[DFDL-WG] clarification needed - choice with both dispatch and discriminator

[Steve Hanson]

The choiceBranchKey resolves the choice PoC and the subsequent 
discriminator resolves any outer PoC. Andy I have modified your words - do 
you agree?

Regards
 
Steve Hanson
IBM Hybrid Integration, Hursley, UK
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
smh at uk.ibm.com
tel:+44-1962-815848
mob:+44-7717-378890



From:   Andrew Edwards/UK/IBM at IBMGB
To:     mbeckerle.dfdl at gmail.com
Cc:     dfdl-wg at ogf.org
Date:   27/01/2017 03:57
Subject:        Re: [DFDL-WG] clarification needed - choice with both 
dispatch        and     discriminator
Sent by:        "dfdl-wg" <dfdl-wg-bounces at ogf.org>



 
Section 15.1.2 also says the following:

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.
 
I have always taken that to mean that a match with direct dispatch is 
taken as definitive, and if a following discriminator check on that choice 
branch fails, then it is a valid error situation.  That is to say, the 
model is accurately saying that the data doesn't match the entire choice. 
It matches enough to look like direct dispatch can make a selection and 
resolve the choice to that branch, but a further discrimination check has 
proved that the entire choice doesn't match the data.
 
 
Andy Edwards
Software Engineer
E-mail: andy.edwards at uk.ibm.com
Snail-mail: MP211, Hursley park, Hursley, WINCHESTER, Hants, SO21 2JN
Phone (internal): 247222
Phone (external): 44-1962-817222
Desk: DE3 F16
The Feynman problem solving Algorithm:
1) Write down the problem
2) Think real hard
3) Write down the answer
            -- Murray Gell-mann in the NY Times
 
 
 
 
----- Original message -----
From: Mike Beckerle <mbeckerle.dfdl at gmail.com>
Sent by: "dfdl-wg" <dfdl-wg-bounces at ogf.org>
To: "dfdl-wg at ogf.org" <dfdl-wg at ogf.org>
Cc:
Subject: [DFDL-WG] clarification needed - choice with both dispatch and 
discriminator
Date: Wed, Jan 25, 2017 11:05 PM
 
 
Section 15.1.2 says you can have both dfdl:choiceBranchKey and a 
discriminator on a choice branch. But it doesn't clarify what the meaning 
of having both is.
 
My assumption is that if you have both, the choice is resolved by the 
choiceDispatchKey/choiceBranchKey, so any discriminator would be about 
some surrounding point of uncertainty outside the choice.
 
I wanted to confirm this is the intention.
 
The alternative semantics would be that the discriminator is redundant, 
and so if it evaluates to true that means nothing at all since the choice 
branch has already been discriminated by the 
choiceDispatchKey/choiceBranchKey. If the discriminator evaluates to 
false, or errors when it evaluates, that would be a parse error that would 
cause the entire choice to fail.
 
Comments?
 
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 
 
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