Re: [DFDL-WG] question relevant to evaluation timing - short form

30 Oct 2012

      This makes no sense to me. It doesn't work - you can't spread properties 
across multiple annotations and expect the timing to be different at 
runtime - what if dfdl:length was on one and dfdl:lengthKind on the other?

IBM DFDL disallows this in its xsd for DFDL annotations. Spec should make 
this clear if it doesn't already. 

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:   30/10/2012 17:50
Subject:        [DFDL-WG] question relevant to evaluation timing - short 
form
Sent by:        dfdl-wg-bounces@ogf.org

Can I do this?

<sequence>
   <annotation><appinfo...>
      <dfdl:setVariable ref="foo" .../>
      <dfdl:sequence initiator="{...expression involving foo...}"/>
      <dfdl:newVariableInstance ref="foo" value="{...some 
expression...}"/>
      <dfdl:sequence terminator="{...expression involving foo...}"/>
    </appinfo></annotation>
</element>

See how I am spreading out the evaluation of the runtime-valued properties 
with the setVariable and newVariable stuff.

This works so long as we evaluate everything in schema definition order.

Now let me throw one more wrench (spanner for the UK folks) in the works. 
I'm going to add a short form annotation:

<sequence dfdl:separator="{... expression...}">
   <annotation><appinfo...>
      <dfdl:setVariable ref="foo" .../>
      <dfdl:sequence initiator="{...expression involving foo...}"/>
      <dfdl:newVariableInstance ref="foo" value="{...some 
expression...}"/>
      <dfdl:sequence terminator="{...expression involving foo...}"/>
    </appinfo></annotation>
</element>

Now, a short form annotation is equivalent to a long form conversion 
thereof, but in this case is it this one???

<sequence>
   <annotation><appinfo...>
     <!-- short form annotation comes FIRST when converted. -->
      <dfdl:sequence separator="{...expression ...}"/> <!-- Expression 
cannot use variable foo. -->

      <dfdl:setVariable ref="foo" .../>
      <dfdl:sequence initiator="{...expression involving foo...}"/>
      <dfdl:newVariableInstance ref="foo" value="{...some 
expression...}"/>
      <dfdl:sequence terminator="{...expression involving foo...}"/>

    </appinfo></annotation>
</element>

Or... is it this one:

<sequence>
   <annotation><appinfo...>
      <dfdl:setVariable ref="foo" .../>
      <dfdl:sequence initiator="{...expression involving foo...}"/>
      <dfdl:newVariableInstance ref="foo" value="{...some 
expression...}"/>
      <dfdl:sequence terminator="{...expression involving foo...}"/>

      <!-- short form annotation comes LAST when converted -->
      <dfdl:sequence separator="{...expression ...}"/> <!-- expression 
could use varible foo. -->
    </appinfo></annotation>
</element>

I would argue I prefer the first one, because makes the lexical order of 
appearance consistent with evaluation order. 

...mikeb

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