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." <jcranford@mitre.org> To: "Garriss Jr., James P." <jgarriss@mitre.org>, "dfdl-wg@ogf.org" <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