[DFDL-WG] MBTK and Daffodil - Intentioning Violating Property Scoping Rules?

[Tim Kimber]

OK. I'll bite...

Some features of DFDL take some time to understand, and some are not 
perfectly described in the specification. That does make it hard for 
somebody in your position because you only have the specification to go 
on, As far as I'm concerned, you should feel free to raise questions like 
this without apology.

In this case, neither Daffodil nor IBM DFDL is violating the (intended) 
rules in the specification. The properties from the imported xsd are not 
being used by a *component* in the main xsd. Instead, the 'ref' attribute 
of the global format block in the main xsd is referring to a named format 
block in the imported xsd. In this way, the library xsd is contributing a 
wide-ranging list of default values into the global format block of the 
main xsd.

I expect Steve or Mike will add some details to that...

regards,

Tim Kimber, DFDL Team,
Hursley, UK
Internet:  kimbert at uk.ibm.com
Tel. 01962-816742 
Internal tel. 37246742




From:   "Garriss Jr., James P." <jgarriss at mitre.org>
To:     "dfdl-wg at ogf.org" <dfdl-wg at ogf.org>, 
Date:   25/04/2013 15:00
Subject:        [DFDL-WG] MBTK and Daffodil - Intentioning Violating 
Property        Scoping Rules?
Sent by:        dfdl-wg-bounces at ogf.org



(Emotions are hard to convey in email; please trust me when I say that I 
am writing this email with kindness and friendliness!)
 
In section 8 it says, “The dfdl:format annotation on the top level 
xs:schema declaration provides defaults for the DFDL representation 
properties at every DFDL-annotatable component contained in the schema 
document. They do not apply to any components in any included or imported 
schema document (these may have their own defaults).”
 
If I understand this, it means that when properties are defined using 
<dfdl:format> in one DFDL schema file, they are out of scope for any other 
DFDL schema file. 
 
So if schema A defines some properties and includes schema B, the 
properties are out of scope in schema B.
Similarly, if schema A includes schema B and schema B defines some 
properties, the properties are out of scope in schema A.
 
Is that right?  I think so, and I have empirically confirmed this in both 
tools.
 
Ok, so you know where this going, right?  Why does the following line 
work?
 
<xsd:import namespace="http://www.ibm.com/dfdl/GeneralPurposeFormat" 
schemaLocation="IBMdefined/GeneralPurposeFormat.xsd"/> 
 
According to the spec, it shouldn’t.  Yet both tools support it. 
 
But if you make any changes to the GeneralPurposeFormat, it breaks.  You 
can’t rename it.  You can’t put it in a different folder.  Etc.
 
Here’s what I suspect:  Both MBTK and Daffodil hard-coded this as an 
undocumented exception to the rule. 
 
I think you want to have your cake (properties are out of scope) and eat 
it, too (except when we want them to be in scope because repeating all the 
properties in every DFDL file is a pain).
 
If I’m wrong, just let me know.  It’s entirely possible that I don’t 
really understand what’s going here.
 
But if I’m right, then you guys should not do this.
 
·       If the spec makes sense, then you should follow the spec.
·       If the spec doesn’t make sense, then you should change the spec.
·       If the spec needs an exception to the rule for this one case, then 
add an exception and follow it.
 
To intentionally break the spec in an undocumented fashion seems wrong.--
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