[DFDL-WG] DFDL pointer & offset proposal
Bradd Kadlecik
braddk at us.ibm.com
Thu Jul 23 09:52:28 EDT 2020
I incorporated some of your grammar changes but had a few modifications of
my own we can discuss further in case I'm not understanding some of the
subtleties. I think there may be a case for a nil value with indirection
however as well. I've updated the document to include the changes as
version 4.
(See attached file: DFDL_Indirection_v4.docx)
Regards,
Bradd Kadlecik
z/TPF Development
Phone: 1-845-433-1573 2455 South Rd
E-mail: braddk at us.ibm.com Poughkeepsie, NY
12601-5400
United States
From: Steve Hanson/UK/IBM
To: Bradd Kadlecik/Poughkeepsie/IBM at IBMUS
Cc: DFDL-WG <dfdl-wg at ogf.org>, "dfdl-wg" <dfdl-wg-bounces at ogf.org>,
Mike Beckerle <mbeckerle.dfdl at gmail.com>
Date: 07/10/2020 08:11 AM
Subject: Re: [EXTERNAL] Re: [DFDL-WG] DFDL pointer & offset proposal
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 at 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 at ogf.org>, "dfdl-wg" <dfdl-wg-bounces at ogf.org>,
Mike Beckerle <mbeckerle.dfdl at 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:
[attachment "DFDL_Indirection_v3.docx" deleted by Bradd
Kadlecik/Poughkeepsie/IBM]
Regards,
Bradd Kadlecik
z/TPF Development
Phone: 1-845-433-1573 2455 South Rd
E-mail: braddk at us.ibm.com Poughkeepsie, NY
12601-5400
United States
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