[DFDL-WG] clarification needed: setVariable - executes before or after framing of the element/model group

[Steve Hanson]

I agree. Btw the language was added by several erratum so is fairly new. 

Perhaps what is missing is some words in the spec that state the resolved 
set of format annotation properties for a simple element describe 
SimpleElement in the data syntax grammar, and so on. 

Regards
 
Steve Hanson
IBM Integration Bus, 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:   Mike Beckerle <mbeckerle.dfdl at gmail.com>
To:     Steve Hanson/UK/IBM at IBMGB
Cc:     "dfdl-wg at ogf.org" <dfdl-wg at ogf.org>
Date:   06/09/2016 20:47
Subject:        Re: [DFDL-WG] clarification needed: setVariable - executes 
before or after framing of the element/model group




Perhaps this is a minor clarification I need. Perhaps this is obvious.

The language you excerpted probably pre-dates the data syntax grammar in 
the spec.

What grammar regions does point (4) " dfdl:sequence or dfdl:choice or 
dfdl:group following property scoping rules" apply to? 

dfdl:group for group references are non-issue since those turn into 
sequence or choice.

I think the answer is perhaps, obvious in retrospect.: it is the Sequence 
or Choice regions, and for simple types it is SimpleElement (not 
SimpleContent) for complex elements it is ComplexElement (not 
ComplexContent). That way it is clear that in every case, framing, 
alignment regions etc., are included. 

So for sequences, what textually appears above/before the dfdl:setVariable 
statement is framing properties of the sequence (in short form, or in long 
form if the dfdl:sequence element is placed above the setVariable 
statemnts). Those can use runtime-valued expressions which refer to the 
variable, and will see the variable after the set has executed. 

This is disconcerting only because of the lexical ordering mis-match with 
the order of execution. 

However, the same is true for asserts and discriminators using 
expressions. Those execute after the setVariables, no matter where they 
appear in lexical order vis a vis the setVariable statement annotations. 

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


On Tue, Sep 6, 2016 at 12:58 PM, Steve Hanson <smh at uk.ibm.com> wrote:
Mike 

>From section 9.5: 
For sequences, choices and group refs: 
1.        dfdl:discriminator or dfdl:assert(s) with testKind 'pattern' 
(parsing only) 
2.        dfdl:newVariableInstance(s) - in lexical order, innermost schema 
component first 
3.        dfdl:setVariable(s) - in lexical order, innermost schema 
component first 
4.        dfdl:sequence or dfdl:choice or dfdl:group following property 
scoping rules 
5.        dfdl:discriminator or dfdl:assert(s) with testKind 'expression' 
(parsing only) 

This says that a setVariable on a group is processed before the format 
annotations of the group, so your example would be allowed.

For discriminators and asserts, when they are executed depends of the 
testKind. If 'pattern' they are executed first. If 'expression' they are 
executed last. 

All seems clear to me - am I missing some subtlety somewhere? 

Regards
 
Steve Hanson
IBM Integration Bus, 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:        Mike Beckerle <mbeckerle.dfdl at gmail.com> 
To:        "dfdl-wg at ogf.org" <dfdl-wg at ogf.org> 
Date:        02/09/2016 16:56 
Subject:        [DFDL-WG] clarification needed: setVariable - executes 
before or after framing of the element/model group 
Sent by:        "dfdl-wg" <dfdl-wg-bounces at ogf.org> 




The spec defines where setVariable executes as a statement relative to 
element processing and model-group processing.

Question is: what does element and model group processing mean: the value 
region of the element, the content region of the element,  or the whole 
element including all framing?

So, for an element, spec says that setVariables run after the element.

Rhetorical question: Does "after" mean after the terminator (including any 
expression for the terminator) has completed?

Yes, because otherwise a element could contain the value of its own 
terminator, and that wouldn't work for lengthKind='delimited' as you would 
need the value to get the terminator to parse the value. 

So 'after' has to mean after the terminator, meaning all framing, and any 
other expression that can affect the length or interpretation in forming 
the element. 

For a model group, the spec says that setVariables run before the model 
group.

So, can a sequence carry a set-variable that sets a variable value that is 
then used in the initiator property of that very sequence?

E.g.,

<xs:sequence dfdl:initiator="{ $init }"> 
   <xs:annotation><xs:appinfo ...> 
       <dfdl:setVariable ref="init">{ ../someplace/else 
}</dfdl:setVariable> 
  </xs:appinfo></xs:annotation> 
   ..... reset of sequence 
</xs:sequence>

If this is not allowed for the initiator, what about for the terminator or 
separator, or outputNewLine or encoding or any other property that 
affects the syntax of the model group? 

What about discriminators/asserts. Do those run before the sequence's 
initiator is matched, or after? E.g., can a discriminator indicate "true", 
but then the initiator fails to match?

When unparsing, you don't execute discriminator/assert at all, so no 
guidance there. 

Maybe this is clear already, but I am not sure if setVariables should run 
before any framing of a model group, or after the framing, but before the 
content region, or before the value region.

...mikeb 

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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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
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