[DFDL-WG] bit order documents updated

Fri Aug 1 08:00:18 EDT 2014

Mike

Attached is a review copy of the bit order document with Word comments 
added.  I am particularly concerned about the grammar region implications 
that you have added. We have not discussed this before on the calls.

Regards

Steve Hanson
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848

From:   Mike Beckerle <mbeckerle.dfdl at gmail.com>
To:     Steve Hanson/UK/IBM at IBMGB, "dfdl-wg at ogf.org" <dfdl-wg at ogf.org>, 
Date:   25/07/2014 14:45
Subject:        Re: [DFDL-WG] bit order documents updated

I will edit and share a discussion thread of the link16 requirements I 
have been having with Russ Hawkins of Lockheed-Martin discussing 
TDL/link16. He is a SME on this topic, having built and used processors 
for that format.

MIL-STD-2045 works today with just the leastSignificantBitFirst feature as 
described. We have some tests. I will publish this DFDL schema and tests. 

MIL-STD-2045 doesn't require the byte order mixed-endian behavior. 

Mixed endian behavior is something we originally thought link16 required 
that is not illustrated within MIL-STD-2045. 

Our understanding of link16 was incorrect however. It turns out link16 
only requires this byte/word swapping as a bulk preprocessing pass over 
the entire body of a message (but not the message header). This is not 
unlike decoding base64 or other encoded data found in a message payload. 
DFDL can't do this today in one pass - an application program that drives 
a DFDL processor is needed for multi-pass formats like this. This is fine 
for DFDL v1.0.  

Russ verified that this is the *only* byte/word swapping required for 
link16 - there is no per-element mixed-endian byte order required. Just 
the same least-significant-bit-first bitOrder that MIL-STD-2045 needs. 
Hence, I dropped the mixed-endian byte order from the proposal.

The remaining link16 requirement that couldn't be worked around is the 
6-bit ascii format. 

It is always going to be the case that for some formats, especially these 
big complex ones, that we will not really know if we can model it until 
the DFDL schema has been created. However, MIL-STD-2045 plus a minor 
additional 6-bit encoding is our best shot at having credible support for 
a wide array of MIL-STD formats. 

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

On Fri, Jul 25, 2014 at 6:02 AM, Steve Hanson <smh at uk.ibm.com> wrote:
I am very concerned that we do not understand these formats properly. We 
need to engage an SME to verify that these proposals are enough to model 
MIL-STD-2045 and Link-16 (and other related formats). Until that happens 
IBM will not be able to close action 233. 

Regards

Steve Hanson
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848 

From:        Mike Beckerle <mbeckerle.dfdl at gmail.com> 
To:        "dfdl-wg at ogf.org" <dfdl-wg at ogf.org>, 
Date:        24/07/2014 23:08 
Subject:        Re: [DFDL-WG] bit order documents updated 
Sent by:        dfdl-wg-bounces at ogf.org 

Of course as soon as I post this I get the information needed to resolve 
several things. 

The new byte-order enum is not needed, so I removed that material. The bit 
order document is now a fairly clean thing trying to be an errata.

Please review: draft-gwdi-bit-order-features-v3.0.docx

I created a separate working document on "Mixed Endian Byte Order" should 
we ever take this up again.

I also removed the TDML stuff into the TDML document. (now v2). 

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 

On Thu, Jul 24, 2014 at 5:16 PM, Mike Beckerle <mbeckerle.dfdl at gmail.com> 
wrote: 

There are now several working documents having to do with bit-order. The 
prior document has been taken down and replaced by 3 others.

These are all up on redmine: 
http://redmine.ogf.org/dmsf/dfdl-wg?folder_id=5485 

1) draft-gwdi-bit-order-features-v2.05.docx - Just describes the new 
features + TDML extension. The biggest section is organized like an errata 
specifying where things change in the spec. This should get incorporated 
into errata, or perhaps just referenced from an errata. 

Section 3 of this doc is the proposed errata and spec language for review. 

There is one major open issue here, which is it is unclear whether the 
mixed-endian byte order that was previously proposed is actually needed or 
not. The swapping of 16-bit words appears to be not a per-element thing, 
but something done as a pre-processing of an entire message body before 
parsing. This isn't something we can handle in DFDL, much like 
base64-encoded data and so forth. This may be the only place that needed 
the 16-bit word swapping. 

2) Understanding Bit Orderings - 
draft-gwdi-mil-std-2045-understanding-bit-order-v2.05.docx - Material 
about bit order - the Wire model vs. Number model material. This is 
effectively just archiving this material for posterity.

If you already read this, you don't need to read it again. 

3) draft-gwdi-mil-std-2045-additional-features-v2.05.docx - Material about 
additional DFDL features that would be helpful in modeling MIL-STD-2045.

This can also be reviewed. Not as urgent as (1) above. 

4) draft-gwdi-dfdl-standard-encodings-v03.docx - This is material that 
will be integrated back into the spec as an appendix, but this 
incorporates feedback on prior versions, and adds a 6-bit ascii encoding 
that is used by the same binary format standards as the 7-bit one. Works 
same way, just 6 bits not 7, so there's some codepoint changes.

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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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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