The first form is looking at the physical data and seeing if its length is 0 bytes. It can be used for any simple type. The second form is looking at the logical value of the data and seeing it has the value empty string. It can be used only is type is xs:string or xs:hexBinary. Only if the type of Empty is xs:string or xs:hexBinary are these functionally equal. 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: 03/06/2013 13:40 Subject: [DFDL-WG] 0 equals ""? Sent by: dfdl-wg-bounces@ogf.org When are these not functionally equal? <dfdl:discriminator>{ dfdl:valueLength(../Empty, "bytes") eq 0 }</dfdl:discriminator> <dfdl:discriminator>{ ../Empty eq "" } </dfdl:discriminator> 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