

                ...
};

Now, if originator == (struct DistinguishedName *)NULL, does that mean
(a) that originator was not present in the encoding, (b) that
originator was present but empty, or (c) either/both? In the case of
(a) or (b), what value of originator would indicate the converse?

Many thanks in advance for any insights.

        JT


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