Consider the following:

This is used to add a NUL at the end of a string, if the string length is less than the max length of 32. This comes up often in fixed length or variable-length-with-max data we've seen. I've put this terminator on a separate sequence after the element to emphasize that we're not scanning for terminating markup here. This has nothing to do with lengthKind 'delimited'.

However, the DFDL spec says (for terminator property)

· ES must not appear as the only DFDL string literal in the property. It can only appear as a member of a list.

· Neither the ES entity nor the WSP* entity may appear on their own as one of the string literals in the list when the parser is determining the length of a component by scanning for delimiters.

The second bullet doesn't apply to my example.

Re: first bullet, I think my terminator expression is illegal... because the '%ES;' is a list of literals containing ES as the only DFDL string literal.

But this is a really flawed constraint, as "%ES;%ES;" and "%ES; %ES;" both skirt the constraint, but mean the same thing as just "%ES;" which is illegal.

So, if we don't want to allow these hack workarounds, we need a statement that says runs of %ES; adjacent mean the same thing as one %ES;, and that more than one identical-meaning delimiter specified in a list of string literals means the same as just one. Or we can make these hack workarounds illegal.

However, why are we disallowing these?

The above construct in my example is very useful, and really hard to work around unless we can have a terminator that is '%ES;' as the only string literal. Actually I have no work around for this really. I am guessing I could come up with something, but the various things I've guessed at don't pan out, or prevent the string named 'value' above from being modeled as a simple type.

I know we don't want lengthKind='delimited' with terminator="%ES;" as that is most likely just a schema-definition error, but when we're not dealing with a lengthKind, we really do seem to need to specify situations where conditionally the terminator region will be empty.

So I think we need to do:

1) clarify that %ES; cannot be used in combination with any other character or entity as a member of a list of string literals.

1a) At the same time I would also disallow combinations of WSP* that are misleading and unnecessary i.e., disallow %WSP*; adjacent to any other WSP, WSP+, or WSP*.

2) clarify that the constraint that %ES; for terminator and separator cannot appear as the only string literal in a list of string literals... applies only when the parser is determining the length of a component by scanning for delimiters. This is just rephrasing the two bullets above so the clause about scanning applies to both, not just the second.

I believe this preserves the intent that when lengthKind="delimited" and we are scanning for delimiters, there must be *some* delimiter that is potentially not zero length. You still have to cope with the possible match being zero length due to %ES; being in the list of terminating markup, or WSP* similarly, with no whitespace found. But the notion that there is NO scanning to be done can't happen. That is, the notion that the schema specifies lengthKind delimited, but also specifies no delimiters at all, is still ruled out.

Comments?

Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | www.tresys.com

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