You are correct on the first point - array steps must be indexed. I am happy to allow dfdl:occursCount() to work with non-array elements, so it could return 0 or 1 for an optional element. That's more elegant than casting the result of fn:exists() if you want an integer result. It is also consistent in that you can use dfdl:occursCount() wherever you have used dfdl:occursCountKind property. 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: Mike Beckerle <mbeckerle.dfdl@gmail.com> To: dfdl-wg@ogf.org, Date: 14/02/2013 21:42 Subject: [DFDL-WG] clarify array expressions Sent by: dfdl-wg-bounces@ogf.org Some folks are trying to create a DFDL model for IMF (internet message format ... basically email) There is this header structure which really wants unordered sequences. Since we don't have those yet I told them to use an array of choice like this: <xs:element name="hdrArray" minOccurs="1" maxOccurs="25"> <xs:complexType> <xs:choice> <xs:element ref="TO_HDR"/> <xs:element ref="FROM_HDR" /> </xs:choice> ... But then there are these contraints, like there should be only one FROM address, but there can be several TO addresses. So, one might want to write a DFDL expression using an XPath-like query path in it. E.g., <xs:assert>{ dfdl:occursCount( hdrArray/FROM_HDR ) eq 1 }</xs:assert> Here's the question: Is the DFDL expression in this assert legal? I advised them that no, it is not, because hdrArray is an array and isn't being indexed, while FROM_HDR is not an array, but is being used as the argument to dfdl:occursCount. I think DFDL's expression language is simply not powerful enough to express these constraints. I'm just looking for affirmation or discussion if there is more to say here. -- 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