Yeah, this part of the DFDL spec has some clarity issues.
The "data" never means the infoset (the XML output if you are using XML). It always refers to the data or data stream being parsed from, or unparsed to. We try to use data stream to be clearer here. That's what the intention is. There could be slips in the spec where data is used but "infoset" was intended. I don't know of those, but there's the possibility. Trailing position means, in a sequence, that the item could be the last element or model-group in the sequence. That requires that everything after it is in some way optional, so that there might not be data representation for it, and hence, there may not be a need for a separator in the data stream for separating its representation. So imagine a comma separated sequence of 5 elements, each an integer. They're all optional (minOccurs="0"). All these elements are potentially trailing, the question is just whether they are actually present and the last thing, or there's something after them. Here's some example lines 1,2,3,4,5 1,,,,5 1,2 // ok with trailingEmpty or trailingEmptyStrict 1,,,, // Illegal if trailingEmptyStrict, but allowed by trailingEmpty ________________________________ From: Costello, Roger L. <[email protected]> Sent: Friday, December 21, 2018 2:51:16 PM To: [email protected] Subject: What is a trailing occurrence? Hello DFDL community, The DFDL specification has this: separatorSuppressionPolicy Implications trailingEmptyStrict Positional sequence where trailing occurrences that have zero length representation MUST be omitted from the data, along with their associated separator. What is “trailing occurrence”? Does it imply the separator is in prefix position and hence the string (occurrence) is trailing (after the separator)? Also, the above quoted text says: omitted from the data. What data? Does the word “data” refer to the XML output? /Roger
