Finally had some time to look at the TLOG stuff again (the format emitted by IBM 4680 & 4690 POS controllers). This time I've looked at the MRM code, & spoken with domain expert David Bennett, to establish the full behaviour. Unfortunately there are some issues which mean DFDL 1.0 is not capable of handling it.

1. The individual fields are a mixture of ASCII strings, proprietary packed strings (rare), proprietary packed decimals, binary integers (rare). All fields are delimited by a separator.

2. The fields are all defined with a length in bytes, but most of the string and decimal fields are actually variable length. If the data exceeds the length in bytes when parsing or unparsing the MRM throws an error. However, talking to David B, the length is really intended to be used if there was ever a fixed length equivalent format, so is really for validation only. To parse the current TLOG formats it is sufficient to use the delimiter.
Note to WG: Validation using the specified length only works for strings. Should we allow dfdl:length to be specified when dfdl:lengthKind=delimited or pattern, and use it as an extra constraint when parsing/unparsing?

3. Scanning for the separator, or maybe use of a data pattern, is needed to extract the variable length data, including packed decimal data (which we would consider a binary type).
Note to WG: Should we allow binary scanning when the users says it is safe to do so?

4. Packed strings. This is a packed data type used when the range of possible chars in the string is limited to 0-9, A-F. You can view this as a BCD that can also carry A-F. MRM does not try to turn this into an integer, instead it treats it as character data. That is x12x34 would result in string '1234'. Odd numbers of digits are padded with a x0 nibble. On unparsing the MRM throws an error if a character other than 0-9, A-F is encountered.  In practice, these packed strings are rare and invariably only carry 0-9 anyway. I'm still trying to establish why this data type is needed, as it could be treated as a logical integer and modelled as BCD.

5. Packed decimals. Like a packed decimal in the IBM sense. These can carry negative numbers but use a leading xD sign nibble. No sign nibble if positive. Odd number of digits (including sign if present) are padded with xF nibble. This is best illustrated using examples.
1234     =>     x12x34
123      =>     xF1x23
-1234    =>     xFDx12x34
-123     =>     xD1x23
Note to WG: Should we support this data type natively?

6. Some of the packed decimals are interpreted as an array of bit flags. I assume that DFDL would model these using dfdl:hidden.

Regards

Steve Hanson
Programming Model Architect, WebSphere Message  Brokers,
OGF DFDL WG Co-Chair,
Hursley, UK,
Internet: smh@uk.ibm.com,
Phone (+44)/(0) 1962-815848


From: Alan Powell/UK/IBM@IBMGB
To: dfdl-wg@ogf.org
Date: 19/01/2010 18:40
Subject: [DFDL-WG] Agenda for OGF DFDL WG call 20 January        2010-        13:00        UK        (8:00 ET)
Sent by: dfdl-wg-bounces@ogf.org





1.   045  - Disciminators
Mike was writing up proposal

2  Unparsing lengthKind = 'pattern'
Review email from Alan

3. TLOG
SteveH has been investigating

4, Empty Sequences
Is the current section correct

1.1        Empty Sequences

A sequence having no children is syntactically legal in DFDL; however, a sequence having no children must have content length zero. It can still have non-zero length Prefix and Suffix regions, but the SequenceContent region in between must be of length zero. It is a schema definition error if the SequenceContent region of an empty sequence is not length zero.


5. Mike review issues
Attached document gives replies to comments/issues. Ones without replies need to be discussed


6. Go through remaining actions

7 Review Schedule
Activity
Schedule
Who
Complete Action items
             - 18 Dec 2009
 WG
Complete Spec Write up work items
            – 23 Dec 2009
AP
Restructure and complete specification
              - 23 Dec 2009
AP
Issue Draft 038
23 Dec 2009
WG review WG review
7 Dec – 08 Jan 2010
WG
Incorporate review comments
4 Jan - 29 Jan 2010
AP +
Issue Draft 039
15 Jan 2010
Incorporate review comments
4 Jan - 29 Jan 2010
AP +
Issue Draft 040
29 Jan 2010
Initial OGF Editor Review Initial Editor review
1 Feb - 1 Mar 2010
OGF
Initial GFSG review
1 Feb - 1 Mar 2010
Issue Draft 041
1 Mar 2010
OGF Public Comment period (60 days)
1 Mar - 30 Apr 2010
OGF
OGF 28 Munich
15-19 March 2010
Incorporate comments Incorporate comments
28 May 2010
Issue Draft 042
28 May 2010
Final OGF Editor Review Final  Editor review
June  2010
OGF
final GFSG review
June  2010
Issue Final specification
30 June 2010
Publish proposed recommendation
1 July 2010
Grid recommendation process
1 Jan - 1 April 2011



Current Actions:
No
Action
045
20/05 AP: Speculative Parsing
27/05: Psuedo code has been circulated. Review for next call
03/06: Comments received and will be incorporated
09/06: Progress but not discussed
17/06: Discussed briefly
24/06: No Progress
01/07: No Progress
15/07: No progress. MB not happy with the way the algorithm is documented, need to find a better way.
29/07: No Progress
05/08: No Progress. Will document behaviour as a set of rules.
12/08: No Progress
...
16/09: no progress
30/09: AP distributed proposal and others commented. Brief discussion AP to incorporate update and reissue
07/10: Updated proposal was discussed.Comments will be incorporated into the next version.
14/10: Alan to update proposal to include array scenario where minOccurs > 0
21/10: Updated proposal reviewed
28/10: Updated proposal reviewed see minutes
04/11: Discussed semantics of disciminators on arrays. MB to produce examples
11/11: Absorbing action 033 into 045.  Maybe decorated discrminator kinds are needed after all. MB and SF to continue with examples.  
18/11: Went through WTX implementation of example. SF to gather more documentation about WTX discriminator rules.
25/11: Further discussion. Will get more WTX documentation. Need to confirm that no changes need to Resolving Uncertainty doc.
04/11: Further discussion about arrays.
09/12: Reviewed proposed discriminator semantic.
16/12: Reviewed discriminator examples and WTX semantic.
23/12: SF to provide better description of WTX behaviour and invite B Connolley to next call
06/01:B Connolly not available. SF to provide more complete description.
13/01: Stephaine took us through a description of WTX identifiers. Mike agreed to write up in DFDL terms.
049
20/05 AP Built-in specification description and schemas
03/06: not discussed
24/06: No Progress
24/06: No Progress (hope to get these from test cases)
15/07: No progress. Once available, the examples in the spec should use the dfdl:defineFormat annotations they provide.
...
14/10: no progress
21/10: Discussed the real need for this being in the specification. It seemed that the main value is it define a schema location for downloading 'known' defaults from the web.
28/10: no progress
04/11: no progress
11/11: no update
18/11: no update
25/11: Agreed to try to produce for CSV and fixed formats
04/12: no update
09/12: no update
16/12: no update
23/12: no update
06/01: no progress. If there is no resource to complete this action it can be deferred
13/01:no progess
064
MB/SH Request WG presentation at OGF 28
25/11: Session requested
04/12: no update
09/12: no update
16/12: SH has changed request to a general session rather tha WG in the hope of attracting more people.
23/12: no update
06/01: not heard anything yet
13/01: no update
066
Investigate format for defining test cases
25/11:IBM to see if it is possible to publish its test case format.
04/12: no update
09/12: no update
16/12: reminded dent to project manager
23/12: SH will send another reminder.
06/01: Another reminder will be sent
13/01: no update
068
Should the roots of messages be designated.?
09/12: Yes. New dfdl:documentRoot property
Closed
16/12: reopened and decided to drop property subject to agreement from SKK and SF
23/12: SKK review decision to drop  dfdl:documentRoot
13/01: closed
071
Semantics of length=0, nil handling and defaults.
23/12:SH no update
06/01: SH has started
13/01: SH proposal review. Minor updates to be made
073
SH: Control of overpunching zoned positive sign
13/01: no update



Alan Powell

MP 211, IBM UK Labs, Hursley,  Winchester, SO21 2JN, England
Notes Id: Alan Powell/UK/IBM     email: alan_powell@uk.ibm.com  
Tel: +44 (0)1962 815073                  Fax: +44 (0)1962 816898


Unless stated otherwise above:
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