Open Grid Forum: Data Format Description Language Working Group
OGF DFDL Working Group Calls, June 23-24 2009
These minutes cover the series of meetings and calls which took place June
23-24 2009
Meeting opened, 14:00 UK
Attendees
Steve Hanson (IBM)
Suman Kalia (IBM)
Alan Powell (IBM)
Peter Lambros (IBM)
Stephanie Fetzer(IBM)
Apologies
Mike Beckerle (Oco)
Agenda:
1. Go through actions
Actions updated below
Major discussions listed here.
Action 026 Envelopes and Payloads
Continued discussion of using variables to extract syntax from header but
also allowing body to be used stand alone.
Use cases expanded to :
1.Input -value of syntax item comes from header and is used in the body
2.Input -value of the syntax item is found in the header and is used in
the body but may change if the actual syntax used in the body changes
3.Input - no header. value of syntax item comes from first time used in
the body and must be one of a known set and doesn't change.
4.Input - no header, value of syntax item comes from first time used in
the body and may be changed if the actual syntax used in a following body
changes
5.Output - value of sytnax item set in header infoset and is used
throughout in the body
6 Output - no header.the default value syntax item is used throughout in
the body
We considered adding a 'dynamic' property to defineVariable to show that
if unset when first used the value should be taken from the data. However
it was felt that this may be unnecessarily complicated.
Alternatively allowing syntax properties to be a list satisfies most of
the use cases. SH to document.
Action 042 Variables.
The uses cases for variables refined to
Variable markup - set once from document content (typically near start of
document)
Variable markup - set (possibly multiple times) based on first usage (eg
first instance of separator determines separator character used)
Values set externally - eg encoding, byteorder
Parameterization of global entity - parameter set as fixed value or as
expression
Envelope/payload - payload markup/discriminator set by value(s) in
envelope
And the following aspects need to be defined
Scoping of defineVariable
naming/namespaces - include/import
Unparsing
Variable Type - enums
Multiple setVariables in loops etc
SKK had refined his proposal to allow defineVariable at schema,
defineFormat and locally which are analogous to Java global static,
private static and local variables. SKK also felt it would be difficult
for a dfdl editor to show which variables were available at particular
elements. However the rest of the group did not think that the extra
complication was needed for the defined use cases.
It was proposed that
defineVariable is at schema level only and are global. (though need to go
through uses cases to see if local needed also).
Variables are name space qualified
Variables can be set multiple times (needed for parameterization)
PL to document
Action 051 Scoping rules.
New lexical scoping rules need to cover
How parameterization works
Global simple types
dfdl;hidden
We went through examples of using variables for parameterization and it
seemed to hang together although the scope of variables meant that the
scope of parameters was different from scoping for properties.
To simplify the validation of global simple types it is proposed that
there are no dfdl annotaions on simple types. The unit of reuse is a
global element.
Hidden fields must be defined in a global group declaration. This must be
valid but this can be achieved by adding a ref to the same defineFormat
as the parent complexType. Tooling could do the 'automatically' when
fields are hidden.
The MB presentation will be updated to include these proposals.
Action Unresolvable choices.
It has been agreed to defer unresolvable choices from DFDL V1
Action 052 Discriminator Timing
Currently disciminator timing is implictly 'after' which means that a
component will be parsed before the discriminator is evaluated. However
that means that a parsing failure of the component will cause speculative
parsing to backtrack even though the discriminator might have evaluated
to true and fixed the point of uncertainty. We need to add a timing
property to discriminator so that it can be evaluated before parsing when
the content of the component is not needed for the evaluation.
Action 053 XPATH position() function
Use cases of arrays of existence flags or field lengths would be
simplified is there was a position() function
<xs:element name="size" type="xs:int"
dfdl:lengthKind="explicit" dfdl:length="4"/>
<xs:element name="len" type="xs:int" maxOccurs="unbounded"
dfdl:occursKind="explicit" dfdl:occursCount="{../size}"
dfdl:lengthKind="explicit" dfdl:length="4"/>
<xs:element name="image" type="xs:hexBinary" maxOccurs="unbounded"
dfdl:occursKind="explicit" dfdl:occursCount="{../size}"
dfdl:lengthKind="explicit" dfdl:length="{../len[fn:position()]}"/>
This implies that a context is maintained while navigating arrays and the
expression is evaluated for every occurrence of a element.
Agreed to add poistion()
AOB
Note: we can only make one call next week
Next call 1st July 14:00 UK Scheduled for 2 hours
Meeting closed, 16:00 UK
Actions raised at this meeting
No
Action
052
Discriminator timing property
24/06: Need to add timing property to discriminator
053
poistion() function
24/06: agreed to add
Current Actions:
No
Action
012
AP/SH: Update decimalCalendarScheme
10/9: Not allocated yet
17/9: No update
24/9: Add calendar binary formats to actions
22/10: No progress
16/1: proposal distributed and discussed. Will be redistributed
21/1: add locale,
04/02: changed from locale to specific properties
18/2: Need more investigation of ICU strict/lax behaviour.
08/04: Not discussed
22/04: AP to complete asap once the ICU strict/lax behaviour is
understood.
29/04: No progress
06/05: No progress
13/05: Calendar has been added to latest spec version v034 but still a few
details to clarify.
20/05: No Progress
27/05: No Progress
03/06: No Progress (low priority)
09/06: No Progress (low priority)
17/06: SH to check ICU code for lax calendar behaviour
24/06: no progress
026
SH: Envelopes and Payloads
08/04: Not discussed explicity, but recursive use of DFDL is tied up with
this
22/04: Two aspects. Firstly compositional - do sufficient mechanisms exist
to model an envelope with a payload that varies. Secondly markup syntax -
this might be defined in the envelope.
The second of these is very much tied up with the variable markup action
028, so will be considered there. SH to verify the composition aspect.
29/04: SH and AP working on proposal. related to Action 028
06/05: No progress
06/05: No progress
20/05: No Progress
27/05: Still a number of aspects to be decided.
- Compostion - Does the envelope and payload need to be defined in the
same schema or should they be dynamically bound at runtime?
- Compostion- How is a variable payload specified. Choice or xs:any; New
action raised to discuss xs:any
- extracting dymanic syntax from data. Covered by action 029 valuecalc.
03/06: Dynamic runtime binding will not be supported.
SH investigating use of variables to enable standalone and use in envelope
of global element.
09/06: Payload should be specified using a choice rather than xs:any
17/06: SH still working on example using variables
24/06: SH to document how property list satisfies uses cases.
027
SH: Property precedence tables
08/04: Not discussed
22/04: Two things missing from the existing precedence trees. Firstly,
does not show alternates (eg, initiator v initiatorkind). Secondly, need a
tree per concrete DFDL object (eg, element). SH to update.
29/04: No progress
06/05: SH is updating tables which will be ready for next call
13/05: SH emailed updated version. AP commented.. See minutes for issues
and property changes.
20/05: Updated version circulated. Review before next call and be ready
for vote.
27/05: Updated version circulated. more comments raised.
03/06: Further updates to clarify 'core'. Also identified missing design
for outputMinLength
17/06: Being updated to include outputMinlength
24/06: Table now in maintenance mode. Move to work item
029
MB: valueCalc (output length calculation)
08/04: Not discussed
22/04: Action allocated to MB, this is to complete the work started at the
Hursley WG F2F meeting.
29/04: No progress
06/05: MB will have update for next call
13/05: MB will have update for next call
20/05: Some progress. will be circulated this week
27/05: MB circulated proposal and got comments. Will update and review on
next call
03/06: Discussed proposal. MB to update dealing with uses cases raised.
Options include a new lenghtKind='Reference' to make it easier to
distinguish from fixed length case. Or use outputLengthCalc to separate
calculation of parsing and unparsing length.
09/06: SH/AP proposal discussed and MB to document
17/06: MB to document proposal.
Grammar updated and reviewed. Minor changes needed.
24/06: Grammar description was updated and approved. Need to describe new
function.
033
AP/TK: Assert/Discriminator semantics. AP to document. TK to check uses of
discriminator besides choice.
08/04: In progress within IBM
22/04: Waiting for TK to return from leave to complete.
29/04: TK has sent examples shown need for discriminators beyond choice.
Agreed. MB to respond to TK
06/05: Discussed suggestion of adding type indicator to discriminator. MB
to provide examples.
15/03: Semantic documented in v034. MB to provide examples of need for
scope indicator on discriminator
20/05: MB to provide examples of need for scope indicator on discriminator
(but lower priority than action 029)
27/05: No Progress (lower priority)
03/06: No Progress (lower priority)
09/06: No Progress (lower priority)
24/06: No Progress (lower priority)
037
All: Approach for XML Schema 1.0 UPA checks.
22/04: Several non-XML models, when expressed in their most obvious DFDL
Schema form, would fail XML Schema 1.0 Unique Particle Attribution checks
that police model ambiguity. And even re-jigging the model sometimes
fails to fix this. Note this is equally applicable to XMl Schema 1.1 and
1.0. While the DFDL parser/unparser can happily resolve the ambiguities,
the issue is one of definition. If an XSD editor that implements UPA
checks is used to create DFDL Schema, then errors will be flagged. DFDL
may have to adopt the position that:
a)DFDL parser/unparser will not implement some/all UPA checks (exact
checks tbd)
b) XML Schema editors that implement UPA checks will not be suitable for
all DFDL models
c) If DFDL annotations are removed, the resulting pure XSD will not always
be valid (ie, the equivalent XML is ambiguous and can't be modelled by XML
Schema 1.0)
Ongoing in case another solution can be found.
29/04: Will ask DG and S Gao for opinion before closing
06/05: Discussed S Gao email and suggestions. Decided need to review all
XML UPA rules and decide which apply to dfdl.
20/05: SH or SKK to investigate
27/05: No Progress
03/06: The concern is that some dfdl schemas will fail UPA check when
validation is turned on or when editted using tooling that enforces UPA
checks. Renaming fields will resolve some/most issues. Need documentation
that describes issue and best practice.
17/06: no change
24/06: no change
038
MB: Submit response to OMG RFI for non-XML standardization
22/04: First step is for MB to mail the OGF Data Area chair to say that we
want to submit
29/04: MB has been in contact with OMG and will sunbit dfdl.
06/05: MB has prepared response to OMG. Will send DFDL sepc v033
20/05: Response has been sent to OMG based on v034
27/05: Awaiting response from OMG.
03/06: On hold
042
MB: Complete variable specification.
To include how properties such as encoding can be set externally. Must be
a known variable name.
06/05: No progress
20/05: AP to make proposal
27/05: MB proposed differentiating between input and output variables to
avoid unnecessary evaluations during parse and unparse. Need to complete
rest of variable specification.
03/06: Pointed out problem of declaring variables input or output when
used to define syntax which is used both times. MB to update proposal to
include how variables are set externally and how specific properties such
as encoding are set.
09/06: SKK to use example to dicument his proposal
17/06: SKK to refine proposal. Other aspects need progress.
24/06: SKK proposal discussed but not accepted. PL to document simpler
proposal.
044
13/05: Bidi
20/05: AP: will check what IBM products support.
27/05: Bidi is supported so will be needed in dfdl v1
03/06: No Progress
09/06: No Progress
24/06: No Progress
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
049
20/05 AP Built-in specification description and schemas
03/06: not discussed
24/06: No Progress
051
Scoping rules.
MB: to document change to scoping rules to satisfy implementation concerns
17/06: MB and SH proposals discussed. Needs further discussion
24/06: AP to update presentation with latest proosal
052
Discriminator timing property
24/06: Need to add timing property to discriminator
053
poistion() function
24/06: agreed to add
Closed actions:
028
SH: Variable markup
08/04: Discussed briefly at end of call, IBM to see whether there any use
cases that require recursive use of DFDL.
15/04: Use case was distributed and will be discussed on next call.
22/04: The use case in question is EDI where the terminating markup for
the payload segments is defined in the ISA envelope segment. The markup is
modelled as an element of simple type where the allowable markup values
are defined as enums on the type. But we need to handle two cases -
firstly where the envelope is present, so the value used by the payload is
taken from the envelope. Secondly where only the payload is present. Here
we need a way of scanning for all the enum values, and adopting the one we
actually find, when parsing. And using a default when unparsing. SH to
explore use of a DFDL variable, where the variable has a default, but also
has a type that is the same as the markup element - that way we get to use
the enums without defining everything twice.
29/04: SH and AP working on proposal.
06/05: No progress
13/05: No progress
20/05: No Progress
27/05: Progress made and will tie to other actions
03/06: General desire to avoid having to introduce variable markup in V1.
Proposed having a property to control case behaviour of all syntax
(initiator, terminator,separator) rather than separate ones for each.
Similar property to 'values' (textZeroRep, textBooleanTrueRep, etc). and
allowing lists of values. SH need to solve remaining uses case as
described in action 026
09/06: SH proposal discussed. ICU questions to be researched
17/06: ICU is always case insensitive. SH to update proposal.
24/06 Recursive use of dfdl will not be supported in dfdl v1 (except for
prefixlengthType). Closed.
050
27/05: xs:any currently limited to initiated text element. Is this
sufficient? Should xs:any in its current form be deferred?
03/06: not discussed
09/06: Proposed dropping xs:any support
17:06: Agreed to defer from DFDL v1 subject to final checks that IBM do
not need function.
24/06: Not needed by IBM. Closed
Work items:
No
Item
target version
status
003
Variables - ??, 2008 (Mike)
005
Improvements on property descriptions - ??, 2008 (All - split TBD)
006
Envelopes and Payloads (Steve) - Apr 30, 2008
007
(from draft 32) valueCalc (Mike) - ??, 2008
mostly
complete
008
(from draft 32) Property precedence for writing (Steve) -
under review
009
(from draft 32) Variable markup (Steve) - Mar 31, 2008
proposal needs writing up
011
(from draft 32) How speculative parsing works (combining choice and
variable-occurence - currently these are separate) ??, 2008 (IBM)
in progress
012
(from draft 32) Reordering the properties discussion: move representation
earlier, improve flow of topics ??, 2008 (Alan)
not started
027
Calendar schemes
034
032
Floating components
033
Changes from action 020 and 027 - renaming properties etc
035
Remove unorderedInitiated, add initiated content (a041)
036
Update dfdl schema with change properties (Suman)
037
Infoset text codepage
038
Improve length section
039
Change scoping of simple types (A 046)
040
Document outputMinLength (A027)
042
mapping of the dfdl infoset to XDM
Not required for V1 specification
043
Document infoset data types (A043)
044
non-format scoping rules (A047)
045
Defer unresolvable choice.
046
Document properties for syntax ignore case, etc alternative to variable
markup
047
Remove xs:any
Alan Powell
MP 211, IBM UK Labs, Hursley, Winchester, SO21 2JN, England
Notes Id: Alan Powell/UK/IBM email: alan_powell(a)uk.ibm.com
Tel: +44 (0)1962 815073 Fax: +44 (0)1962 816898
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