September 2019 - dfdl-wg

DFDL pointer & offset proposal
by Bradd Kadlecik 30 Apr '20

30 Apr '20

Here's what I've put together regarding the pointer & offset proposal for the next meeting's review. (See attached file: DFDL_Indirection.docx) Regards, Bradd Kadlecik z/TPF Development Phone: 1-845-433-1573 2455 South Rd E-mail: braddk(a)us.ibm.com Poughkeepsie, NY 12601-5400 United States From: Steve Hanson/UK/IBM To: Bradd Kadlecik/Poughkeepsie/IBM@IBMUS Cc: "Mike Beckerle" <mbeckerle(a)tresys.com>, "Michele Zundo" <michele.zundo(a)esa.int> Date: 04/05/2019 12:42 PM Subject: Re: Latest OGF DFDL WG Call Minutes |------+------------------------------------------------------------------| | No |Action | |------+------------------------------------------------------------------| | 309 |Create example scenarios to illustrate offset & pointer | | |requirements (Bradd) | | |5/4/19: Daffodil have a draft proposal for offset support, TPF | | |have experimental implementation for pointer support. Need | | |examples to show the requirement, especially unparsing. | |------+------------------------------------------------------------------| Regards Steve Hanson IBM Hybrid Integration, Hursley, UK Architect, IBM DFDL Co-Chair, OGF DFDL Working Group smh(a)uk.ibm.com tel:+44-1962-815848 mob:+44-7717-378890 Note: I work Tuesday to Friday From: Steve Hanson/UK/IBM To: Bradd Kadlecik/Poughkeepsie/IBM@IBMUS Cc: "Mike Beckerle" <mbeckerle(a)tresys.com>, "Michele Zundo" <michele.zundo(a)esa.int> Date: 05/04/2019 10:29 Subject: Re: Latest OGF DFDL WG Call Minutes I can see a difference between offsets and pointers. If I follow an offset and parse an element x then I won't automatically jump back to where I was - the next element y I parse will continue from location offset + length x unless I use offset again to jump back to the original location. If I follow a pointer and parse an element x, then the next element y I parse will continue from original location + length(pointer). Regards Steve Hanson IBM Hybrid Integration, Hursley, UK Architect, IBM DFDL Co-Chair, OGF DFDL Working Group smh(a)uk.ibm.com tel:+44-1962-815848 mob:+44-7717-378890 Note: I work Tuesday to Friday From: Steve Hanson/UK/IBM To: Bradd Kadlecik/Poughkeepsie/IBM@IBMUS Cc: "Mike Beckerle" <mbeckerle(a)tresys.com>, "Michele Zundo" <michele.zundo(a)esa.int> Date: 04/04/2019 09:42 Subject: Re: Latest OGF DFDL WG Call Minutes This is a proposal from the Daffodil team for offset support, needed for formats like TIFF and if we ever want to be able to handle zip files. https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=74687382 I think this proposal can implement your requirement - the dfdl:offset property can be an expression that refers to another element (your pointer element), which can be hidden so as not to appear in the infoset. I think what you are proposing is a more convenient way of handling offsets that are defined dynamically in the data, as opposed to defined statically with fixed values (though as I said below I need unparsing explained). But I may be mis-understanding your use cases. Regards Steve Hanson IBM Hybrid Integration, Hursley, UK Architect, IBM DFDL Co-Chair, OGF DFDL Working Group smh(a)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@IBMGB Cc: "Mike Beckerle" <mbeckerle(a)tresys.com>, "Michele Zundo" <michele.zundo(a)esa.int> Date: 03/04/2019 16:50 Subject: Re: Latest OGF DFDL WG Call Minutes Ok, I'll work on putting a scenario together for various pointer setups (array, complex element, string) and show how it looks for both the JSON and the binary. I'm currently at a conference this week but will be returning late Thursday so expect to be available for the call Friday. I presented the TPF specific pointer implementation at the conference this week and there are some that will be trying to use it soon. Regards, Bradd Kadlecik z/TPF Development Phone: 1-845-433-1573 2455 South Rd E-mail: braddk(a)us.ibm.com Poughkeepsie, NY 12601-5400 United States From: Steve Hanson/UK/IBM To: Bradd Kadlecik/Poughkeepsie/IBM@IBMUS Cc: dfdl-wg(a)ogf.org, "Mike Beckerle" <mbeckerle(a)tresys.com>, "Michele Zundo" <michele.zundo(a)esa.int> Date: 04/03/2019 10:29 AM Subject: Re: Latest OGF DFDL WG Call Minutes Hi Bradd I have a few questions please ... inline below. I'm still going to need a real worked example, starting with some actual data and its schema, what it appears like after paring in the infoset, and how unparsing lays it back out again. Are you able to make the rescheduled call this Friday? Regards Steve Hanson IBM Hybrid Integration, Hursley, UK Architect, IBM DFDL Co-Chair, OGF DFDL Working Group smh(a)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@IBMGB Cc: dfdl-wg(a)ogf.org, "Mike Beckerle" <mbeckerle(a)tresys.com>, "Michele Zundo" <michele.zundo(a)esa.int> Date: 27/02/2019 22:22 Subject: Re: Latest OGF DFDL WG Call Minutes Regarding proposal for offsets and pointers: The following are the properties to be defined: SMH: I was expecting to see these properties only on dfdl:element, especially as you say '...the element contents... ? indirectKind Enum Valid values 'pointer', 'offset' (there is also a thought of objectId or refId for handling BSON but not at this time) Specifies the type of indirection used to access the element contents in the data stream. Annotation: dfdl:element, dfdl:simpleType, dfdl:choice, dfdl:sequence, dfdl:group SMH: I am missing the distinction between offset and pointer. Is one relative to current position and the other relative to start of bitstream? SMH: In earlier DFDL proposals for offset support, we had used the term to refer to a property to be used to establish position of the current element instead of assuming the current element followed straight after the previous one. It would allow sparse modelling of fixed structures. The offset could be relative to start of bitstream or some other point. I don't think that's what you mean when you say 'offset' so I will refer to your new concept as 'pointer'. SMH: Assuming that indirectKind is a normal DFDL property, it can be in scope. It would therefore need to have an enum 'None' which would be the default used in most schemas. indirectLength Non-negative Integer or DFDL expression Specifies the length of the indirection in units according to the indirectUnits property. Annotation: dfdl:element, dfdl:simpleType, dfdl:choice, dfdl:sequence, dfdl:group indirectUnits Enum Valid values 'bytes','bits' Specifies the units to be used for reading or writing the indirection according to indirectLength. The default value is 'bytes'. Annotation: dfdl:element, dfdl:simpleType, dfdl:choice, dfdl:sequence, dfdl:group SMH: I think a better approach is to provide a property dfdl:indirectType, instead of indirectLength/indirectUnits, which refers to a simple type (not element) that carries its own lengthKind, length & lengthUnits properties. Similar idea to dfdl:prefixLengthType. That allows a lot of flexibility on how the pointer can appear. offsetBase non-empty string containing an absolute or relative XPath expression for the base element. Annotation: dfdl:element, dfdl:simpleType, dfdl:choice, dfdl:sequence, dfdl:group The proposal would be to have the contents of the indirection be after the LeadingAlignment and before the TrailingAlignment. This would mean the aligment and skip factors apply to the indirection values in the data stream instead of the the contents of the indirection. SMH: Agree. This also then means in an array element, each element has its own indirection value (pointer or offset) and the alignment,skip factors then apply to each of these indirection values. SMH: Do you mean '...each occurrence...' ? It would be thought that the indirection values apply only to the data stream and not the infoset. During parse when the infoset is populated from the data stream, the indirection values are replaced by the contents. During unparse, the indirection values don't exist in the infoset and are created during the writing to/creation of the data stream. SMH: I agree that the indirection should be a purely physical thing, but I am not clear how the value is filled in when unparsing. Where does the value come from? outputValueCalc? Or maybe it's not needed when unparsing, and the data is always contiguous? For pointers, a null pointer creates the scenario of either nil representation or empty representation depending on whether or not nillable is defined as true. Unless default values (or 0 occurrence) are defined for all underlying content, then this is a processing error. During unparse, the only scenario in which a null pointer would be created is for a nil representation. SMH: This needs more thought. The nil & default properties apply to the contents of the indirection, not to the pointer. If you want to give a nil semantic to the pointer value itself, then that would require a new enum for dfdl:nilKind. I don't see why a pointer value 0 can't be treated like any other indirection value. A missing pointer is an error - it must be present - there is no way to control optionality because minOccurs/maxOccurs apply to the contents. (Alternatively, if you want the concepts of nil, default, occurs to apply to the indirect value, then dfdl:indirectType could point at an element instead of a simple type - but that seems way too over engineered). Examples: The following is the definition for the address of a null-terminated string in which the string address may be NULL as indicated by a nillable value of true: <xs:element name="myString" type="xs:string" dfdl:lengthKind="delimited" dfdl:encoding="UTF-8" dfdl:terminator="%NUL;" dfdl:indirectKind="pointer" dfdl:indirectLength="8" dfdl:indirectUnits="bytes" nillable="true" /> The following is the definition for an array of three 4 byte addresses of a complex element defined by ns0:myStruct: <xs:element name="myArray" type="ns0:myStruct" dfdl:lengthKind="implicit" dfdl:indirectKind="pointer" dfdl:indirectLength="4" dfdl:indirectUnits="bytes" minOccurs="3" maxOccurs="3" dfdl:occursCountKind="fixed" /> The following is the definition for a 4 byte offset to a 100 byte hexBinary value from the start of the parent element definition: <xs:element name="myData" type="xs:hexBinary" dfdl:lengthKind="explicit" dfdl:length="100" dfdl:lengthUnits="bytes" dfdl:indirectKind="offset" dfdl:indirectLength="4" dfdl:indirectUnits="bytes" dfdl:offsetBase=".." /> SMH: I don't see how unparsing works. What provides the value? The proposal would also allow for the following optional item but I don't currently see a need for this: dfdl:offsetKind with values "startToStart" or "endToStart" - indicates if the offset is from the start of the base element or the end of the base element. I tried getting this out before my vacation so it might take a little bit to respond for issues. Thank you for your time. Regards, Bradd Kadlecik z/TPF Development Phone: 1-845-433-1573 2455 South Rd E-mail: braddk(a)us.ibm.com Poughkeepsie, NY 12601-5400 United States From: Steve Hanson/UK/IBM To: dfdl-wg(a)ogf.org Cc: "Mike Beckerle" <mbeckerle(a)tresys.com>, "Michele Zundo" <michele.zundo(a)esa.int>, Bradd Kadlecik/Poughkeepsie/IBM@IBMUS Date: 02/07/2019 12:32 PM Subject: Latest OGF DFDL WG Call Minutes Please find minutes from the latest call at https://redmine.ogf.org/projects/dfdl-wg/news Regards Steve Hanson IBM Hybrid Integration Architect, IBM DFDL, Co-Chair, OGF DFDL Working Group smh(a)uk.ibm.com tel:+44-1962-815848 mob:+44-7717-378890 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 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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clarification needed: unparsing and hidden group choices and choices with dfdl:choiceDispatchKey
by Mike Beckerle 13 Dec '19

13 Dec '19

So interesting issue. Comes up as part of our experience implementing the advanced expression language features: hidden groups, and computed elements. We have hidden groups in DFDL. If a xs:choice is inside a hidden group, then by definition, when unparsing, elements corresponding to some branch of the choice are not in the Infoset. DFDL spec clearly states that dfdl:outputValueCalc is not allowed on the head of a choice branch. But elements inside hidden groups must have dfdl:outputValueCalc, or a default value, otherwise there's no way for them to be filled in as part of the augmented infoset. So the only way a choice can be inside a hidden group is if the head of the choice branches have default values. This is not sufficient. I do not think it was our intention to make hidden groups incapable of holding things complex enough to contain a choice. Rather, the point is to be able to hide things that have excess complexity needed only for parsing/unparsing, so that they need not appear in the final Infoset. So if a choice is allowed inside a hidden group, then a mechanism is needed by which when unparsing a choice branch is selected based on values of other parts of the Infoset, and then the elements of that branch are computed and added to the augmented infoset. Note that without hidden groups, this problem never arises, as the Infoset always has to take a position on choice branches by having an unambiguous element in it. There are 3 cases: 1. unparsing an xs:choice where for parsing, each branch has a discriminator, or is resolved by the simple "first successful parse" rule. 2. unparsing an xs:choice with dfdl:choiceDispatchKey 3. unparsing xs:choice with dfdl:initiatedContent='yes' For all cases, I suggest we must remove the restriction on dfdl:outputValueCalc being disallowed on choice branch head. For (1). First branch where the branch can be constructed successfully is added to the augmented infoset. This is a case where an unparse error is non-fatal, and causes a form of unparser backtracking through alternatives. Branches would be attempted in schema order. For (2) I suggest dfdl:unparseChoiceDispatchKey, evaluated at unparse time only. Produces a choice branch key. That choice branch is then constructed, and default values or dfdl:outputValueCalcs are used to fill in values. (BTW: this is the driving use case we have in Daffodil for this issue.) For (3).... I have no specific solution. I think it may not actually be a separate case and has to be treated as (1) or (2). Comments/Discussion?

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DFDL inputValueCalc restrictions
by Bradd Kadlecik 16 Oct '19

16 Oct '19

Hello, I have one item I'd like to discuss at some point regarding inputValueCalc and not allowing the default property to be specified. I have a use case where the default property would be useful for unparse. It makes perfect sense to not allow it for outputValueCalc however. The use case is in forming a connection between an inputValueCalc element and an outputValueCalc element where the incoming document might not contain the inputValueCalc element for unparse and a default value would be desired for the outputValueCalc use. This is an item our customers using DFDL would like to make use of but don't want to require the element to always exist for unparse. Regards, Bradd Kadlecik z/TPF Development Phone: 1-845-433-1573 2455 South Rd E-mail: braddk(a)us.ibm.com Poughkeepsie, NY 12601-5400 United States

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Problem: simple format that is impossible to model
by Mike Beckerle 03 Oct '19

03 Oct '19

I have a dead-simple little format: data/data/data/data data/data/data/data it is lines of "/" separated strings. All elements are optional. I simply want this: data//data to round trip. For that to happen I need it to parse into <field>data</field><field></field><field>data</field> That is, I require that empty field element in the middle to be created and put into the infoset. I can find no way to do this. The strings have no initiator/terminator, so dfdl:emptyValueDelimiterPolicy is not relevant. All the elements are optional, so default values aren't relevant. The spec states: 9.4.2.2 Simple element (xs:string or xs:hexBinary) Required occurrence: If the element has a default value then an item is added to the infoset using the default value, otherwise an item is added to the Infoset using empty string (type xs:string) or empty hexBinary (type xs:hexBinary) as the value. Optional occurrence: If dfdl:emptyValueDelimiterPolicy is not 'none'[12] <https://daffodil.apache.org/docs/dfdl/#_ftn12> then an item is added to the Infoset using empty string (type xs:string) or empty hexBinary (type xs:hexBinary) as the value, *otherwise nothing is added to the Infoset*. There are errata/actions to clarify wording here around dfdl:emptyValueDelimiterPolicy being in effect or not (because there is no initiator/terminator for it to use as opposed to the property in isolation just being 'none'). But that doesn't change anything about this issue. If this very simple format is not possible, then we need a property or new property enum value that makes it possible. Thoughts? Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | www.tresys.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>

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RFC 2119 word usage in DFDL Spec
by Mike Beckerle 30 Sep '19

30 Sep '19

In studying Tracker 304 https://redmine.ogf.org/issues/304 I have found that there are many uses of words like must and should, which are not specifically in accord with the notions of RFC 2119, because they are not involved in statements about requirements. For example, in section 2.3.1.1 Usually, the behavior of the unparser is symmetric to the behavior of the parser; however, there are cases where the DFDL schema will accept several equivalent representations for the same logical data. In this case it would be ambiguous which of these equivalent representations should be produced by the unparser. The DFDL standard contains representation properties which are used to eliminate this ambiguity. It is a schema definition error if a DFDL schema is being used to unparse data and there is any ambiguity about the representation. We can either ignore such issues, because the context doesn't require us to consider this a requirement statement, or reword so as to avoid RFC2119 terms. I am not sure it is worth changing this prose in all the places where this sort of thing happens. The word 'should' is less problematic than the word 'must' of which there are hundreds of occurrences. Thoughts? Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | www.tresys.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>

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Re: [DFDL-WG] DFDL pointer & offset proposal
by Bradd Kadlecik 25 Sep '19

25 Sep '19

Properties for indirection: The following properties allow for data to be accessed in a non-sequential or non-contiguous format by using indirection values to locate the data contents. When parsing, the indirection value is used to access the contents in the data stream to populate the infoset. When unparsing, an indirection value is created to store the contents in the data stream when creating the data stream from the infoset. The indirection value does not exist in the infoset, but only in the data stream. The LeadingAlignment and TrailingAlignment regions apply to the indirection value in the data stream. The initiator and terminator as well as all regions between the LeftFraming and RightFraming regions are applied to the data content accessed through the indirection value. Property Name | Description ----------------------+-------------------------------------------------------- indirectKind | Enum | | Specifies the type of indirection value used to | access the the contents in the data stream. | | Valid values ‘pointer’, ‘offset’, ‘none’. | | ‘pointer’ means a numeric value gives an | implementation-dependent starting position of the | content. | | ‘offset’ means a numeric value that when added to | indirectBase gives the starting position of the | content. | | ‘none’ means no indirection is used and is the | default value. | | Annotation: dfdl:choice, dfdl:element, dfdl:group, | dfdl:simpleType, dfdl:sequence ----------------------+-------------------------------------------------------- indirectType | QName | | Name of a simple type derived from xs:integer or any | subtype of it. | | This type, with its DFDL annotations specifies the | representation of the indirection value. | | It is a schema definition error if the xs:simpleType | specifies any of: | · dfdl:lengthKind 'delimited', 'endOfParent', or | 'pattern' | · dfdl:lengthKind 'explicit' where length is an | expression | · dfdl:outputValueCalc | · dfdl:initiator or dfdl:terminator other than | empty string | · dfdl:alignment other than '1' | · dfdl:leadingSkip or dfdl:trailingSkip other | than '0'. | | Annotation: dfdl:choice, dfdl:element, dfdl:group, | dfdl:simpleType, dfdl:sequence ----------------------+-------------------------------------------------------- indirectBase | String | | Provides the relative path to a prior element upon | which the offset is based. | | Required only when dfdl:indirectKind is ‘offset’. | | Annotation: dfdl:choice, dfdl:element, dfdl:group, | dfdl:simpleType, dfdl:sequence ----------------------+-------------------------------------------------------- indirectEmptyValue | Integer | | Specifies the indirection value that indicates when | the data content is empty. If this property is | specified, all underlying elements must contain a | default value specification or it is a schema | definition error. | | Annotation: dfdl:choice, dfdl:element, dfdl:group, | dfdl:simpleType, dfdl:sequence The following example illustrates how to describe a pointer to a null-terminated string (common in languages like C). <xs:element name="myString" type="xs:string" dfdl:lengthKind="delimited" dfdl:encoding="UTF-8" dfdl:terminator="%NUL;" dfdl:indirectKind="pointer" dfdl:indirectType="ptr32_t" dfdl:indirectEmptyValue="0" default=""/> <xs:simpleType name="ptr32_t" dfdl:representation="binary" dfdl:lengthKind="explicit" dfdl:length="4" dfdl:byteOrder="bigEndian"> <xs:restriction base="integer"/> </xs:simpleType> The data stream may look like the following for a string value of “test”. Location Hex values 00000000 0012A000 0012A000 7465737400 t e s t The following example defines an array of 3 pointers to complex elements defined by ns0:myStruct. <xs:element name="myArray" type="ns0:myStruct" dfdl:lengthKind="implicit" dfdl:indirectKind="pointer" dfdl:indirectType="ptr32_t" dfdl:indirectEmptyValue="0" minOccurs="3" maxOccurs="3" dfdl:occursCountKind="fixed"/> <xs:simpleType name="ptr32_t" dfdl:representation="binary" dfdl:lengthKind="explicit" dfdl:length="4" dfdl:byteOrder="bigEndian"> <xs:restriction base="integer"/> </xs:simpleType> The data stream may look like the following with the contents of each occurrence in a different location and the contents of the 2nd occurrence being empty. Location Hex values 00000000 00147000 00000000 00146000 00146000 ... 00147000 ... The following example defines an offset to a 6 byte hexBinary value with the offset being calculated from the start of the current element. <xs:element name="myData" type="xs:hexBinary" dfdl:lengthKind="explicit" dfdl:length="6" dfdl:indirectKind="offset" dfdl:indirectType="uint" dfdl:indirectBase="."/> <xs:simpleType name="uint" dfdl:representation="binary" dfdl:lengthKind="explicit" dfdl:length="4" dfdl:byteOrder="bigEndian"> <xs:restriction base="unsignedInt"/> </xs:simpleType> The data stream may look like the following for a hexBinary value of “123456789ABC”. Location Hex values 00000100 00000108 00000208 123456789ABC Regards, Bradd Kadlecik z/TPF Development Phone: 1-845-433-1573 2455 South Rd E-mail: braddk(a)us.ibm.com Poughkeepsie, NY 12601-5400 United States

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OGF DFDL WG Call on 2018-09-26 - cancelled
by Steve Hanson 25 Sep '19

25 Sep '19

Apologies but I have a deadline coming up and not able to do anything DFDL WG related right now. Regards Steve Hanson Architect, IBM DFDL Co-Chair, OGF DFDL Working Group Hursley, UK smh(a)uk.ibm.com tel:+44-1962-815848

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Re: [DFDL-WG] DFDL inputValueCalc restrictions
by Michele Zundo 25 Sep '19

25 Sep '19

I’m also not seeing coming from in dfdl-wg... > On 25 Sep 2019, at 16:25 , Beckerle, Mike <mbeckerle(a)tresys.com> wrote: > > ((( > Strangely, this thread not showing up on dfdl-wg(a)ogf.org. > but is coming to me direct at my tresys email because I am directly addressed also. > > Bradd are you getting bounce-back from the OGF mail system? > > I'll respond here, but I'd prefer that this happen on the ogf dfdl-wg(a)ogf.org email list. > ))) > > > Daffodil project has been building up an experience document about inputValueCalc, outputValueCalc, and hidden groups. The draft is on our wiki here: > > https://s.apache.org/daffodil-experience-with-computed-elements <https://s.apache.org/daffodil-experience-with-computed-elements> > > This will get finalized into an OGF Experience document and a number of changes/corrections to the DFDL spec will come out of it I expect. > > We already have identified that disallowing IVC and OVC on the same element is unnecessary and sometimes you want this. Your case with default values sounds similar. > > We can incorporate your contribution to the experience document. Take a look and see if the existing discussion can just be enhanced with a sentence about also allowing default on an IVC element. If so I can edit and add it there. > From: Bradd Kadlecik <braddk(a)us.ibm.com> > Sent: Wednesday, September 25, 2019 9:48 AM > To: dfdl-wg(a)ogf.org <dfdl-wg(a)ogf.org> > Cc: Steve Hanson <smh(a)uk.ibm.com>; Beckerle, Mike <mbeckerle(a)tresys.com>; Michele Zundo <michele.zundo(a)esa.int>; Liam O'Neill <WILONEIL(a)uk.ibm.com>; DFDL Schemas for Commercial and Scientific Data Formats <smhdfdl(a)gmail.com> > Subject: DFDL inputValueCalc restrictions > > Hello, > > I have one item I'd like to discuss at some point regarding inputValueCalc and not allowing the default property to be specified. I have a use case where the default property would be useful for unparse. It makes perfect sense to not allow it for outputValueCalc however. > > The use case is in forming a connection between an inputValueCalc element and an outputValueCalc element where the incoming document might not contain the inputValueCalc element for unparse and a default value would be desired for the outputValueCalc use. This is an item our customers using DFDL would like to make use of but don't want to require the element to always exist for unparse. > > Regards, > > Bradd Kadlecik > z/TPF Development > Phone: 1-845-433-1573 > E-mail: braddk(a)us.ibm.com <mailto:braddk@us.ibm.com> > 2455 South Rd > Poughkeepsie, NY 12601-5400 > United States > >

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Cancelled: OGF DFDL Working Group call
by Steve Hanson 25 Sep '19

25 Sep '19

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clarifications needed for %ES; and %WSP*; entities
by Mike Beckerle 18 Sep '19

18 Sep '19

Currently, we have gaps in the spec. E.g., in discussion of dfdl:initiator, the spec says %ES; cannot appear alone in the list, but there is nothing prohibiting one from just using dfdl:initiator="%ES;%ES;" or dfdl:initiator="%ES: %ES;" to trivially work around this constraint, even though both of these definitions are nonsense. To avoid repeated discussion of this topic for each of initiator, terminator, and separator, these statements need to be made where ES and WSP* are defined, or in some other central location that discusses DFDL String Literals and whitespace separated lists thereof. %ES; can never appear as part of any other token. I.e., "%ES;A" is the same as just "A" regardless of what "A" is. So %ES; can only appear as a solitary token in a whitespace separated list of delimiter tokens or nilValue tokens. Furthermore, %ES; cannot be repeated in the list, since "%ES; %ES;" means the same thing as just "%ES;". %WSP*; similarly cannot be repeated in the list meaningfully, so that should be prohibited as well. (In fact repeating any token multiple times in the list can be prohibited.) %WSP*; cannot be combined with %WSP+;, as the combination is equivalent to just %WSP+; by itself. Furthermore %WSP*;%WSP*; means the same as %WSP*; alone, so that should also be prohibited. If we add these clarifications, then statements about how %ES; and %WSP*; and their specific constraints for dfdl:initiator and dfdl:terminator and dfdl:separator need not repeat these statements, and the constraints they express do not have obvious gaps. Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | www.tresys.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>

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