So my albeit clumsy workaround does achieve that. When unparsing the myIVC element doesn't need to be in the infoset. 

Daffodil, when unparsing, would look at the stream of infoset events, NOT find one for myIVC, (it would find one for something else presumably) and assume the choice has to go to the other branch which is an empty sequence.

It would then determine that NOT finding the myOVC element, it would synthesize one, and try to evaluate the OVC to give it a value. Actually, even if it finds myOVC in the infoset it's still going to evaluate the OVC calculation and overwrite the value.

So this may be "a" solution, albeit not necessarily the most desirable one.

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 Wed, Oct 16, 2019 at 4:55 PM Bradd Kadlecik <braddk@us.ibm.com> wrote:

The problem has more to do with "myIVC" not being required. If a default is not permitted then "myIVC" is required during unparse.


Regards,

Bradd Kadlecik
z/TPF Development
Phone: 1-845-433-1573
E-mail: braddk@us.ibm.com
2455 South Rd
Poughkeepsie, NY 12601-5400
United States


Inactive hide details for Mike Beckerle ---10/16/2019 04:50:58 PM---So you are suggesting this: <element name="myOVC" tMike Beckerle ---10/16/2019 04:50:58 PM---So you are suggesting this: <element name="myOVC" type="xs:int" dfdl:outputValueCalc="{

From: Mike Beckerle <mbeckerle.dfdl@gmail.com>
To: Bradd Kadlecik <braddk@us.ibm.com>
Cc: DFDL-WG <dfdl-wg@ogf.org>
Date: 10/16/2019 04:50 PM
Subject: [EXTERNAL] Re: [DFDL-WG] DFDL inputValueCalc restrictions





So you are suggesting this:

        <element name="myOVC" type="xs:int" dfdl:outputValueCalc="{ ../myIVC + 3 }" />
        <element name="myIVC" type="xs:int" dfdl:inputValueCalc="{ compute here }" default="0"/><!-- default only used when unparsing -->

That's not unreasonable.

Question: Can the behavior you need be represented by way of a test for existence of the IVC element?

<element name="myOVC" type="xs:int" dfdl:outputValueCalc="{ if (fn:not(fn:exists(../myIVC))) then 0 else ....do the real computation here.... }"/>
<!-- an optional IVC element -->
<choice>
    <sequence> <!-- IVC can't be root of a choice branch so workaround -->
        <element name="myIVC" dfdl:inputValueCalc="{ compute here }"/>
    </sequence>
    <sequence/> <!-- nothing at all is the other alternative -->
</choice>

That's clumsier, but does achieve, I think, the same behavior without depending on defaulting. It does depend on fn:exists and fn:not functions.


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 Wed, Sep 25, 2019 at 11:49 AM Bradd Kadlecik <braddk@us.ibm.com> wrote:
    Hello,

    I have one item I'd like to discuss at some point regarding inputValueCalc and not allowing the default property to be specified. I have a use case where the default property would be useful for unparse. It makes perfect sense to not allow it for outputValueCalc however.

    The use case is in forming a connection between an inputValueCalc element and an outputValueCalc element where the incoming document might not contain the inputValueCalc element for unparse and a default value would be desired for the outputValueCalc use. This is an item our customers using DFDL would like to make use of but don't want to require the element to always exist for unparse.

Regards,

Bradd Kadlecik
z/TPF Development
Phone: 1-845-433-1573
E-mail: braddk@us.ibm.com
2455 South Rd
Poughkeepsie, NY 12601-5400
United States