[DFDL-WG] questions on setVariable
Suman Kalia
kalia at ca.ibm.com
Tue Sep 10 14:23:45 EDT 2013
Mike - In the use case hilited by Jonathan where 2 annotations are
defined on the same point. I would suggest the execution order to be
based on the lexical order i.e. the order in which annotations appear..
Suman Kalia
IBM Canada Lab
WMB Toolkit Architect and Development Lead
Tel: 905-413-3923 T/L 313-3923
Email: kalia at ca.ibm.com
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From: Mike Beckerle <mbeckerle.dfdl at gmail.com>
To: Steve Hanson <smh at uk.ibm.com>,
Cc: "dfdl-wg at ogf.org" <dfdl-wg at ogf.org>, "dfdl-wg-bounces at ogf.org"
<dfdl-wg-bounces at ogf.org>
Date: 09/10/2013 02:14 PM
Subject: Re: [DFDL-WG] questions on setVariable
Sent by: dfdl-wg-bounces at ogf.org
If the first setVariable executes first, that will read variable baz,
which will cause the second setVariable to SDE because you cannot set
after the variable has been read. I believe this is the right semantics
for this schema, because both these setVariable annotations are written at
the same annotation point.
If the second setVariable executes first, that will assign variable baz,
which is OK, then when the first setVariable executes, it will get the
value that was just assigned.
While the spec says you shouldn't depend on this kind of ordering stuff, I
think it is pretty unsatisfactory if the order is unspecified. Section 9.5
lays out the order of the different kinds of statement annotations
relative to each other, but doesn't say what happens between two
setVariable statements that appear at the same annotation point. I think
the execution order needs to be specific within the annotations at one
annotation point.
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 1:50 PM, Steve Hanson <smh at uk.ibm.com> wrote:
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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