[DFDL-WG] Suggest should be optional feature of DFDL - dfdl:utf16Width='variable' and other corner cases

[Mike Beckerle]

Given the limited set of required encodings for a conforming DFDL
processor, I believe dfdl:utf16Width='variable' should be an optional
feature.

That's just consistency with what is optional already. But it is also quite
hard to implement.

There are other situations that are very hard to implement, probably never
used by real users, yet which are non optional in the spec:

I would suggest that dfdl:lengthKind='explicit' for elements of complex
type, with dfdl:lengthUnits='characters' and a variable-width encoding like
utf-8 is very problematic to implement. I am pretty sure IBM DFDL has no
implementation of this per email threads, and I know I don't want to
implement this in Daffodil even though we're trying to be very
comprehensive in the implementation eventually.

I think implementations should be free to just not implement this.  These
sorts of cases often exist just because we're trying to preserve some
orthogonality of composition in the language. So it's possible to do quite
a few things that probably aren't ever needed by anyone, that reflect
ill-defined data formats, etc.

I'd rather not document a bunch of "non-conformances" for Daffodil or other
implementations for these sorts of things. I'd like to say we don't
implement them, but they're optional, and so that's allowed.

Comments?



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