I did a quick search of the schemas on the github DFDL schemas site.
NITF has nillable elements. EDIFACT has nillable elements In EDIFACT case, empty strings become nilled elements. That's in-band for string. NITF has nillable dates, and nillable strings. Nillable strings are empty strings. Nillable dates are date elements containing all %SP; ie. all spaces. That's in band, because the dates are textual representation also. Many of the common mil data formats have a concept of "NO STATEMENT" which can be represented as either nilled elements, non-existing elements, empty elements, or an explicit <NOSTATEMENT/> element that is a marker. We're doing the latter. Arguably we should change this NO STATEMENT concept to one of the more conventional forms. I tend not to want to use empty elements because that creates ambiguity with empty string. Nilled elements are probably the natural choice here, as these elements are required, not optional. I don't have any examples off-hand of out-of-band nils used in a data format. But I will point out that XML's <foo xsi:nil="true"/> is itself an out-of-band nil representation. The attribute is a separate indicator out of band of the value space for the element. ________________________________ From: Costello, Roger L. <[email protected]> Sent: Wednesday, July 10, 2019 7:33:24 AM To: [email protected] Subject: Examples of file formats that use in-band nil? Examples of file formats that use out-of-band nil? Hello DFDL community, There are two ways file formats denote that a region has a nil value: * In-band nil: a symbol inserted into the region indicates nil. A part of the region’s value space is reserved for indicating nil. * Out-of-band nil: a symbol, separate from the region, indicates that the region has a nil value. I am seeking examples of each. Can you tell me a file format that uses in-band nil? Can you tell me a file format that uses out-of-band nil? /Roger
