Hi Mike

I believe the rule is that an assert/discriminator expression is evaluated "as soon as it can be". In IBM DFDL, we try to evaluate an expression when it is encountered, and if it can't be evaluated at that time because it references element(s) that do not appear in the infoset, the parser continues but the expression manager registers an interest in the element(s). The expression manager gets notified when the element(s) appear in the infoset and the expression is re-evaluated at that time. If the parser gets to the end of the scope for the assert/discriminator and it is still not evaluated, it is an error. (Tim please correct any mis-information).

Regards

Steve Hanson
Architect, Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh@uk.ibm.com
tel:+44-1962-815848

From: Mike Beckerle <mbeckerle.dfdl@gmail.com>
To: dfdl-wg@ogf.org
Date: 13/09/2012 16:32
Subject: [DFDL-WG] assert and discriminator - no more before/after
Sent by: dfdl-wg-bounces@ogf.org

I am looking in the spec for guidance about the evaluation order of assert statements.

We used to have before/after control properties, but eliminated them.

If I annotate a simpleType'd element with an assert that says { . eq 'x' }, that of necessity references the current value, so must execute after the value has been computed.

If on the other hand I annotate a complexType element with a discriminator that says { ../flag eq 'C1' } then this of necessity must execute before I go after the contents because the whole point is to evalutate the discriminator first.

Did we ever articulate exactly what the rules are here about order of evaluation?

Thanks for reminders

..mikeb

--
Mike Beckerle | OGF DFDL WG Co-Chair
Tel: 781-330-0412
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