[DFDL-WG] Fwd: [dfdl] initiatedContent w/o initiators

Fri May 31 11:26:15 EDT 2013

Let's table for discussion on Tuesday's WG call.

We also need to walk through the unparser to make sure all the use cases 
are covered.  We've tended to think about dfdl:hiddenGroupRef being used 
with dfdl:outputValueCalc, but that's not always going to be the case, and 
there's choices to consider too.  I think we should follow the standard 
defaulting rules for simple and complex elements when unparsing, but we 
don't say so in the spec. 

Regards

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

From:   Mike Beckerle <mbeckerle.dfdl at gmail.com>
To:     Steve Hanson/UK/IBM at IBMGB, 
Cc:     dfdl-wg at ogf.org
Date:   31/05/2013 14:59
Subject:        Re: [DFDL-WG] Fwd: [dfdl] initiatedContent w/o initiators

I really prefer (b) below. 

My rationale: replace the hidden group by a real group reference to the 
same group. Behavior should not change except for some things show up in 
the infoset that would have been omitted.

That principle should hold anywhere it can, hopefully everywhere.

...mike

On Fri, May 31, 2013 at 4:09 AM, Steve Hanson <smh at uk.ibm.com> wrote:
I agree with Mike's use of a nested choice, I have used this same pattern 
to model a catch-all branch on several occasions. 

I would also add that working out which branch of a choice to take can be 
an expensive operation for a DFDL parser, and one where optimisations will 
be applied. The more alike that the branches are, the more likely it will 
be that the parser can optimise the selection. 

We still need to answer James' question about schema definition error 
though.  The spec says "When the dfdl:hiddenGroupRef property is 
specified, all other DFDL properties are ignored."  which is saying other 
properties are not applicable. In other words, such a sequence is present 
in the schema purely as a device to hide the contents of the group that it 
refers to.  So I think we have a couple of choices when the context in 
which the sequence appears means that it can not be silent about certain 
properties: 

a) The use of dfdl:hiddenGroupRef in that context is a schema definition 
error. 

b) Go to the model group content of the hidden group and see whether its 
properties satisfy the context. 

Regards

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

From:        Mike Beckerle <mbeckerle.dfdl at gmail.com> 
To:        dfdl-wg at ogf.org, 
Date:        31/05/2013 06:37 
Subject:        [DFDL-WG] Fwd:  [dfdl] initiatedContent w/o initiators 
Sent by:        dfdl-wg-bounces at ogf.org 

Forgot to copy the workgroup.

---------- Forwarded message ----------
From: Mike Beckerle <mbeckerle.dfdl at gmail.com>
Date: Fri, May 31, 2013 at 1:32 AM
Subject: Re: [DFDL-WG] [dfdl] initiatedContent w/o initiators
To: "Garriss Jr., James P." <jgarriss at mitre.org>

You need two nested choices. Only the inner one uses initiated content.

<xsd:choice>
    <xsd:choice dfdl:initiatedContent="yes">
           <xsd:element ref="Date"/> 
           <xsd:element ref="From"/> 
           <xsd:element ref="MessageId"/> 
            <xsd:element ref="Subject"/> 
    </xsd:choice> 
    <!-- all unknown and unwanted headers --> 
    <xsd:sequence dfdl:hiddenGroupRef="UnwantedHeadersGroup"/> 
</xsd:choice> 

On Thu, May 30, 2013 at 2:49 PM, Garriss Jr., James P. <jgarriss at mitre.org
> wrote: 
Spec says: 

It is a schema definition error if any children have their dfdl:initiator 
property set to the empty string. 

Does that include a sequence with a hiddenGroupRef? 

For example, part of a schema for email headers is this: 

<xsd:choice dfdl:initiatedContent="yes"> 

<xsd:element ref="Date"/> 

<xsd:element ref="From"/> 

<xsd:element ref="MessageId"/> 

<xsd:element ref="Subject"/> 

<!-- all unknown and unwanted headers --> 

<xsd:sequence dfdl:hiddenGroupRef="UnwantedHeadersGroup"/> 

</xsd:choice> 

Date, From, and the other headers are all elements with initiators, but 
UnwantedHeadersGroup does not have an initiator (because I don’t know it a 
priori).  

Should this throw an error in a DFDL implementation?  I suspect it should, 
though I hope it shouldn’t. 

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-- 
Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | 
www.tresys.com

-- 
Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | 
www.tresys.com
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-- 
Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | 
www.tresys.com

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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