[DFDL-WG] Part 2 - Re: Action 307 - Demonstrate implementation interoperability - BOM

Wed Apr 3 05:44:41 EDT 2019

Ignore this, see other thread

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:   Steve Hanson/UK/IBM
To:     Mike Beckerle <mbeckerle.dfdl at gmail.com>
Cc:     DFDL-WG <dfdl-wg at ogf.org>
Date:   27/03/2019 16:15
Subject:        Re: Part 2 - Re: Action 307 - Demonstrate implementation 
interoperability - BOM

Hi Mike

The outstanding item to resolve is what to about BOMs.

307
Demonstrate implementation interoperability (Steve, Mike)
4/9: Need to make sure that DFDL spec section 21 lists a correct set of 
optional features, the implication being that Daffodil and IBM DFDL (and 
any other minimally conforming implementation) correctly implement the 
remaining required features. First step - see if there are any obvious 
omissions.
16/10: Steve sent email stating IBM DFDL's missing core features and 
non-compliant behaviour, and Mike responded. Discussion continuing via two 
separate email threads. Part 1 for core features. Part 2 for optional 
features. For the core features, agreed that the following needs to 
happen: 
1) IBM adds encodingErrorPolicy='replace'
2) Daffodil adds encodingErrorPolicy='error'
3) Daffodil ensures that, if not implementing default/fixed when parsing, 
it gives an SDE if a required occurrence has empty rep and element has 
default/fixed set.
4) A position is agreed on BOM handling - ongoing via email.
1/11: Just BOM to conclude on from the above list
15/11: Not discussed
29/11: No further progress.
10/1/19: 
1) IBM have started the work to add encodingErrorPolicy='replace'. 
2) Daffodil have a temp setting to tolerate encodingErrorPolicy='error' 
with a warning. 
3) Daffodil to investigate whether this is feasible.
4) More discussion needed on BOM
7/2: Updates:
1) In progress
2) As above.
3) In progress
4) No progress

I can't find the email thread the action mentions, but my thoughts are as 
follows:

There are 3 options - 
        a) keep the spec as it is which implies BOM processing is core - a 
problem as neither Daffodil nor IBM DFDL implement it
        b) make BOM processing optional - which means there would need to 
be a property to switch it on or off in case an implementation started to 
support it later
        c) remove BOM processing altogether from 1.0 and add to the 2.0 
list

I am leaning towards c) on the following grounds:
- Only one customer that I know of ever requested BOM processing for 
non-XML data (in 2010, for MRM, before IBM DFDL available)
- BOM processing only applies to the message as a whole, not to any 
embedded Unicode fragments, so support is selective anyway
- It is possible to model an optional BOM and use it to set a user-defined 
encoding variable which is then used by the rest of the schema

I have a schema that models BOM and it successfully parses and unparses 
the 3 variants fine (no BOM present, BOM for BE present, BOM for LE 
present).

If you have the BOM email thread please can you forward it, so I can see 
if I have missed any part of the thought process? 

I have found the original DFDL WG thread from 2011 when we added BOM 
support to the spec via erratum 3.7, which discusses the original 
motivation and design, I'll send you it.

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:   Steve Hanson/UK/IBM
To:     Mike Beckerle <mbeckerle.dfdl at gmail.com>
Cc:     DFDL-WG <dfdl-wg at ogf.org>
Date:   09/10/2018 12:16
Subject:        Re: Part 2 - Re: Action 307 - Demonstrate implementation 
interoperability

Mike, responses in-line below.

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:     Steve Hanson <smh at uk.ibm.com>
Cc:     DFDL-WG <dfdl-wg at ogf.org>
Date:   04/10/2018 00:50
Subject:        Part 2 - Re: Action 307 - Demonstrate implementation 
interoperability

Based on Daffodil JIRA ticket backlog, and documentation at 
https://daffodil.apache.org/unsupported/, below are DFDL non-core features 
that are not supported by Daffodil, but that seem to be supported by IBM 
DFDL (based on my not finding anything that says they aren't implemented), 
and so are possibly in use in DFDL schemas we will need to use for 
interoperability testing.

Please advise if IBM DFDL does *not* implement any of these. 

* default, fixed - for defaulting values at parse time - Daffodil support 
for this is partial at parse time, unsupported at unparse time. The fixed 
attribute isn't supported at all.
* unordered sequences. IBM DFDL does not support default/fixed when 
parsing (see other thread).
* byte-value entities - in contexts other than fillByte
* ICU symbols 'u' and 'I' in calendarPattern
* binaryFloatRep 'ibm390Hex'
* documentFinalTerminatorCanBeMissing
* textStandardBase - with value not equal to 10
* lengthKind 'prefixed', and prefixIncludesPrefixLength, prefixLengthType 
- Note IBM restricts prefixLengthType to a type that itself cannot be 
prefixed. Correct.
* assert with failure type 'recoverableError'
* calendarObserveDST
* calendarCenturyStart
* textNumberPattern 'V' and 'P' symbols
* CCSID for specifying dfdl:encoding
* nilKind 'literalValue' for binary data
* choiceLengthKind 'explicit' and choiceLength
* separatorSuppressionPolicy - behaviors for these in Daffodil are known 
to be both non-standard currently and also different from IBM DFDL. This 
needs correcting. IBM DFDL does not support 'trailingEmptyStrict'
.

The above list (after review/correction) needs to be crossed with the 
published DFDL schemas on github that were published by IBM. The features 
required to run those DFDL schemas are required for Daffodil to implement 
before the interoperability demonstration. 

Below are features of DFDL I believe neither IBM DFDL nor Daffodil 
implement, and as they are non-core, they need not be implemented by 
either for interoperability testing:

* lengthKind 'endOfParent'
* nilKind 'logicalValue'  IBM DFDL implements this.
* occursCountKind 'stopValue' (and occursStopValue)
* textBiDi - and other related biDi properties
* useNilForDefault IBM DFDL implements this
* floating
* fn:exactlyOne function
* fn:namespace-URI() function
* dfdl:escapeCharacterPolicy 'delimiters' - daffodil doesn't implement 
this property at all.

Below are features of Daffodil that are not implemented by IBM DFDL and so 
cannot be used in schemas created using Daffodil that intend to be 
interoperable. These are either easy to work around, or impossible to work 
around, so are not a big deal, they just have to be kept in mind if 
considering a DFDL schema for use in interoperability testing. This 
includes schemas published on github, for image formats, CSV, etc.,  and a 
number of the FOUO schema published on DI2E.net/forge.mil - some of those 
quite possibly can work with IBM DFDL, and if they can do so, they should 
be modified so that they can be included in the interoperability testing. 

The list below mostly comes from 
https://www.ibm.com/support/knowledgecenter/en/SSMKHH_10.0.0/com.ibm.etools.mft.doc/df00150_.htm

* calendarTimeZone specified as "" (empty string)  - This is the most 
problematic one, so I've put it first. The predefined DFDL named format 
that is supplied with Daffodil and used as a starting point by most 
schemas has calendarTimeZone="". This is because customers didn't like 
that their datetimes were all being appended with "+00:00" for UTC time 
zone (in the infoset) when the data simply didn't specify a time zone. 
Schemas intended for interoperability testing should specify 'UTC' for 
this property.
* calendarTimeZone specified as an Olson format time zone
* inputValueCalc, outputValueCalc
* hiddenGroupRef
* Asserts and discriminators on simple type definitions or global element 
definitions
* fn:concat with more than 4 arguments
* non-8-bit charset encodings
* bitOrder not mostSignifcantBitFirst
* '@' in textNumberPattern (TBD: unsure if Daffodil has this)
* "_" in calendarLanguage
* calendarLanguage an expression
* assert & discriminator messages an expression 
* binaryBooleanTrueRep as "" (empty string) 
* checks for binary packed numbers with length units 'bits' and not a 
multiple of 4 length, and similarly for alignmentUnits bits and alignment 
not multiple of 4. (relevant to negative tests only)
* lengthKind 'implicit' complex elements inside lengthKind 'delimited' 
complex elements.

Additionally IBM DFDL contains these bugs in its expression processing:
1) Path locations are not correctly validated. Specifically, array 
elements without predicates and references into other choice branches are 
not flagged as errors.
2) In DFDL expression functions, the namespace prefixes for  
http://www.w3.org/2001/XMLSchema and 
http://www.w3.org/2005/xpath-functions" must be 'xs' and 'fn' 
respectively, even if not declared.
3) In DFDL expressions, namespace prefixes in paths are ignored and 
matching is against element name only. 

For interoperability testing therefore:
- For 1) avoid the use of either example 
- For 2) always declare xmlns:xs and xmlns:fn and always use those 
prefixes in expressions
- For 3) avoid sibling elements that have same name but different 
namespace; use elementFormDefault="unqualified" to avoid namespaces for 
local elements altogether 

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

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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