I think 'indirect' in property names  should be 'indirection', so I will assume that in what follows.

I am not happy with 'indirectionEmptyValue' or 'indirectionMissingValue'. Both 'empty' and 'missing' are concepts with well-defined meanings in DFDL. How about 'indirectionInactiveValue' or better 'indirectionUnusedValue'?

My stab at an updated grammar below (changes in blue). There is no concept of an empty indirection value or a nil indirection value, so we don't need those clauses.

I also think we can simplify the EnclosedElement construct (changes in red)

Bradd I know you were struggling with how to link the target of the indirection into the main grammar, as it is dis-contiguous. I think we can achieve that by incorporating the target(s) into the Document as a whole.
 
If we think that the concept of an indirection can only ever happen inside a complex type, then we could move IndirectionRep from SimpleElement/ComplexElement to EnclosedElement.

I don't think it is worth getting more specific with IndirectElement. Specifically, it has no LeadingAlignment or TrailingAlignment, but to reflect that requires duplicating most of the rest of the grammar.

You have not disallowed lengthKind 'prefixed' for the 'indirectionType', so that is included in the grammar.  

Productions

Document =  DocumentElement IndirectElement*

DocumentElement = SimpleElement | ComplexElement

SimpleElement = SimpleLiteralNilElementRep | SimpleEmptyElementRep |
                            SimpleNormalRep | IndirectionRep
SimpleEnclosedElement = SimpleElement | AbsentElementRep

ComplexElement = ComplexLiteralNilElementRep | ComplexNormalRep |
                               ComplexEmptyElementRep | IndirectionRep
ComplexEnclosedElement = ComplexElement | AbsentElementRep

EnclosedElement = SimpleElement | ComplexElement | AbsentElementRep

IndirectElement = SimpleElement | ComplexElement

AbsentElementRep = Absent

IndirectionRep = IndirectionLeftFraming PrefixLength IndirectionContent  
                             IndirectionRightFraming

IndirectionLeftFraming = LeadingAlignment
IndirectionRightFraming = TrailingAlignment

IndirectionContent = LeftPadding [ IndirectionValue | IndirectionUnusedValue ] RightPadOrFill

IndirectionValue = SimpleValue

SimpleEmptyElementRep =  EmptyElementLeftFraming EmptyElementRightFraming
ComplexEmptyElementRep =  EmptyElementLeftFraming EmptyElementRightFraming

EmptyElementLeftFraming = LeadingAlignment EmptyElementInitiator PrefixLength
EmptyElementRightFraming = EmptyElementTerminator TrailingAlignment

SimpleLiteralNilElementRep = NilElementLeftFraming [NilLiteralCharacters |
                                                 NilElementLiteralContent] NilElementRightFraming
ComplexLiteralNilElementRep = NilElementLeftFraming NilLiteralValue NilElementRightFraming

NilElementLeftFraming = LeadingAlignment NilElementInitiator PrefixLength
NilElementRightFraming = NilElementTerminator TrailingAlignment

NilElementLiteralContent = LeftPadding  NilLiteralValue RightPadOrFill

SimpleNormalRep = LeftFraming PrefixLength SimpleContent RightFraming
ComplexNormalRep = LeftFraming PrefixLength ComplexContent ElementUnused
                                    RightFraming

LeftFraming = LeadingAlignment Initiator
RightFraming = Terminator TrailingAlignment

PrefixLength = SimpleContent | PrefixPrefixLength SimpleContent
PrefixPrefixLength = SimpleContent

SimpleContent =   LeftPadding [ NilLogicalValue | SimpleValue ]  RightPadOrFill

ComplexContent = Sequence | Choice

Sequence =  LeftFraming SequenceContent RightFraming
SequenceContent = [ PrefixSeparator  EnclosedContent [ Separator EnclosedContent ]*
                                   PostfixSeparator ]

Choice = LeftFraming ChoiceContent RightFraming
ChoiceContent = [ EnclosedContent ] ChoiceUnused

EnclosedContent = [ EnclosedElement | Array | Sequence | Choice ]

Array = [ EnclosedElement [ Separator EnclosedElement ]*  [ Separator StopValue] ]

StopValue = SimpleElement

LeadingAlignment = LeadingSkip AlignmentFill
TrailingAlignment = TrailingSkip
RightPadOrFill = RightPadding | RightFill | RightPadding RightFill



Regards
 
Steve Hanson

IBM Hybrid Integration, Hursley, UK
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
smh@uk.ibm.com
tel:+44-1962-815848
mob:+44-7717-378890
Note: I work Tuesday to Friday



From:        Bradd Kadlecik/Poughkeepsie/IBM
To:        Steve Hanson/UK/IBM
Cc:        DFDL-WG <dfdl-wg@ogf.org>, "dfdl-wg" <dfdl-wg-bounces@ogf.org>, Mike Beckerle <mbeckerle.dfdl@gmail.com>
Date:        09/07/2020 15:09
Subject:        Re: [EXTERNAL] Re: [DFDL-WG] DFDL pointer & offset proposal



I have updated the document proposal with proposed DFDL grammar changes:



Regards,

Bradd Kadlecik
z/TPF Development

Phone: 1-845-433-1573
E-mail: braddk@us.ibm.com
2455 South Rd
Poughkeepsie, NY 12601-5400
United States




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