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 choice. It matches enough to look like direct dispatch can make a selection, but a further discrimination check has proved that the data doesn't match.

Andy Edwards

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----- Original message -----
From: Mike Beckerle <mbeckerle.dfdl@gmail.com>
Sent by: "dfdl-wg" <dfdl-wg-bounces@ogf.org>
To: "dfdl-wg@ogf.org" <dfdl-wg@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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