[DFDL-WG] lengthUnits 'bits' and binaryNumberRep

[Steve Hanson]

For discussion on next WG call:

The description of the dfdl:lengthUnits property for enum 'bits' says 
(after errata 2.90):

'bits' may only be used for xs:boolean, xs:byte, xs:short, xs:int, 
xs:long, xs:unsignedByte, xs:unsignedShort, xs:unsignedInt, and 
xs:unsignedLong simple types with representation 'binary'.

This is permitting binary numbers with dfdl:binaryNumberRep 'packed', 
'bcd' and 'ibm4690Packed' to have dfdl:lengthUnits 'bits'. That could make 
sense, as one could have an odd number of nibbles packed into the minimum 
space possible - eg a BCD range 000-999 could occupy 12 bits. 

However, the words that have been added for errata 2.90 (allowing signed 
number types to have lengthUnits 'bits') to both the description of 
dfdl:lengthUnits and section 12.3.7.2 have assumed that only 
binaryNumberRep 'binary' is allowed. 

I tested IBM DFDL with 12-bit 'packed' and 'bcd' reps packed back-to-back 
with bit alignment and it parsed them ok, but gave an error when 
serializing, saying that binaryNumberRep must be 'binary'.  Clearly 
incorrect because of the inconsistency, but what is the intent of the spec 
here?

Regards

Steve Hanson
Architect, IBM 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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