[DFDL-WG] bit order documents updated

Fri Jul 25 09:45:17 EDT 2014

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
<http://www.ogf.org/About/abt_policies.php>

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*
> <http://www.ibm.com/developerworks/library/se-dfdl/index.html>
> Co-Chair, *OGF DFDL Working Group* <http://www.ogf.org/dfdl/>
> IBM SWG, Hursley, UK
> *smh at uk.ibm.com* <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* <http://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>
>
>
>
> On Thu, Jul 24, 2014 at 5:16 PM, Mike Beckerle <*mbeckerle.dfdl at gmail.com*
> <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*
> <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* <http://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>
>
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