[DFDL-WG] clarification needed: choice with direct dispatch is/is-not a PoU

[Mike Beckerle]

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
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On Tue, Jul 14, 2020 at 4:08 AM Steve Hanson <smh at 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*
> <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:        Mike Beckerle <mbeckerle.dfdl at gmail.com>
> To:        DFDL-WG <dfdl-wg at 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 at 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* <http://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>
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