It boils down to what you want to appear in the infoset. If you want an element with a different name to appear for ease of identifying 'empty' then use #1. Otherwise use #2. I can't tell from just the snippet you sent, but depending on what level you have defined your initiator & terminator, <> for #2 will either result in nothing being added to the infoset, or PlainEmail being added. Regards Steve Hanson Architect, IBM Data Format Description Language (DFDL) Co-Chair, OGF DFDL Working Group IBM SWG, Hursley, UK smh@uk.ibm.com tel:+44-1962-815848 From: "Garriss Jr., James P." <jgarriss@mitre.org> To: "dfdl-wg@ogf.org" <dfdl-wg@ogf.org>, Date: 31/05/2013 14:15 Subject: [DFDL-WG] Better way to model "empty"? Sent by: dfdl-wg-bounces@ogf.org A return path email header can take two forms: 1. Plain email form: Return-path: <steve@tresys.com> 2. Empty form: Return-path: <> I’ve found 2 different ways to model this: #1 – with a choice <xsd:choice> <xsd:element name="Empty" type="xsd:string" dfdl:lengthKind="explicit" dfdl:length="0"/> <xsd:element name="PlainEmail" type="PlainEmail"/> </xsd:choice> #2 – with min/maxOccurs <xsd:element name="PlainEmail" type="PlainEmail" minOccurs="0" maxOccurs="1" dfdl:occursCountKind="implicit"/> When I’m faced with selecting one of these implementations over another, how do I think? What criteria should I be using? Is there another, better way that I haven’t even thought of? TIA-- 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