[DFDL-WG] questions on setVariable

[Steve Hanson]

1) I'll let Tim comment more on this but a relative expression uses as its 
context the current element on the stack. So using '.' on a simple element 
or its type resolves to the simple element, and using '.' on a complex 
element or a group child (recursively) of a complex element resolves to 
the complex element. Same deal when using the '..' parent axis, so beware 
- as this example shows:

<xs:element name="root">
        <xs:complexType>
                <xs:sequence>
                        <xs:element name="delim" type="xs:string"/>
                        <xs:element name="body">
                                <xs:complexType>
                                        <xs:sequence 
dfdl:separator="{../delim}">

...and not {../../delim} !  This is all implied by the way XPath works. 
XPath only knows about elements. 

2) I don't see why Jonathan's example could give an SDE.  The 
defineVariables will always be executed first. However the result is 
ambiguous, depending on the order each setVariable is executed, as 'bar' 
could end up as 'biff' or 'fooey'. "Schema authors can insert sequences to 
provide more precise control over when variables are set" - quote from 
section 9.5.3 (errata 3.25).

3) To Mike's comment, the order of execution of setVariable and 
newVariableInstance on the same annotation is strictly defined, see 
section 9.5 (errata 3.25)
 
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:     "Cranford, Jonathan W." <jcranford at mitre.org>, 
Cc:     "dfdl-wg at ogf.org" <dfdl-wg at ogf.org>
Date:   10/09/2013 18:23
Subject:        Re: [DFDL-WG] questions on setVariable
Sent by:        dfdl-wg-bounces at ogf.org



Those are both public-comment-class issues. 

The issue of what does "." mean in various places is interesting. It is 
referring to an infoset node, but how to explain exactly which one it 
is....

The out-of-order issue with evaluation that you mention is definitely an 
issue. The schema you gave will work or SDE depending on the order of 
evaluation of the statements and the language is not precise enough to say 
what the order is. I think the order of the setVariable and 
newVariableInstance statements at any annotation point, must be linear 
first to last. The order of setVariable and newVariableInstance combined 
into the resolved set of annotations, but from multiple annotation points 
(e.g., an element and a global type definition it references), those can 
be interleaved in any order.  


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 10, 2013 at 12:53 PM, Cranford, Jonathan W. <
jcranford at mitre.org> wrote:
These questions may go towards public comment if the answers aren't 
straight-forward.  Section references are against latest editor's draft.
 
·        Section 7.9 - 5th paragraph after first example - "A 
dfdl:setVariable value expression may refer to the value of this element 
using a relative path value '.'. "
 
Which element?  
 
If dfdl:setVariable is attached to a simpleType, then the "element" 
referred to here is the element of that type, correct?
 
But when it's attached to group reference, sequence, or choice, is it the 
parent element which contains the group reference, sequence, or choice?
 
 
·        Section 7.9 - next-to-last paragraph:  "However, the order of 
execution among them is not specified."
 
Wouldn't this be ambiguous, then?
 
<xs:schema>
    <xs:annotation>
    <xs:appinfo source="http://www.ogf.org/dfdl/">
      <xs:defineVariable name="bar" />
      <xs:defineVariable name="baz" defaultValue="biff"/>
    </xs:appinfo>
    </xs:annotation>
...
    <xs:element name="foo">
      <xs:annotation>
        <xs:appinfo source="http://www.ogf.org/dfdl/">
          <xs:setVariable ref="bar" value="{$tns:baz}"/>
          <xs:setVariable ref="baz" value="fooey"/>
        </xs:appinfo>
      </xs:annotation>
    </xs:element>
...
</xs:schema>
 
If the order of execution isn't specified, isn't it ambiguous whether 
tns:bar gets the value of "biff" (defaultValue of tns:baz) or "fooey"?
 
 
Respectfully,
 
--
Jonathan W. Cranford 
Senior Information Systems Engineer
The MITRE Corporation (http://www.mitre.org)
 

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