[dfdl-wg] Telcon Notes

[Geoff Judd]

Martin,
            Please see my comments below.

Regards,

Geoff Judd
Websphere MQ Integrator Development
IBM UK Ltd
Hursley

Telephone:  +44-1962-818461
E-mail:           JUDDG at uk.ibm.com




"Westhead, Martin \(Martin\)" <westhead at avaya.com> 
13/12/2005 17:57

To
Geoff Judd/UK/IBM at IBMGB
cc
<dfdl-wg at ggf.org>
Subject
RE: [dfdl-wg] Telcon Notes






Hi Geoff,
 
I?ll certainly put this on the agenda. If anyone has anything else please 
let me know.
 
Also some comments:
 
1.      I?d like to understand how variables relate to parameters, 
specifically:
a.      Could we actually define variables to be user-defined parameters? 
(if not, why not?)
b.      If (a) doesn?t work can we have variables use the same scoping 
rules as parameters?

GJ: This is a good point which I have omitted from the semantics document. 
However I had considered this when looking at late binding of schemas and 
runtime schemas. I think variables in DFDL should be similar to XSLT 
parameters. That is the value of a variable can be set externally although 
the mechanism for this will not be specified. If a value of a variable is 
set externally it is the equivalent of binding a value to the variable so 
it cannot have another value bound to it. Also I think that for a valoue 
to be set externally the declaration of the variable should be made at the 
schema level.  
 
2.      In the extensibility group we have been talking about reference 
direction. It was proposed that XPaths in a DFDL document can only refer 
to elements higher up the document (i.e. backwards only) they cannot 
reference things below them (which will not yet have been parsed). With 
the use of ?hidden layers? this can be done without loss of generality. 
 
I would suggest that variable references should work this way. I.e you are 
only allowed to refer to data that has already been parsed.

GJ: I agree that only variables that have been declared and have either a 
default value or a value bound to them can be referenced. If this is not 
the case it will result in a runtime error. Does this answer your question 
or have I mis-understood what you mean ?
 
Thanks,
 
Martin
 
 
 

From: Geoff Judd [mailto:JUDDG at uk.ibm.com] 
Sent: Tuesday, December 13, 2005 9:34 AM
To: Westhead, Martin (Martin)
Cc: dfdl-wg at ggf.org
Subject: Re: [dfdl-wg] Telcon Notes
 

Martin, 
            Please can you add a discussion of the semantics of DFDL 
Variables to the agenda of tomorrow's telecon. I have attached a document 
with some thoughts that I have had on the subject. 



Regards,

Geoff Judd
Websphere MQ Integrator Development
IBM UK Ltd
Hursley

Telephone:  +44-1962-818461
E-mail:           JUDDG at uk.ibm.com



"Westhead, Martin (Martin)" <westhead at avaya.com> 
Sent by: owner-dfdl-wg at ggf.org 
30/11/2005 18:12 


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<dfdl-wg at ggf.org> 
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Subject
[dfdl-wg] Telcon Notes
 


 
 




Present
-------
Mike Bekerle
Tara Talbott
Martin Westhead
Geoff Judd
Steve Hanson
Bob McGrath

Reports from Active Trackers
----------------------------

Scoping tracker is being worked on - no news.
Extensibility group is moving forward - nothing to report yet


Discussion of Geoff's documents
-------------------------------

Variables doc

Mike observed that variables could be used in place of his extensibility
proposal on annotations.

Martin asked about whether we wanted to include this in the standard. Is
the complexity worth the addition - the feeling of the meeting was
probably it was.

Martin proposed that instead of binding a variable value to an element,
the variable value should be set with an XPath expression. 

Discussed the question as to whether the variable value can be reset,
whether it can/should be scoped in the same way as annotation
attributes.

Next step will be for Geoff to revise the document to look at cases
where value may need to be reset and start to explore some of the
semantic issues involved.

Choices doc

Discriminator type - what if discriminator is not a string? For
efficiency can we handle discriminators that are integers?

Suggest that instead of discriminators being computed to strings they
are computed to an XPath value with its implied type so that numeric
discriminators do need to be converted to strings.

Wildcard docs

Group seemed fairly happy with this proposal as it stands. 


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