In an earlier email exchange on this subject, I suggested the use of an
escape scheme to handle this, assuming that the { } are either both absent
or both present, using properties escapeKind 'escapeBlock',
escapeBlockStart '{', escapeBlockEnd '}'. The disadvantage of this
approach is when serializing - you need to set property
generateEscapeBlock to 'always' or 'whenNeeded' - there is no setting for
'remember what it was when parsed'. That may or may not be a requirement
here.
If an escape scheme is not appropriate, then whether the 'choice' or
'sequence with optionality' approach is best is really up to you. It all
depends on how you want to manipulate the infoset subsequently. The
'sequence' is more flexible as it gives you the possibility of hiding the
brackets from the infoset using dfdl:hiddenGroupRef.
To Jonathan's point, if the { } are either both absent or both present.
you can place a dfdl:assert on the sequence which throws an error if the
brackets are unbalanced.
Regards
Steve Hanson
Architect, Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh@uk.ibm.com
tel:+44-1962-815848
From: "Cranford, Jonathan W."
To: "Garriss Jr., James P." , "dfdl-wg@ogf.org"
,
Date: 08/03/2013 21:29
Subject: Re: [DFDL-WG] Optional Initiator and Terminator?
Sent by: dfdl-wg-bounces@ogf.org
I don’t know the answer to the DFDL portion of your question, but I can
say your two workarounds aren’t equivalent. The latter will accept an
initiator with no terminator, and vice versa (e.g., “{ data” and “data }”,
while the former will not.
HTH,
Jonathan
From: dfdl-wg-bounces@ogf.org [mailto:dfdl-wg-bounces@ogf.org] On Behalf
Of Garriss Jr., James P.
Sent: Friday, March 08, 2013 12:42 PM
To: dfdl-wg@ogf.org
Subject: [DFDL-WG] Optional Initiator and Terminator?
Is there a way to specify that an initiator/terminator pair is optional?
IOW, these are both valid:
{ data }
data
If not, which of these workarounds is better (and why)?
Choice
DataWithInitiatorAndTeminator
DataWithoutInitiatorAndTeminator
Or
Sequence
OptionalInitiator (0 to 1)
Data
OptionalTerminator (0 to 1)
These seem the same to me, but maybe there’s a reason why one is better.--
dfdl-wg mailing list
dfdl-wg@ogf.org
https://www.ogf.org/mailman/listinfo/dfdl-wg
Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number
741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU