Suggest should be optional feature of DFDL - dfdl:utf16Width='variable' and other corner cases
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 <http://www.ogf.org/About/abt_policies.php>
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@uk.ibm.com tel:+44-1962-815848 mob:+44-7717-378890 From: Mike Beckerle <mbeckerle.dfdl@gmail.com> To: "dfdl-wg@ogf.org" <dfdl-wg@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@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 -- dfdl-wg mailing list dfdl-wg@ogf.org https://www.ogf.org/mailman/listinfo/dfdl-wg Unless stated otherwise above: IBM United Kingdom Limited - Registered in England and Wales with number 741598. Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU
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