[DFDL-WG] Possible DFDL spec errata

[Steve Hanson]

These were on the agenda for today's cancelled call.

2. Is parent/child alignment rule too strict?
 Spec property description for alignment says "The alignment of a child 
component must be less than 
 or equal the alignment of its parent element, sequence or choice". 
Experiments with creating DFDL schema
 from C structures have shown that this rule is violated. It seems 
unnecessary.  Specifically, C ensures that the alignment
 of objects in a repeating structure is preserved by rounding up the 
length of the structure, rather than aligning it.

 3. Does DFDL need to support signed integer types with lengthUnits 
'bits'?
 Spec only allows unsigned integers to have lengthUnits 'bits', but it is 
possible in C structures to delare
 bit fields for signed integers. They behave like two's complement. It 
looks like the spec is being 
 too restrictive in its types for 'bits'.

Regards

Steve Hanson
Architect, Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848
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Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU
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