[DFDL-WG] Minutes for OGF DFDL Working Group Call, September 15-2010
Alan Powell
alan_powell at uk.ibm.com
Fri Sep 17 04:57:46 CDT 2010
Open Grid Forum: Data Format Description Language Working Group
OGF DFDL Working Group Call, September 15-2010
Attendees
Stephanie Fetzer (IBM)
Steve Hanson (IBM)
Bob McGrath (National Center for Supercomputing Applications)
Alan Powell (IBM)
Tim Kimber(IBM)
Alejandro Rodriguez (National Center for Supercomputing Applications)
Apologies
Mike Beckerle (Oco)
Suman Kalia (IBM)
1. Current Actions
Updated Below
Action 099 Proposed optional properties
Feature
Detection
Pre-reqs
NCSA ?
Comments
Validation
External switch
None, but of limited value without Simple type restrictions
No
Simple type restrictions
xs:simpleType in xsd
None
No
Nils
xs:nillable='yes' in xsd
None
No
Defaults
xs:default or xs:fixed in xsd
None
No
Bi-di
dfdl:textBiDi='yes'
None
No
Bits
dfdl:alignmentUnits='bits' or dfdl:lengthUnits='bits'
None
No
Delimited binary
dfdl:representation='binary' (or implied binary) and
dfdl:lengthKind='delimited'
None
No
Patterns
dfdl:lengthKind='pattern' or dfdl:assert testPattern
None
Yes
Zoned numbers
dfdl:textNumberRep='zoned'
None
No
z/OS
Packed numbers
dfdl:binaryNumberRep='packed'
None
Yes
z/OS
Packed calendars
dfdl:binaryCalendarRep='packed'
None
z/OS
S/390 floats
dfdl:binaryFloatRep='ibm390Hex'
None
No
z/OS
Unordered
dfdl:sequenceKind='unordered'
None
Not clear
Floating
dfdl:floating='yes'
None
No
dfdl functions in expression language
dfdl: functions in expression
None
No
Enables use of off-the-shelf XPath 2.0 package
Hidden
dfdl:hiddenRef <> ''
None
Yes
Calculated values
dfdl:inputValueCalc <> '' or dfdl:outputValueCalc <> ''
None
Yes
Escape schemes
dfd;defineEscapeScheme in xsd
None
Yes
Encodings
Any dfdl:encoding value beyond the core list
None
Not clear
Asserts
dfdl:assert in xsd
None
Yes
Discriminators
dfdl:discriminator in xsd
None
Yes
Prefixed lengths
dfdl:lengthKind='prefixed'
Simple type restrictions
Not clear
Requires simple types
Variables
Variables in
expression
language
None
Yes
2. Document that an empty sequence that is the content of complex type is
ignored even when it has annotations
One thing to point out is that the authors should avoid
<xs:complexType>
<xs:sequence dfdl:hiddenGroupRef="..."/>
</xs:complexType>
(The same applies to other annotations on sequences, long- or short-form.)
The schema spec will discard that sequence (see [1] definition of
"effective content" clause 2.1.2). The following works:
<xs:complexType>
<xs:sequence>
<xs:sequence dfdl:hiddenGroupRef="..."/>
</xs:sequence>
</xs:complexType>
[1] http://www.w3.org/TR/2004/REC-xmlschema-1-20041028/#key-exg
It is a schema definition error if an empty sequence is the content of a
complex type
Meeting closed, 16:35
Next call Wednesday 22 September 2010 15:00 UK (10:00 ET)
Next action: 118
Actions raised at this meeting
No
Action
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
...
25/08: Will chase to allow Daffodil access to test cases. The WG should
define how implementation confirm that they 'conform to DFDL v1'
01/09: IBM still progressing the legal aspect. Intends to publish 100 or
so tests as soon as it can, ahead of a full compliance suite.
08/09: IBM still progressing
15/09: IBM still progressing, expect tests to be available within a few
weeks
085
ALL: publicise 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 and can 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.
11/08: Received a response from Joel that the WG can decide if a re-
public review is necessary before becoming a 'proposed recommendation'.
Alan responded that the WG agreed that a re-review was not necessary. The
next stage is for OGF review committee to approve publication.
11/08: Specification is now 'awaiting author changes' before being
submitted to the OGF technical committee for approval as a 'proposed
specification'.
Alan would like to have the updated specification complete by Sept 10th.
The WG needs to complete all actions by then or decide that they do not
need to be included in this phase of the process.
01/09: Alan and Steve have discussed and propose Sept 30th for completion
of draft 43 and closure of all actions.
08/09: Target for completion September 30.
15/09: as above
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
11/08: Steve sent an email to previous members of the WG asking for
opinions on splitting the specification. Bob McGrath from National Center
For Supercomputing responded that they had implemented about 80% of the
function. Alejandro will send a description of the function they have
implemented.
Action will be raised to track the Daffodil implementation
11/08: not discussed
01/09: NCSA implementation description received. Making the unparser
optional is a good idea (NCSA do not need one) . Work will progress on the
subsets.
08/09: No progress
15/09: Steve proposed making 'obscure' properties optional rather than
subsetting parts of the specification. See minutes for proposed list of
optional properties.
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 processing
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
11/08: We started to discuss Stephanie's HIPPA example but ran out of
time.
25/08: Not discussed
01/09: Discuss next week
08/09: Stephanie sent an example of an X12 document showing how an element
with the same name was defined in different groups with different
enumerations.
Proposal:
- xs:fixed will not be used for parsing but only for validation and for
providing a default value on unparsing.
- A new dfdl function will be defined that applies only to simple element
and tests whether the element exists including applying all the schema
facets. (need to check with Tim why he wanted to only apply enumerations)
dfdl:exists( xpath , true ¦ false) true means apply facets, false means
don'e apply facets.
<xs:element
ref="REF_BillingProviderTaxIdentification_2010AA">
<xs:annotation>
<xs:documentation>Discrimination needed to distinguish REF
segments</xs:documentation>
<xs:appinfo source="
http://www.ogf.org/dfdl/">
<dfdl:discriminator
test="{dfdl:exists(./REF01__ReferenceIdentificationQualifier, true)}"/>
</xs:appinfo>
</xs:annotation>
15/09: Decided that a separate dfdl:checkConstraints (or other suitable
name) function, that checks all constraints not just facets, was simpler
than extending fn:exists. It applies to both simple and complex element
and to groups
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
11/08: Not discussed
25/08: Not discussed
01/09: Steve to progress by Sept 30th
08/09: Steve to progress by Sept 30th
15/09: The ISO 8583 standard has existence flags at the beginning that are
encoded so cannot be defined as an array of bits. Therefore DFDL needs the
ability to set individual bits within an unsigned int. However the
functions, particualry SetOn/Off, as currently defined are not correct.
SetOn returns a byte with the relevant bit set on. This must then be
combined with other bytes which isn't very usable. Steve to circulate
example of use and suggested improvements.
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.
25/08: there has been some offline discussions about simplifying how
hidden elements are implemented. The proposal is
dfdl:hidden property on xs:element only
xs:minOccurs and xs:maxOccurs MUST be 0 when hidden
dfdl:minOccurs and dfdl:maxOccurs for hidden elements only.
An element is 'required' when dfdl:minOccurs >0 and normal default
processing occurs.
The schema, without dfdl annotations, must match the infoset so
assumption is that non-DFDL tools, such as mappers, will ignore/not show
elements with xs:minOccurs and xs:maxOccurs = '0'
01/09: The above proposal is flawed due to use of maxOccurs = 0 (this was
identified back in 2008 hence current spec).
Bob confirmed that NCSA models use hidden in a big way, so punting hidden
beyond 1.0 is not an option.
Two candidates:
- As per spec but with syntactic improvements to make it clear that the
two xs:sequences do not take any dfdl:sequence properties
- Place a flag directly on a local element and force minOccurs to be 0.
Simpler syntax but the semantic changes, as the element *could* be legally
in the infoset, although a DFDL parser would never put it there.
Steve will circulate the two proposals for next week.
Bob to talk to Alejandro as the NCSA implementation is currently more
flexible than the spec, allowing the groupref to point to a choice, and an
elementref. Are these really needed?
08/09: Discussed the Global Group and Hidden Flag approaches.
Decided to stay with Global Group with dfdl:sequence properties rather
than the dfdl:hidden annotation. It was agreed that there would be no
extra properties on the 'hidden' global group as the syntax was messy as
it should really be on the sequence and there are currently no dfdl
properties on global groups.
Global group approach
Summary:
Particle to hide can be a local element, element ref, local sequence,
local choice or group ref
Particle is removed from its parent into a dedicated global group of
composition sequence and replaced in the parent by a new empty local
sequence
The new empty local sequence carries a dfdl:hiddenGroupRef property, other
DFDL properties are not allowed
Pros:
Removal of all DFDL annotations and use of the resultant pure XSD results
in same infoset
Global group can be reused
Cons:
Making something hidden is a refactor operation
Global group sequence needs DFDL properties setting correctly
The Daffodil parser allows the hidden annotation to reference global
elements in addition to global groups. It was noted that this lost the
particle properties but we need to discuss with Alejandro.
15/09: Alan circulated section describing Hidden Sequence Groups. Noted
that hidden is now only described in the sequence sections of the
specficiation.
Noted some editorial changes.
Alejandro had implemented extensions to the hidden function.
1. Allow hidden sequence to reference a global element. Decided against as
Suman had identified some problems with namesapces.
2. Allow the reference global group to contain a choice in addition to a
sequence. It was agreed this was a useful extension.
111
Daffodil DFDL parser
11/08: Bob and Alejandro described the new implementation that they have
developed. It is a new code base and is not based on the Deffudle
prototype. It is written in scala and implements approximately 80% of the
features in the public comments draft of DFDL V1. Alejandro will send a
list of the features not implemented.
We discussed the scenarios that motivated the development which was to
extract data from various sources and transform into canonical formats.
Bob offered to make Daffodil available for the WG to assess the
functionality. IBM WG members will get approval the company to allow them
to receive Daffodil.
Bob raised the question that if Daffodil becomes the public implementation
of DFDL then we will need to work out how that would be funded and
managed.
It would be helpful if IBM test cases were available to Daffodil. IBM will
investigate
25/08: Alejandro had sent a list of the functions that he has implemented
and Steve ahd responding indicating the extra functions he thought were
essential.
Since then Alejandro has implemented some of the missing functions, such
as escape schemes, pre-defined variables, binary decimal numbers, etc, and
will update his list.
Bob is planning to make the parser available on the internet to allow
testing.
His organisation is being reorganised and he doesn't know what the
priority of Daffodill will be so it is essential that we move quickly. It
would help if IBM could indicate its support for Daffodil in some
semi-formal way.
01/09: Alejandro updating Daffodil to include escape schemes, unordered
sequences and ignoreCase.
Daffodil being placed under formal source control in anticipation of
external release.
Bob has a start October deadline to create a report on what has been done
for his sponsors.
It would be great if we could get Daffodil on the web and have run some
IBM tests so it could be highlighted at OGF 30 at end October.
08/09: Alejandro is marking up Spec draft 42 to indicate which features
Daffodil implement. Bob expects Daffodil to be available on the web soon.
15/09: Alejandro had indicated in the specification which functions were
implemented in Daffodill. Steve had reviewed and identified which function
need to be implemented and which could be considered optional (see action
099). Alejandro is implementing the missing core functions. There was some
discussion about the limitations on unordered groups. (stop value and
expression not supported). It was agreed that it should be a schema
definition error if dfdl:occursCountKind is 'stopValue' on any element
within an unordered sequence and a floating element.
112
DFDL certification process
25/08: Discussed how to certify DFDL implementations. Alan to investigate
if OGF have a defined process.
01/09: In progress, spec needs to state what conformance means, as part of
this work
08/09: Discussed what needs to be said in the spec and agreed that details
of a conformance test suite should be in another document.
Alan to draft conformance section.
15/09: Alan had look at the conformance sections in XML and Schema
specifications both of which indicate sections which must be implemented.
None just say 'execute the test suite'. They talk in terms of conformance
of document, schema and processors..
113
Regular Expressions.
25/08: The DFDL regular expressions should provide lookahead and
backreferences. Is the current regular expression language sufficient?
a. Is the XML regular expression language the correct one to use. Tim
asked if DFDL needs to specify an language at all and should leave it to
implementers to pick one. That would inhibit portability of schema.
01/09: There are many variations of regexp language, it seems wise to
specify one that we know contains functions like lookaround, which makes
it easy to say things like 'give me everything up to but not including x'.
This rules out XML Schema and POSIX, it needs Perl 5 or Java.
08/09: Agreed that specification should define the regular expression
language (if only by referring to other specifications) .
Should allow a common subset of PERL and Java expressions languages. Alan
to update regular expression section.
15/09: Agreed that should just say that either JAva or PERL regular
expressions can be used and for portability the common subset of
functions should be used.
113b
Regular Expressions for Assert/Discriminator.
25/08: The DFDL regular expressions should provide lookahead and
backreferences. Is the current regular expression language sufficient?
b. A regular expression property on an assert/discriminator as an
alternative to the test expression. Either a DFDL expression or a regular
expression could be specified but not both.
01/09: Tim to convince Steve (via example) that use of regexp in asserts
is needed in 1.0.
08/09: Agreed that this is a useful function
Allowed as alternative to expression on dfdl:assert and dfdl:discriminator
Pattern may be specified as attribute or element value
Attribute: new testPattern attribute
Element value: braces ( ) indicate pattern instead of expression
15/09: Do not need the braces as expressions start with '{'. Need to state
rules for where the patter matching starts in the data stream.
114
OGF 30
25/08: OGF30 takes place on October 25-29 in Brussels. Should we have a
WG session?
09/01: Given emergence of NCSA implementation and spec completion target
of 30th Sept it makes sense to host a session at OGF 30.
08/09: Steve to request permission to go
15/09: Travel request has be submitted
115
Clarify allowed lengths for signed integer types when rep is binary
integer (ie, two's complement)
01/09: No technical reason to restrict lengths to 2^x bytes, could be odd,
could be bits. But rare in practise so if we do relax, limit any core
subset to 2^x bytes.
08/09: not discussed
15/09: not discussed
Closed actions
No
Action
117
3. Is UTF-16 a fixed width or variable width encoding
Appendix A: About UTF-16 and Unicode Character Codes above 0xFFFF
When we define UTF-16 to be a fixed-width double-byte wide character set
we say that each UTF-16 codepoint is represented by 2 bytes. Notice the
careful use of the term 'codepoint' here. Unicode/ISO10646 characters can
have character codes as large as 0x10FFFF which requires 3 bytes to store
(21 bits actually); however in UTF-16 characters with more than 2 bytes of
code are encoded as two codepoints, called a surrogate pair; hence, UTF-16
is fixed-width, 2 bytes per codepoint. It is not 2 bytes per Unicode
character. UTF-16 is really a variable-width encoding, but the characters
that require the surrogate-pair treatment are so infrequently used that
UTF-16 is most often treated like a 16-bit fixed-width character set. It
is the acknowledgement of the existence of surrogate pairs that leads to
the ?codepoint? vs. ?character code? distinction.
UTF-32 is a fixed width encoding with a full 4-bytes per character code.
It represents all of Unicode with the same width per character.
Hence, when we refer to lengths in character strings we will often refer
to length in characters, but we qualify that it means 2-byte codepoints
when the character set encoding is UTF-16. Hence, when the property
lengthUnitKind is 'characters' and the charset is 'UTF-16', then the units
are actually 16-bit codepoints, not Unicode characters.
Proposal
-UCS2 is a fixed length encoding
-UTF-16 is a variable width encoding.
- A new property dfdl:UTF16Fixed 'yes ¦ no' treat UTF-16 as a fixed width
encoding
15/09: Closed
118
2. Document that an empty sequence that is the content of complex type is
ignored even when it has annotations
One thing to point out is that the authors should avoid
<xs:complexType>
<xs:sequence dfdl:hiddenGroupRef="..."/>
</xs:complexType>
(The same applies to other annotations on sequences, long- or short-form.)
The schema spec will discard that sequence (see [1] definition of
"effective content" clause 2.1.2). The following works:
<xs:complexType>
<xs:sequence>
<xs:sequence dfdl:hiddenGroupRef="..."/>
</xs:sequence>
</xs:complexType>
[1] http://www.w3.org/TR/2004/REC-xmlschema-1-20041028/#key-exg
It is a schema definition error if an empty sequence is the content of a
complex type
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
109
Add 'message' attribute to dfdl:discriminator
01/09: Closed: Conclusion was that this is genuinely useful, and has low
implementation cost. Will add a 'message' attribute to dfdl:discriminator.
43
not started
110
Clarify expression limitations for defineVariable, newVariableInstance and
setVariable
01/09: Closed: Spec should distinguish newVariableInstance defaultValue
from setVariable value.
For newVariableInstance defaultValue, disallow downward references and
references to self (must be usable from the point of declaration)
For setVariable allow downward references and references to self, and
always evaluate at end of component.
(defineVariable defaultValue should be same as newVariableInstance)
43
not started
113
Be specific about regular expression syntax
43
not started
108
Updates to hidden mechanism
43
not started
99
Updates to reflect subsetting and unparser optionality
43
not started
112
Define what conformance to spec means
43
not started
115
Clarify allowed lengths for signed binary integers
43
not started
116
2. xs:minLength
The spec currently states
When an element declaration specifies a default value, and has type
xs:string, then xs:minLength must be specified and must be 1 or greater.
It is a schema definition error otherwise.
The process for defaults and nils means this restriction is no longer
needed.
Agreed
117
3. Is UTF-16 a fixed width or variable width encoding
Proposal
-UCS2 is a fixed length encoding
-UTF-16 is a variable width encoding.
- A new property dfdl:UTF16Fixed 'yes ¦ no' treat UTF-16 as a fixed width
encoding
15/09: Closed
118
2. Document that an empty sequence that is the content of complex type is
ignored even when it has annotations
It is a schema definition error if an empty sequence is the content of a
complex type
Regards
Alan Powell
Development - MQSeries, Message Broker, ESB
IBM Software Group, Application and Integration Middleware Software
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