
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@us.ibm.com Poughkeepsie, NY 12601-5400 United States From: Steve Hanson/UK/IBM To: Bradd Kadlecik/Poughkeepsie/IBM@IBMUS Cc: DFDL-WG <dfdl-wg@ogf.org>, "dfdl-wg" <dfdl-wg-bounces@ogf.org>, Mike Beckerle <mbeckerle.dfdl@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@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: [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@us.ibm.com Poughkeepsie, NY 12601-5400 United States