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

[Steve Hanson]

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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