[DFDL-WG] Behavior of nilKind literalValue with respect to binaryNumberRep of packed

Wed Apr 15 10:51:33 EDT 2020

There is no explicit control over justification and trimming for binary 
data. For a specific type of binary data, it is what it is. Packed 
decimals for example are always right-justified.

I don't think interpreting x00x00x0F as a nil value is a good idea. 
Typically this is unsigned zero, but it is a valid number and not an 
out-of-type value. I can see that one might want to use xFFFFFFF or 
x000000 as nil, as these values are often blatted into storage by (eg 
COBOL) programs and both are out-of-type (although you can handle the 
latter as zero using dfdl:binaryPackedSignCodes property).  The way you 
handle these as nil is using dfdl:nilLiteralCharacter, set to "%#rFF" or 
"%#r00" respectively, which handles the variable length. There is no way 
to provide a nil literal value for a variable length binary element, 
because no trimming takes place.

Regards

Steve Hanson
IBM Hybrid Integration, Hursley, UK
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
smh at uk.ibm.com
tel:+44-1962-815848
mob:+44-7717-378890
Note: I work Tuesday to Friday 

From:   Mike Beckerle <mbeckerle.dfdl at gmail.com>
To:     Bradd Kadlecik <braddk at us.ibm.com>
Cc:     DFDL-WG <dfdl-wg at ogf.org>
Date:   14/04/2020 23:57
Subject:        [EXTERNAL] Re: [DFDL-WG] Behavior of nilKind literalValue 
with respect to binaryNumberRep of packed
Sent by:        "dfdl-wg" <dfdl-wg-bounces at ogf.org>

Can you give what the bytes look like for typical values of various sizes 
small and large,  how their length is determined, and what a nil value 
looks like in bytes?

Mike Beckerle | OGF DFDL Workgroup Co-Chair | Owl Cyber Defense | 
www.owlcyberdefense.com
Please note: Contributions to the DFDL Workgroup's email discussions are 
subject to the OGF Intellectual Property Policy

On Tue, Apr 14, 2020 at 4:54 PM Bradd Kadlecik <braddk at us.ibm.com> wrote:
Yes that works for fixed length but not variable length which is possible 
for packed decimal with bigEndian.

Regards,

Bradd Kadlecik
z/TPF Development

Phone: 1-845-433-1573
E-mail: braddk at us.ibm.com
2455 South Rd
Poughkeepsie, NY 12601-5400
United States

Mike Beckerle ---04/14/2020 03:56:45 PM---Not sure I understand the 
mixture of the concepts of justification and packed decimal here.

From: Mike Beckerle <mbeckerle.dfdl at gmail.com>
To: Bradd Kadlecik <braddk at us.ibm.com>, DFDL-WG <dfdl-wg at ogf.org>
Date: 04/14/2020 03:56 PM
Subject: [EXTERNAL] Re: [DFDL-WG] Behavior of nilKind literalValue with 
respect to binaryNumberRep of packed

Not sure I understand the mixture of the concepts of justification and 
packed decimal here. 

I usually think of packed decimal as fixed length and without padding. 

Let me assume this example: 12345C is value 12345, 00000C is zero, and 
00000F is the nil indicator. 

So, bigEndian byte order, I think dfdl:nilvalue="%#r00;%#r00;%#r0F;" is 
what I'd expect to see for a literalValue nilValue to match that. 

I'm guessing some assumption in the above doesn't match your use case, so 
please correct.

Mike Beckerle | OGF DFDL Workgroup Co-Chair | Owl Cyber Defense | 
www.owlcyberdefense.com
Please note: Contributions to the DFDL Workgroup's email discussions are 
subject to the OGF Intellectual Property Policy

On Tue, Apr 14, 2020 at 2:59 PM Bradd Kadlecik <braddk at us.ibm.com> wrote: 
I think there is a problem when the literalValue is left-justified for 
binary data such as packed decimals. This seems problematic because a "0" 
value might be indicated by having the last byte be 0x0C for a signed 
numeric while a nil value might be desired to be understood by having the 
last byte be a 0x0F. In both cases, all preceding bytes are 0x00. In the 
case that the packed decimal is of variable length, there seems no way to 
represent this nil value unless it is understood that the fillByte is used 
for the area preceding the NilElementLiteralContent. Apologies if I might 
of missed some clarification made regarding this.

Regards,

Bradd Kadlecik
z/TPF Development

Phone: 1-845-433-1573
E-mail: braddk at us.ibm.com
2455 South Rd
Poughkeepsie, NY 12601-5400
United States

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