Open Grid Forum: Data Format Description Language Working Group
OGF DFDL Working Group Call, July 14-2010
Attendees
Steve Hanson (IBM)
Alan Powell (IBM)
Stephanie Fetzer (IBM)
Tim Kimber(IBM)
Suman Kalia (IBM)
Apologies
Mike Beckerle (Oco)
1. Current Actions
Updated below
2 Nils and Defaults.
Discussed Alan updates (v9). Updates still needed.
3. using textStringPadCharacter with charRef '%#r' on multi-byte encoding
textStringPadCharacter
DFDL String literal
The padding character or byte value that is used when justifying or
trimming text elements.
A pad character can be specified using a literal or DFDL entities.
A pad byte value must be specified using the %#r entity.
DFDL validation rules
- if a pad character is specified when lengthUnits='bytes' then the pad
character must be a single-byte character.
- if a pad byte value is specified when lengthUnits='characters' then the
encoding must be a fixed-width encoding. Padding and trimming is be
applied using an array of N pad bytes values, where N is the width of a
character in the fixed-width encoding.
Annotation: dfdl:element, dfdl:simpleType
Would adding fillByte to dfdl:textPadKind enumeration make it clearer.
padChar is a pad character (%#r not allowed)
fillByte is a fill byte
Although there was some merit in having separate textPadKinds it was felt
it was too late to make the change. The property descriptions (for
numbers, calendars and booleans as well) will be improved as above.
4. nilIndicatorPath and nilIndicatorIndex properties
These properties seem a bit of an anomaly. Tim has suggested they can be
simplified.
Tim had emaled Mike with a proposal and Steve had responded with 3
alternatives
1) Leave things as they are, perhaps renaming 'nilIndicator' to
'indicator'
2) Collapse nilIndicatorPath and nilIndicatorIndex to a single property.
It means the path is repeated, but it makes nils consistent with length
and occurs. For all, you can always use a string variable to hold the
constant part of the path and concatenate with the index. And if we
improve usability in a future DFDL release, we would improve it for nils,
lengths and occurs at the same time.
3) Drop the properties for 1.0 altogether on the grounds that it is a rare
case. I've never seen such a format, but we know Mike has.
As part of nils default discussion the WG decided to drop
dfdl:nilIndicator and dfdl:nilIndicatorIndex as it was felt the
complications it introduced on unparsing were not worth the additional
function. This may be revisited for DFDL v2.
5. Alignment enumerations when dfdl:lengthUnits = 'bits'
When alignmentUnits='bits', the rule that alignment must be 1,2,4,8 etc or
multiple of 2 looks rather hard to justify.
We should either
a) remove the rule entirely and allow any postiive integer > 1 or
b) make the rule apply only when alignmentUnits='bytes'
It was agreed to remove the restriction on aligmentUnits for both 'bytes'
and 'bits'.
Also suggested that a note should be added to the default alignment and
implicit length tables that 'although the values are specified in bits
that does not imply that the dfdl:lengthUnits can be specified as 'bits'
for all the simple types
6. Semantics of 'fixed'
Not discussed. Action Raised.
7. Clarify the specification of error reporting from a DFDL processor
- section 2.3 needs to be updated
Not discussed. Action Raised
8 Asserts and discriminators
- specify the scope of forward references. Must be downward-only. The
expression must be resolvable by the time the component on which it is
positioned goes out of scope - otherwise it is a processing error.
Not discussed. Action Raised
9 Expressions
Discuss error behaviour when evaluating an expression in various contexts
- All properties:
wrong type returned : schema definition error
exception when evaluating expression : schema definition error
referenced variables/paths not available : schema definition error
- Properties which allow a forward reference
referenced variables/paths not available : no error. DFDL processor
continues processing until the expression result is available, then acts
on the result.
Not discussed. Action Raised
10. Grammar for DFDL expression
- currently allows multiple predicates on a single expression. Sounds as
if this was unintended.
Not discussed. Action Raised
Meeting closed, 17:00
Next call Wednesday 21 July 2010 15:00 UK (10:00 ET)
Next action: 106
Actions raised at this meeting
No
Action
101
Semantics of 'fixed'
102
Clarify the specification of error reporting from a DFDL processor
- section 2.3 needs to be updated
103
Asserts and discriminators
- specify the scope of forward references. Must be downward-only. The
expression must be resolvable by the time the component on which it is
positioned goes out of scope - otherwise it is a processing error.
104
Expressions
Discuss error behaviour when evaluating an expression in various contexts
- All properties:
wrong type returned : schema definition error
exception when evaluating expression : schema definition error
referenced variables/paths not available : schema definition error
- Properties which allow a forward reference
referenced variables/paths not available : no error. DFDL processor
continues processing until the expression result is available, then acts
on the result.
105
Grammar for DFDL expression
- currently allows multiple predicates on a single expression. Sounds as
if this was unintended.
Current Actions:
No
Action
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
...
17/02: IBM is willing in principle to publish the test case format and
some of the test cases. May need some time to build a 'compliance suite'
24/03: No progress
03/03: Discussions have been taking place on the subset of tests that will
be provided.
10/03: work is progressing
17/03: work is progressing
31/03: work is progressing
14/04: And XML test case format has been defined and is being tested.
21/04. Schema for TDML defined. Need to define how this and the test cases
will be made public
05/05: Work still progressing
12/05: Work still progressing
02/06: Work still progressing on technical and legal considerations
...
14/07: work continues
085
ALL: publicize Public comments phase to ensure a good review..
14/04: see minutes
21/04: Press release, OMG and other standards bodies.
05/05: Alan and Steve H have contacted other standards bodies. Will ask
them to add comments on spec
15/05: still no public comments
02/06: No public comments
16/06: Public comments period has ended with no external comments. Alan
had posted changes made in draft 041. Steve suggested send a note to the
WG highlighting these changes. Steve also suggested requesting an
extension as other IBM groups may review. We discussed whether this was
necessary as changes will need to be made during the implementation phase
anyway. Alan to ask OGF what the process is for changes post public
comment.
23/06: Still no comments. Alan will contact OGF to understand the rest of
the process.
30/06: Alan has emailed Joel asking what the process is now public comment
period is over andcan we update the published version with WG updates. No
response yet.
07/07: No response. Alan will chase up
14/07: No response from Joel. Sent email to Greg Newby by no response.
086
AP: Nils and Defaults during unparsing - update table
31/03: TK to documetn use cases for parsing
14/04: Investigate new property to control empty string behaviour.
21/04: After investigation a new property is not required. New rules
developed and tables updated.
Need examples of complexTypes to confirm tables apply.
Review Nils, defaulting spec section.
05/05: Discussed defaulting complex elements. Tables updated but need to
add terminator.
SH; to confirm WMD behaviour when infoset item has no value on unparsing
Need to describe defaulting choices.
15/05: More discussion. Alan updating sections
26/05: Discussed draft updates. Stephanie to confirm asserts do not make
an element required.
Alan will update draft.. All: review rest of draft.
02/06: Alan updated description. Please review.
Discussed Stephanie's example using discriminators. Decided no changes
needed.
16/05: went through Steves comments. Steve to update draft.
23/06: Steve's updates to the rules discussed. See minutes. Rest of
document needs updating.
30/06: Discussed Alans updates. Some corrections. Alan will send out
updated copy for review before next call.
07/07: Discussed Alan updates and Tim and Steve's comments. Still some
corrections and updates.
14/07: Discussed Alan updates (v9) Still some corrections and updates.
099
Splitting the specification in simpler sections.
07/07: Steve sent a proposal but not discussed. Alan will arrange a
separate call.
14/07:Discussed Steve's proposal and Suman's and Alan's comments.
Need to add choice, validation, facets.
Also how does an implementation declare which subsets it supports.
Suggested levels and/or profiles. Steve highlighted a problem when a DFDL
schema from an implementation of just the core functions was moved to a
full DFDL implementation what should happen about the missing properties.
Does the full implementation need to be aware of subsets of functions?
Should it raise a schema definition error for use of a function not in the
subset.
101
Semantics of 'fixed'
102
Clarify the specification of error reporting from a DFDL processor
- section 2.3 needs to be updated
103
Asserts and discriminators
- specify the scope of forward references. Must be downward-only. The
expression must be resolvable by the time the component on which it is
positioned goes out of scope - otherwise it is a processing error.
104
Expressions
Discuss error behaviour when evaluating an expression in various contexts
- All properties:
wrong type returned : schema definition error
exception when evaluating expression : schema definition error
referenced variables/paths not available : schema definition error
- Properties which allow a forward reference
referenced variables/paths not available : no error. DFDL processor
continues processing until the expression result is available, then acts
on the result.
105
Grammar for DFDL expression
- currently allows multiple predicates on a single expression. Sounds as
if this was unintended.
Closed actions
No
Action
088
define semantics of choiceKind 'fixedLength'
31/03: TK to provide definition of calculable length.
Investigate PL/I varchars and Cobol occurs dependingon.
14/04Tim had distributed a document starting the definition of calculable
length for the longest choice member.
Alan had done some investigation of COBOL occurs depending on and when
used in the working section of a program then the maximum storage was
reserved but when used in the linkage section the dependent number was
uses. We need to understand how the WMB COBOL importer deals with ODO.
21/04: Need to define 'calculable length' and WMB importer ODO behaviour.
05/05: TK: Still need definition of calculable length.
SKK: WMB COBOL imported behaviour with ODO
15/05: Suman sent an expmle of an imported Cobol ODo which suggested that
the maximum space was reserved. He will extend the example.
02/06: no progress
16/06: no progress
23/06: no progress
30/06: Alan looked at Tim's description of calculable length and suggested
that that real use case may be much simpler. If real use case is COBOL and
C importers then it would be cleaner to require the 'fixed length' to be
specified on the enclosing complex element and remove choiceKind 'fixed
length'. Ask Suman is COBOL and C importers can be enhance to provide
length on cpmplex element.
07/07: Steve had proposed 5 possible approaches to supporting main use
case.
i) Change the importer to add a parent element for each group. Con: This
changes the logical model by inserting an extra level.
ii) Allow dfdl:length to be carried on embedded xs:choice (along with
dfdl:lengthUnits & dfdl:lengthKind).
iii) New dfdl:choiceLength property to be carried on embedded xs:choice
(always bytes).
iv) dfdl:choiceKind as today. Con: length from TD model is lost and must
be recalculated.
v) dfdl:choiceKind but with limitations to make the calculation easier.
Con: length from TD model is lost and must be recalculated.
Agreed a modified version of iii)
dfdl:choiceKind becomes dfdl:choiceLengthKind with emuns 'implicit'
(length of selected branch) and 'explicit' ( length specified by
dfd;choiceLength)
New property dfdl:choiceLength
14/07: Closed
096
AP: using textStringPadCharacter with charRef '%#r' on multi-byte encoding
14/07: Although there was some merit in having separate textPadKinds it
was felt it was too late to make the change. The property descriptions
(for numbers, calendars and booleans as well) will be improved. Closed
097
nilIndicatorPath and nilIndicatorIndex properties
07/07: Tim had emaled Mike with a proposal and Steve had responded with 3
alternatives
1) Leave things as they are, perhaps renaming 'nilIndicator' to
'indicator'
2) Collapse nilIndicatorPath and nilIndicatorIndex to a single property.
It means the path is repeated, but it makes nils consistent with length
and occurs. For all, you can always use a string variable to hold the
constant part of the path and concatenate with the index. And if we
improve usability in a future DFDL release, we would improve it for nils,
lengths and occurs at the same time.
3) Drop the properties for 1.0 altogether on the grounds that it is a rare
case. I've never seen such a format, but we know Mike has.
Not discussed.
14/07: As part of nils default discussion the WG decided to drop
dfdl:nilIndicator and dfdl:nilIndicatorIndex as it was felt the
complications it introduced on unparsing were not worth the additional
function. This may be revisited for DFDL v2.. Closed
100
Alignment enumerations when dfdl:lengthUnits = 'bits'
When alignmentUnits='bits', the rule that alignment must be 1,2,4,8 etc or
multiple of 2 looks rather hard to justify.
It was agreed to remove the restriction on aligmentUnits for both 'bytes'
and 'bits'. Closed
Work items:
No
Item
target version
status
005
Improvements on property descriptions
not started
012
Reordering the properties discussion: move representation earlier, improve
flow of topics
not started
036
Update dfdl schema with change properties
ongoing
042
Mapping of the DFDL infoset to XDM
none
not required for V1 specification
070
Write DFDL primer
071
Write test cases.
083
Implement RFC2116
105
AP: Describe trailingSkipBytes for delimited formats.
Alan suggested 'dfdl:terminator must be specified and not empty if
dfdl:lengthKind is delimited or endOfParent.'
106
AP: Skip Bytes should allow bits
Ageed that it should be possible to specify bits.
- LSB and TSB renames to dfdl:leadingSkip, dfdl:trailingSkip
- units are specified by dfdl:alignmentUnits.
107
Remove timing from dfdl:assert
108
AP: Confirm behaviour of defaulting with various occursCountKinds and
separator policies.
30/06: Decided that defaulting for variable occurrence arrays should
always be to minOccurs. If separatorPolicy is 'required' then just the
separators will be output up to maxOccurs and unbounded is an error.
109
define semantics of choiceKind 'fixedLength'
dfdl:choiceKind becomes dfdl:choiceLengthKind with emuns 'implicit'
(length of selected branch) and 'explicit' ( length specified by
dfd;choiceLength)
New property dfdl:choiceLength
110
nilIndicatorPath and nilIndicatorIndex properties
14/07: As part of nils default discussion the WG decided to drop
dfdl:nilIndicator and dfdl:nilIndicatorIndex
111
AP: using textStringPadCharacter with charRef '%#r' on multi-byte encoding
14/07: Although there was some merit in having separate textPadKinds it
was felt it was too late to make the change. The property descriptions
(for numbers, calendars and booleans as well) will be improved. Closed
112
Alignment enumerations when dfdl:lengthUnits = 'bits'
When alignmentUnits='bits', the rule that alignment must be 1,2,4,8 etc or
multiple of 2 looks rather hard to justify.
It was agreed to remove the restriction on aligmentUnits for both 'bytes'
and 'bits'. Closed
Regards
Alan Powell
Development - MQSeries, Message Broker, ESB
IBM Software Group, Application and Integration Middleware Software
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