Open Grid Forum: Data Format Description Language Working Group
OGF DFDL Working Group Call, August 04-2010
Attendees
Steve Hanson (IBM)
Alan Powell (IBM)
Stephanie Fetzer (IBM)
Ella Belisario (IBM)
Apologies
Mike Beckerle (Oco)
Suman Kalia (IBM)
Tim Kimber(IBM)
1. Current Actions
Updated Below
2. dfdl:hidden
There has been some discussion on whether the 'hidden' global group should
be indicated in some way.
Option A:
Leave the DFDL specification unchanged, in which case we must expose the
internal DFDL constructs to the user of the DFDL editor. That means the
following:
- to make a group member hidden, a local group and a global group must be
created to represent the hidden item. This is a refactoring operation.
- to make the UI consistent, the global group needs to be exposed as a
first-class modelling construct. That means that it appears along with
local element/element ref/local group/group ref in any context where the
user is dealing with group members.
There are more details of what the editor needs to do in Steve's comments
on the first note in this chain.
Option B:
Make one change to the DFDL specification, to make it possible for a DFDL
editor to present dfdl:hidden as a simple flag on any group member
The change is to put a DFDL annotation on the global sequence group that
contains the hidden items. This would allow the DFDL editor to distinguish
these global groups from the real ones that belong to the user's schema.
This allows a hidden item to be represented by a pair of *internal*
groups, both of which have a dfdl:annotation. One is local, and appears
where the hidden item used to appear, The other is global and is
referenced by the local one. They are created and deleted as pairs
whenever an item is hidden or un-hidden.
A lively discussion. The specification works as currently defined so
discussed whether changes need to be made to make tooling easier. There
shouldn't be 'conventions' in particular tooling as they must be able to
properly deal with schema from other tools that would not obey those
conventions. Steve stated that it is often dangerous to hide too much from
users when they can see they underlying schema. To be continued.
3. dfdl:discriminator : the 'message' attribute
>From Tim:
I remembered the reason why I thought this was a good idea.
Consider the situation where someone is generating their DFDL schema from
meta-data. The model is large, and consists of many references to global
structures. Each global structure ( e.g. an HL7 segment ) is identified in
a particular way. Sometimes the segment is required, sometimes it is not.
Sometimes it occurs as a child of a choice group, and sometimes not.
Regardless, it is highly likely that the segment will be identified in the
same way wherever it occurs. A natural decision for the modeler would be
to create a dfdl:discriminator on all references to the segement, even if
the ref is not under a point of uncertainty. It's harmless, and it carries
no performance penalty. If we disallow the "message" attribute, it will
force the modeler to put in extra logic to work out whether the ref is
under a POI, and generate an assert/discriminator as appropriate.
I'd be interested to know what Steph thinks about this - I think I've
heard her say that she sometimes uses discriminators where an assert would
have done the job, just to maintain consistency throughout the model.
04/08: not discussed.
Meeting closed, 16:00
Next call Wednesday 11 August 2010 15:00 UK (10:00 ET)
Next action: 110
Actions raised at this meeting
No
Action
108
dfdl:hidden
There has been some discussion on whether the 'hidden' global group should
be indicated in some way.
04/08: A lively discussion. The specification is works as currently
defined so whether changes need to be made to make tooling easier. There
shouldn't be 'conventions' in particular tooling as they must be able to
properly deal with schema from other tools that would not obey those
conventions. Steve stated that it is often dangerous to hide too much from
users when they can see they underlying schema. To be continued.
109
dfdl:discriminator : the 'message' attribute
>From Tim:
I remembered the reason why I thought this was a good idea.
Consider the situation where someone is generating their DFDL schema from
meta-data. The model is large, and consists of many references to global
structures. Each global structure ( e.g. an HL7 segment ) is identified in
a particular way. Sometimes the segment is required, sometimes it is not.
Sometimes it occurs as a child of a choice group, and sometimes not.
Regardless, it is highly likely that the segment will be identified in the
same way wherever it occurs. A natural decision for the modeler would be
to create a dfdl:discriminator on all references to the segement, even if
the ref is not under a point of uncertainty. It's harmless, and it carries
no performance penalty. If we disallow the "message" attribute, it will
force the modeler to put in extra logic to work out whether the ref is
under a POI, and generate an assert/discriminator as appropriate.
I'd be interested to know what Steph thinks about this - I think I've
heard her say that she sometimes uses discriminators where an assert would
have done the job, just to maintain consistency throughout the model.
04/08: not discussed.
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
...
21/07: work continues
04/08: 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.
21/07: Still no response.
04/08: Joel has responded that it is up to the WG to decide if the changes
are significant enough to need additional review. Alan to contact David
Martin and Erwin Laure for guidance if we split the specification.
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.
21/07: no progress
04/08: Steve had updated proposed groups of function.
(Subset_proposal_v2.ppt). We discussed whether its is better to have
discrete sets of functions or expanding levels of function.
Purpose of subsetting is:
1. Allow simpler implementations. (main purpose)
2. Simplify tooling
3. Simplify specification.
Steve to contact previous members of WG to check if we have the correct
subsets.
101
Semantics of 'fixed'
21/07: Discussed whether not matching the 'fixed' value should be a
validation error or processing error. Decided that for consistency it
should be a validation error.
It would be useful however to avoid having to duplication of facet
information in an assert which could become unwieldy for, say, a large
enumeration.
Suggestions
- a parser option that 'converted all validation errors to porcessing
errors'
- a dfdl expression function that 'applied all facets' or 'applied
specific facet' to a particular element.
Stephanie will produce some examples of how this could be used..
04/08: Stephanie had produced examples but they were not discussed due to
lack of time
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.
21/07: Steve stated the current definition that returning the incorrect
type was a schema definition error and everything else was a processing
error.
04/08: Not discussed
107
teston/testoff dfdl expression functions.
Are these functions still needed. They were introduced to allow individual
bits to be set in a byte. Steve to look at TLog and ISO 8583 formats that
use existence flags to see if they are still required.
04/08: Not discussed
108
dfdl:hidden
There has been some discussion on whether the 'hidden' global group should
be indicated in some way.
04/08: A lively discussion. The specification is works as currently
defined so whether changes need to be made to make tooling easier. There
shouldn't be 'conventions' in particular tooling as they must be able to
properly deal with schema from other tools that would not obey those
conventions. Steve stated that it is often dangerous to hide too much from
users when they can see they underlying schema. To be continued.
109
dfdl:discriminator : the 'message' attribute
>From Tim:
I remembered the reason why I thought this was a good idea.
Consider the situation where someone is generating their DFDL schema from
meta-data. The model is large, and consists of many references to global
structures. Each global structure ( e.g. an HL7 segment ) is identified in
a particular way. Sometimes the segment is required, sometimes it is not.
Sometimes it occurs as a child of a choice group, and sometimes not.
Regardless, it is highly likely that the segment will be identified in the
same way wherever it occurs. A natural decision for the modeler would be
to create a dfdl:discriminator on all references to the segement, even if
the ref is not under a point of uncertainty. It's harmless, and it carries
no performance penalty. If we disallow the "message" attribute, it will
force the modeler to put in extra logic to work out whether the ref is
under a POI, and generate an assert/discriminator as appropriate.
I'd be interested to know what Steph thinks about this - I think I've
heard her say that she sometimes uses discriminators where an assert would
have done the job, just to maintain consistency throughout the model.
04/08: not discussed.
Closed actions
No
Action
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.
21/07: Discussed Draft 10. Shouldn't mention input/outputValueCalc in this
section. Mention defaulting in calculated values section.
Move details of nilValue from nilKind property.
04/08: Draft v11.1 was included in Spec Draft v42. Minor corrections.
Closed.
102
Clarify the specification of error reporting from a DFDL processor
- section 2.3 needs to be updated
21/07: Section is not clear. Alan will update.
04/08: Sections updated in draft 42. Closed
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.
21/07: Agreed
04/08: Updated in draft 42. 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
Regards
Alan Powell
Development - MQSeries, Message Broker, ESB
IBM Software Group, Application and Integration Middleware Software
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