[DFDL-WG] Suggest should be optional feature of DFDL - dfdl:utf16Width='variable' and other corner cases
Steve Hanson
smh at uk.ibm.com
Tue Sep 13 08:15:21 EDT 2016
Mike
I am assuming that the processing for utf-16 'fixed' or 'variable' is
entirely handled by ICU so there should be no coding overhead.
IBM DFDL works ok for dfdl:lengthKind='explicit' for an element of complex
type with dfdl:lengthUnits='characters' and dfdl:encoding="utf-8". But
there are conditions the content of the complex type must satisfy
otherwise an SDE results, such as:
CTDV1524E : For a complex element, when 'lengthKind' is 'explicit' or
'prefixed', and 'lengthUnits' is characters, all simple child elements
must have text representation, 'lengthUnits' set to 'characters' and the
same encoding.
So we insist that the properties of the children are consistent with the
properties of the parent. If you recall, IBM DFDL does all these kinds of
validation checks in a pre-processing phase.
That seems a pretty sensible rule but I am not sure if the rule appears in
the spec as such - I just had a quick look but didn't spot anything.
So I guess I don't see a need for these things to be optional features?
Regards
Steve Hanson
IBM Integration Bus, Hursley, UK
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
smh at uk.ibm.com
tel:+44-1962-815848
mob:+44-7717-378890
From: Mike Beckerle <mbeckerle.dfdl at gmail.com>
To: "dfdl-wg at ogf.org" <dfdl-wg at ogf.org>
Date: 10/08/2016 18:57
Subject: [DFDL-WG] Suggest should be optional feature of DFDL -
dfdl:utf16Width='variable' and other corner cases
Sent by: "dfdl-wg" <dfdl-wg-bounces at ogf.org>
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
Please note: Contributions to the DFDL Workgroup's email discussions are
subject to the OGF Intellectual Property Policy
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