[DFDL-WG] Agenda for OGF DFDL WG call 21 April 2010- 13:00 UK (8:00 ET)

Tue Apr 20 12:08:38 CDT 2010

1. DFDL Specification status 

2 Nils, defaults and unparsing 
3. Current Actions:

4 Expressions during Unparsing.

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1. DFDL Specification status 

2 Nils, defaults and unparsing 

Steve H, Tim and Alan have had further discussions and concluded and new 
property was not required so propose

- Elements that are zero length and elements that are 'missing' from the 
data stream should be treated the same.
- missingValueInitiatorPolicy should be renamed to 
emptyValueInitiatorPolicy to distinguish from a missing infoset value on 
unparsing
- Any 'initiator' policy needs to also include terminators so the 
enumerations should be extended to  "none", "initiator", "terminator", 
"both". and the properties renamed emptyValueDelimiterPolicy  and 
nilValueDelimiterPolicy .

The tables have been reworked

Nils and Defaults on Parsing

initiator region
content region

Logical Value
matching
content
content matches nilValue
nilValueDelimiterPolicy 
must be
initiator or both
nil

Content does not match nilValue

parse content to get value
matching
empty
empty string is a nil value
nilValueDelimiterPolicy 
must be
initiator or both

nil
 A default is specified
emptyValueDelimiterPolicy
 must be
initiator or both
default value 
(may be nil, empty space or value)
empty
content
content matches nilValue
nilValueDelimiterPolicy 
must be
none
nil
content does not match nilValue
Initiator is not specified

parse content to get value
Initiator is  specified

ERROR 
empty
empty
empty string is a nil value
nilValueDelimiterPolicy 
must be
none

nil
A default is specified
emptyValueDelimiterPolicy
 must be
none
default value 
(may be nil, empty space or value)

Nils and Defaults on Unparsing

Logical Value

initiator region contains
content region contains
Nil
(implies nillable)
nilValueDelimiterPolicy 
none
empty
representation of nil 
nilValueDelimiterPolicy 
initiator or both
initiator string
"" (empty string)
(type is xs:string or xs:hexBinary)
emptyValueDelimiterPolicy
 none
empty
empty 
emptyValueDelimiterPolicy
initiator or both
initiator string 
missing
useNilForDefault
nilValueDelimiterPolicy 
none
empty
representation of nil 
nilValueDelimiterPolicy 
initiator or both
initiator string
default is empty string
(type is xs:string or xs:hexBinary)
emptyValueDelimiterPolicy
 none
empty
empty
emptyValueDelimiterPolicy
initiator or both
initiator string
Other default 

initiator string
 representation of the default value.
a non-nil non-empty-string value

initiator string
representation of the logical value

3. 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.
084
Check behaviour of dfdl:inputValueCalc and outputValueCalc.
14/04: no prorgess
085
ALL: publicize Public comments phase to ensure a good review..
14/04: see minutes
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.
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.
089
Need to be able to define unsigned decimal and integer
31/03: MB to agree proposed solution
14/04: MB to agree proposed solution
090
Semantics of separatorPolicy
14/04: Discussion on detecting when complex types should be defaulted. 
Examples needed.

4 Expressions during Unparsing.

In order to reduce complexity and potential performance problems it is 
proposed to 

-  nilValue and occursStopValue should NOT be able to take an expression.

- Very few properties should be allowed to have forward references.

Here's the list of properties that can take an expression, along with some 
suggested restrictions on forward referencing:

byteOrder
backward reference only
encoding
backward reference only
initiator
backward reference only
terminator
backward reference only
separator
backward reference only
outputNewline
backward reference only
length
simple elements : backward reference only.
complex elements : forward reference allowed
Quote "When unparsing with dfdl:lengthKind="explicit", the calculation of 
dfdl:representationLength() returns the value of the dfdl:length 
property." A simple element's length needs to be known in advance, else it 
cannot be parsed. A complex element's length might get resolved while 
parsing its content, so a forward reference within the scope of the 
complex element is possible.

Having said that, we might want to impose a restriction in IBM's DFDL 
processor v1.0 that only backward references are allowed.
escapeCharacter
backward reference only
escapeEscapeCharacter
backward reference only
textNumberDecimalSeparator
backward reference only
textNumberGroupSeparator
backward reference only
textNumberExponentCharacter
backward reference only
binaryFloatRep
backward reference only
textBooleanTrueRep
backward reference only
textBooleanFalseRep
backward reference only
nilValue
backward reference only
Not clear why this needs to be specified as an expression. ( may already 
be on a list of open issues somewhere )
nilIndicatorPath
backward reference only
occursCount
backward reference only
occursStopValue
Not clear why this needs to be specified as an expression. 
[inputValueCalc]
[Parser only] Backward reference only
outputValueCalc
Forward or backward reference

Regards

Alan Powell

Development - MQSeries, Message Broker, ESB
IBM Software Group, Application and Integration Middleware Software
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e-mail: alan_powell at uk.ibm.com

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