One clarification: is the IBM DFDL behavior the same for empty hexBinary elements as it is for text strings? I'm going to suggest we need a policy property e.g., dfdl:emptyElementPolicy which is an enum with at least these options: noOptionalEmptyElements - matches current IBM DFDL behavior optionalEmptyElementsWithSyntax - matches current description in the DFDL spec where initiator and/or terminator found triggers creation of an empty string value. (Daffodil implements this.) This would apply (I think) to both types xs:string ad xs:hexBinary I'm open to suggestions for better naming for the property and the property values, but these are the two settings we need I think. I do believe that the latter optionalEmptyElementsWithSyntax behavior is what the DFDL spec describes, and is most consistent given the available properties such as emptyValueDelimiterPolicy. We can make implementation of optionalEmptyElementsWithSyntax a DFDL optional language feature, thereby avoiding issues of conformance with the DFDL standard. 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> On Fri, Apr 5, 2019 at 12:43 PM Steve Hanson <smh@uk.ibm.com> wrote:
Daffodil to perform identical tests but the belief is that they implement the spec as published (except maybe for one bug with default values for strings).
So there is a mis-match between Daffodil and IBM DFDL. It sounds like a new property is going to be needed which toggles the way that empty strings are handled.
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@uk.ibm.com* <smh@uk.ibm.com> tel:+44-1962-815848 mob:+44-7717-378890 Note: I work Tuesday to Friday
From: Steve Hanson/UK/IBM To: DFDL-WG <dfdl-wg@ogf.org> Cc: "Mike Beckerle" <mbeckerle@tresys.com>, "Michele Zundo" < michele.zundo@esa.int>, Bradd Kadlecik/Poughkeepsie/IBM@IBMUS Date: 03/04/2019 12:04 Subject: Action 306 - IBM DFDL behaviour when parsing empty strings ------------------------------
*306* *Confirm IBM DFDL behaviour when parsing empty strings (Steve)* 7/8: IBM DFDL has not fully implemented the behaviour changes arising from action 140 with respect to empty string elements. Daffodil is about to do so. IBM DFDL users have complained about lack of defaults when parsing but other than that appear happy. Are the rules in the spec for empty strings over complicated? Steve to document the behaviour for IBM DFDL to inform the discussion. ... 1/11: In progress - there are a lot of subtle scenarios 15/11: Not discussed ... 7/2/19: No further progress
Some progress :)
*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' 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. *
*IBM DFDL behaviour:*
Required. IBM DFDL does not implement default values when parsing, so an empty occurrence with a default value gives an SDE (to prevent backtracking). An empty occurrence with no default gives a Processing Error. If you need to add an empty string to the infoset, you can add *default=""*(when default values implemented, of course).
Optional. IBM DFDL adds nothing to the infoset regardless of presence of initiator and/or terminator. No way to get empty string into the infoset.
*9.4.2.3 Complex element *
*Required occurrence: An item is added to the Infoset. *
*Optional occurrence: If dfdl:emptyValueDelimiterPolicy is not 'none' then an item is added to the Infoset, otherwise nothing is added to the Infoset. *
*For both required and optional occurrences, the Infoset item may also have a child item. *
* 1. If the first child element of the complex type is a required simple element, then an empty string (type xs:string), empty hexBinary (type xs:hexBinary), or default value will also be added to the Infoset. *
* 2. If the first child element of the complex type is a required complex element, then an item is added to the Infoset (which may itself have a child via (1))*
*IBM DFDL behaviour:*
Required. IBM DFDL follows the spec (modulo 1 when an error would have been thrown, as per its 9.4.2.2 behaviour).
Optional. IBM DFDL follows the spec (modulo 1 when an error would have been thrown, as per its 9.4.2.2 behaviour).
*So ...*
The spec today is consistent in one way, in that for both complex & string elements a) a required empty occurrence always adds to the infoset; & b) an optional empty occurrence adds to the infoset if initiator/terminator present; & c) an optional empty occurrence does not add to the infoset if no initiator/terminator present.
If the simple string behaviour was to change to match IBM DFDL then that consistency is lost, *but* the string behaviour then matches that for other simple types. Section 9.4.2.2 disappears as the behaviour is same as 9.4.2.1. Section 9.4.2.3 becomes as below. We lose the ability to get an empty string into the infoset for an optional string with initiator/terminator.
*9.4.2.3 Complex element *
*Required occurrence: An item is added to the Infoset. *
*Optional occurrence: If dfdl:emptyValueDelimiterPolicy is not 'none' then an item is added to the Infoset, otherwise nothing is added to the Infoset. *
*For both required and optional occurrences, the Infoset item may also have a child item. *
* 1. If the first child element of the complex type is a required simple element, then a default value will also be added to the Infoset. *
* 2. If the first child element of the complex type is a required complex element, then an item is added to the Infoset (which may itself have a child via (1))*
We also need to be sure that any other implementations have not yet implemented the current spec behaviour. Need to check with *DFDL4S *and *IBM TPF.*
To be discussed on next WG call ...
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@uk.ibm.com* <smh@uk.ibm.com> tel:+44-1962-815848 mob:+44-7717-378890 Note: I work Tuesday to Friday 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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