I am afraid you have got this one the wrong way round. Without version
brackets, each line of the additions is treated as if it has been added
in a new version, and encodes exactly the same as if it had version
brackets round each line.
John L
Ed Day wrote:
>
> Hi,
>
> I am confused by this statement in the last response:
>
> "However, if you do not use version brackets, then each extension
> addition becomes a single addition group (implicitly in its own version
> brackets), and tail-end additions can then be omitted, because you can
> "pretend" you are an earlier version. "
>
> What is the definition of an 'extension addition'? I thought that without
> version brackets, you could only have a single addition and your only
> options were to include it in its entirety or omit the whole thing. Is this
> not true or am I missing something?
>
> Regards,
>
> Ed Day
> Principal Engineer
> Objective Systems, Inc.
> [EMAIL PROTECTED]
> (484) 875-3020 (main)
> (610) 608-4930 (mobile)
> (610) 321-0361 (fax)
> (877) 820-4164 (toll-free voicemail & fax)
>
> 5/2/2001 6:21:44 PM, John Larmouth <[EMAIL PROTECTED]> wrote:
>
> >Benoit POSTE wrote:
> >>
> >> John Larmouth wrote:
> >> > Benoit POSTE wrote:
> >> > > Or is the presence of each addition compulsory (baring DEFAULT
> >> > > or OPTIONAL components) if a later addition is present?
> >> > Yes. Presence of a later addition makes presence of an earlier one
> >> > mandatory. If the earlier one contains only optional elements, then the
> >> > flags that say whether they are present or not are mandatory, the actual
> >> > elements may be missing.
> >>
> >> Thanks Mr. Larmouth for answering that quickly.
> >> Just two more questions that arose from your answer ...
> >>
> >> If we consider a type with 3 additions (no OPTIONAL nor
> >> DEFAULT). Presence of the 3rd addtition makes presence of the 1st
> >> and 2nd ones mandatory. It is still legal to have a value with
> >> only the 1st and 2nd, but not the 3rd, right?
> >
> >There may be some confusion (that I have caused) here on what is an
> >addition.
> >
> >I was referring to additions added using version brackets - I *think*
> >you were, but I am not sure now.
> >
> >An addition group in version brackets has to be present (or the flags
> >saying elements are not present) in its entirety if a later one is
> >present.
> >
> >However, if you do not use version brackets, then each extension
> >addition becomes a single addition group (implicitly in its own version
> >brackets), and tail-end additions can then be omitted, because you can
> >"pretend" you are an earlier version.
> >
> >> And a PER question. If we have only OPTIONAL elements in an
> >> addition group, which are all missing. Then only the preamble
> >> mapping bit corresponding to that addition is mandatory, not the
> >> sequence-like presence flags for each element, right? (I seem to
> >> remember X.691 saying that the addition is considered non-present
> >> if all elements are absent)
> >
> >I need to check the spec on that, so will let someone else answer. I
> >also recollect similar text, but I am not sure. Wait for another reply.
> >
> >John L
> >
> >
--
========================================================================
Prof John Larmouth
1 Blueberry Road, Bowdon, Altrincham, Cheshire WA14 3LS, England.
j.larmouth @ salford.ac.uk Tel: +44 161 928 1605
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