On Tue, May 7, 2019 at 3:48 AM Steve Hanson <smh@uk.ibm.com> wrote:

Hi Mike

I think what you have highlighted is that there are formats which require that empty elements should not be treated as empty but as missing, which is effectively what IBM DFDL is doing (our code was written prior to action 140 when there was no distinction between empty & missing). That could be achieved with assertions. So maybe we should view the new property as a convenience property for such formats, as well as handling IBM DFDL's behaviour?

If so, then can I suggest new names for the enums, which I think makes the intent clearer?

dfdl:emptyElementPolicy = ( "treatAsMissing" | "treatAsEmpty" )

This only applies when parsing, maybe names should reflect that also?

Further, "treatAsMissing" would imply that a default value was never used when parsing, as they are only used when the representation is empty. I think we can do away with the SDE clause for "treatAsMissing". The clause is only needed for "treatAsEmpty".

IBM DFDL does implement nillable processing, including use of ES as nil literal value.

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: Mike Beckerle <mbeckerle.dfdl@gmail.com>
To: Steve Hanson <smh@uk.ibm.com>
Cc: DFDL-WG <dfdl-wg@ogf.org>
Date: 03/05/2019 21:23
Subject: Re: [DFDL-WG] Action 306 - IBM DFDL behaviour when parsing empty strings

Under testing with the EDIFACT schema (from DFDLSchemas on github) against new code in daffodil, I see that my proposal was not sufficient.
Steve Hanson stated that IBM DFDL current behavior for required empty strings includes "An empty occurrence with no default gives a Processing Error."

I misinterpreted this. I was thinking required occurrence of an array element (as in with index <= minOccurs). But this should not be interpreted that narrowly, but any required occurrence at all including scalar elements. The EDIFACT schema depends on this behavior and backtracking driven by it, in order to work.

So my suggestion for new properties to control this is revised to:

dfdl:emptyElementPolicy enum with values

noEmptyElements - matches current IBM DFDL behavior where
* required elements without default values that are empty (specifically which satisfy the empty syntax - defined below) always cause Processing Errors.
** If a default value is specified that is provided as the value instead. When a default value is specified, then implementations that don't support default values when parsing must issue a runtime SDE here, not a processing error.
* optional elements which satisfy the empty syntax are not added to the infoset. Defaulting is never considered.

emptyElements - matches current description in the DFDL spec where
* required elements: if the string/hexBinary satisfies the empty syntax then required elements are created with an empty string or empty hexBinary as their value. If a default value is specified that is substituted as the value instead. When a default value is specified, then implementations that don't support default values when parsing must issue a SDE here, not a processing error.
* optional elements: if the string/hexBinary satisfies the empty syntax, and emptyValueDelimiterPolicy is not 'none' then an empty string (or hexbinary) is added to the infoset. If emptyValueDelimiterPolicy is 'none', nothing is added to the infoset.

The term "satisfy the empty syntax" means what is found in the data stream may require initiator and/or terminator depending on emptyValueDelimiterPolicy, but if that is 'none' then this is satisfied just by empty string (or no bytes for hexBinary).

Having said the above, I believe we also have to consider nillable elements.

There are two topics:

1) defaulting to nilled - For the case of a nillable element, where the data syntax does NOT match the nil representation, then in the above anywhere a default value is specified, and there is behavior associated with that, well if the element is nillable, and dfdl:useNilAsDefault='true' is specified, then the element is default valued to being nilled. When nillable and dfdl:useNilAsDefault='true' is specified, then implementations that don't support defaulting to nilled when parsing must issue an SDE here, not a processing error.

That takes care of the defaulting aspect of nillables.

The second topic is:

2) nillable, and dfdl:nilValue contains %ES; as one of the possible nil representations. Hence, there is the possibility of empty string (or empty hexBinary) matching the nil representation.

I think the DFDL spec is clear here that if the data stream satisfies the nil syntax, then required or optional, you get a nilled element, period.

Does IBM DFDL implement that behavior? If so great. If not I think we may have to amend the above description of noEmptyElements case for dfdl:emptyElementPolicy to specify the special cases.

...mikeb

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

On Sun, Apr 28, 2019 at 9:36 AM Mike Beckerle <mbeckerle.dfdl@gmail.com> wrote:
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

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
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: 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
Co-Chair, OGF DFDL Working Group
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

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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