[DFDL-WG] DFDL pointer & offset proposal
Mike Beckerle
mbeckerle.dfdl at gmail.com
Fri Jul 24 08:57:31 EDT 2020
Actually, the target of the indirection is just like an element or
model-group, except without alignment regions. Ugly to have to repeat the
whole grammar for that.
Perhaps we can get away with just documenting that the alignment regions
must be zero length when target of an indirection? I did not try to put
this modified grammar into my commented copy of the proposal (attached).
The "connection" to the indirect pointer or offset is not something that
the grammar can express.
Attached
* my review (with new comments that start with "V4:"),
* my first cut of a DFDL schema for TIFF v6.0,
* a copy of the TIFF v6.0 spec.
I wasn't actually able to pull off TIFF. Comments in the schema discuss
why, which is due to TIFF being a linked list, and I'm not able to
terminate the chain.
There's maybe a trick using negative offsets, but I don't want to consider
that yet, as those are entirely problematic.
Mike Beckerle | OGF DFDL Workgroup Co-Chair | Owl Cyber Defense |
www.owlcyberdefense.com
Please note: Contributions to the DFDL Workgroup's email discussions are
subject to the OGF Intellectual Property Policy
<http://www.ogf.org/About/abt_policies.php>
On Fri, Jul 24, 2020 at 7:03 AM Steve Hanson <smh at uk.ibm.com> wrote:
> Bradd, Mike - as discussed on WG call please review my version of the
> grammar for next call.
>
> The key issue is how to link the *target* of the indirection into the
> main grammar, as it is dis-contiguous.
>
> Regards
>
> Steve Hanson
>
> IBM Hybrid Integration, Hursley, UK
> Architect, *IBM DFDL*
> <http://www.ibm.com/developerworks/library/se-dfdl/index.html>
> Co-Chair, *OGF DFDL Working Group* <http://www.ogf.org/dfdl/>
> *smh at uk.ibm.com* <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: 23/07/2020 14:52
> Subject: Re: [EXTERNAL] Re: [DFDL-WG] DFDL pointer & offset
> proposal
> ------------------------------
>
>
> 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.
>
>
>
> Regards,
>
> *Bradd Kadlecik*
> z/TPF Development
> ------------------------------
> *Phone:* 1-845-433-1573
> * E-mail:* *braddk at us.ibm.com* <braddk at us.ibm.com>
> 2455 South Rd
> 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*
> <http://www.ibm.com/developerworks/library/se-dfdl/index.html>
> Co-Chair, *OGF DFDL Working Group* <http://www.ogf.org/dfdl/>
> *smh at uk.ibm.com* <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
> * E-mail:* *braddk at us.ibm.com* <braddk at us.ibm.com>
> 2455 South Rd
> Poughkeepsie, NY 12601-5400
> United States
>
>
>
>
>
>
> Unless stated otherwise above:
> IBM United Kingdom Limited - Registered in England and Wales with number
> 741598.
> Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU
>
>
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