No. A discriminator is only ignored if there is no PoU in scope. Otherwise it applies to the nearest in-scope PoU. This is covered in 9.3.3.1 which deals with nested PoUs. It talks about the behaviour of a processing error after a choice has been resolved. Given that an example of a processing error is a discriminator resolving to false, the behaviour of a discriminator evaluating to true is implied.

From the spec for direct dispatch choice ... "When a match is found, it is as if a dfdl:discriminator had evaluated to true on that branch. It is selected as resolution of the choice, and there is no backtracking to try other alternative selections if a processing error occurs."

So in your inner/outer scenario, if you encounter a further discriminator on the resolved branch then that discriminates the OUTER choice.

The IBM schemas for EDI rely on this nested choice behaviour. The inner choice has a branch per possible transaction type, with a discriminator to resolve each one. If a subsequent processing error occurs, it causes the first branch of the OUTER choice to fail, which instead drives the 'Bad Transaction' branch. It would make no difference to the behaviour if the inner choice was resolved by direct dispatch or initiatedContent.

<xsd:complexType name="Transaction">
<xsd:sequence>
<xsd:choice>
<xsd:sequence>
<xsd:choice>
<xsd:element ref="v5010:T997">
<xsd:annotation>
<xsd:appinfo source="http://www.ogf.org/dfdl/">
<dfdl:discriminator>
{fn:contains(./ST/ST01_TransactionSetIdentifierCode,'997')}
</dfdl:discriminator>
</xsd:appinfo>
</xsd:annotation>
</xsd:element>
<xsd:element ref="v5010:T998">
<xsd:annotation>
<xsd:appinfo source="http://www.ogf.org/dfdl/">
<dfdl:discriminator>
{fn:contains(./ST/ST01_TransactionSetIdentifierCode,'998')}
</dfdl:discriminator>
</xsd:appinfo>
</xsd:annotation>
</xsd:element>
<xsd:sequence>
<xsd:annotation>
<xsd:appinfo source="http://www.ogf.org/dfdl/">
<dfdl:assert message="Unsupported message" test="{fn:false()}"/>
</xsd:appinfo>
</xsd:annotation>
</xsd:sequence>
</xsd:choice>
</xsd:sequence>
<xsd:sequence>
<xsd:element ref="v5010:BadTransaction">
</xsd:element>
</xsd:sequence>
</xsd:choice>
</xsd:sequence>
</xsd:complexType>

Bottom line is that you need to be careful with your discriminator placement. Keep each discriminator as close as possible to the PoU it is resolving. You can always look down into structures.

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: 14/07/2020 20:46
Subject: [EXTERNAL] Re: [DFDL-WG] clarification needed: choice with direct dispatch is/is-not a PoU

Ok, then to clarify, if I put a discriminator inside a branch of a choice with direct dispatch, that discriminator should simply confirm the direct dispatch selection of the choice dispatch key? I.e., it is ignored?

So if I have two nested choices, the outer backtracks, the inner is choice by dispatch, then to discriminate the OUTER choice, I have to issue two discriminators in a row. The first is a noop because it applies to the inner choice. The second affects the outer choice?

This would seem to be the implications of having the choice with direct dispatch be a PoU still.

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

On Tue, Jul 14, 2020 at 4:08 AM Steve Hanson <smh@uk.ibm.com> wrote:
I don't agree, because unlike an array with a fixed number of occurrences, it is a processing error if the value of the expression does not match any of the dfdl:choiceBranchKey property values for any of the branches. Which currently causes backtracking because there is a PoU.

I consider direct dispatch as more like the use of dfdl:initiatedContent when resolving a choice.

This is not a behaviour that can be changed in DFDL 1.0, it would affect too many existing schemas. For example, IBM's DFDL schemas for SWIFT make heavy use of direct dispatch.

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: DFDL-WG <dfdl-wg@ogf.org>
Date: 13/07/2020 14:50
Subject: [EXTERNAL] [DFDL-WG] clarification needed: choice with direct dispatch is/is-not a PoU
Sent by: "dfdl-wg" <dfdl-wg-bounces@ogf.org>

Just like an array with a computed number of occurrences, I believe a choice with direct dispatch should have no PoU.

But the spec has this phrase "An xs:choice is always a point of uncertainty. It is resolved sequentially, or by direct dispatch."

Which suggests there is a role for asserts/discriminators in resolving a choice by direct dispatch even though there shouldn't be.

I think we should clarify this to "An xs:choice either is a point of uncertainty, or uses direct dispatch."

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 -- dfdl-wg mailing list dfdl-wg@ogf.org https://www.ogf.org/mailman/listinfo/dfdl-wg

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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