[DFDL-WG] Issue 168 - Re: Fw: Escape scheme properties that can be expressions

Thu Apr 5 07:44:44 EDT 2012

Mike

I think the wording in 6.3.2 applies specifically to the anonymous 
dfdl:format. I don't think it was intended to apply to dfdl:format inside 
dfdl:defineFormat nor to dfdl:escapeScheme inside dfdl:defineEscapeScheme, 
presumably due to the reasons we discussed on last week's call - namely 
that by using dfdl:ref they can be applied directly to a specific object. 
Of course, dfdl:ref can be used on the anonymous dfdl:format too,  So the 
6.3.2 words should have said:

"In the dfd:format annotation on the xs:schema, a DFDL property either 
declared locally or obtained via dfdl:ref and which uses a DFDL 
expressions to provide its value MAY NOT contain relative paths".

So I think we still need to decide on dfdl:format inside dfdl:defineFormat 
nor to dfdl:escapeScheme inside dfdl:defineEscapeScheme.

Regards

Steve Hanson
Architect, 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:     Steve Hanson/UK/IBM at IBMGB
Cc:     dfdl-wg at ogf.org
Date:   03/04/2012 15:45
Subject:        Issue 168 - Re: [DFDL-WG] Fw: Escape scheme properties 
that can be expressions

In the absence of a compelling reason to allow relative paths here, I 
think the conservative choice is to retain this rule from 6.3.2.

However, I did think about this and my evaluation on this topic is that 
allowing relative paths makes things just a little more complicated 
analytically to insure one gets good performance, but as DFDL does not 
allow recursive types, it is a relatively simple analysis to convert any 
relative path use in DFDL into absolute paths. So I am not worried about 
there being performance impact. 

...mikeb

On Mon, Apr 2, 2012 at 7:30 AM, Steve Hanson <smh at uk.ibm.com> wrote:
We took action 168 on the last call to discuss the issue of relative paths 
in expressions for properties in global formats. 

168
Relative path expressions in global annotations (Mike) 
28/03: Mike to check that allowing relative paths does not cause 
performance problems for an implementation. 
05/04:

Just seen this in section 6.3.2. of the spec:  "DFDL expressions that are 
used to provide the value of DFDL properties in the dfd:format annotation 
on the xs:schema MAY NOT contain relative paths". 

Regards

Steve Hanson
Architect, Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848 
----- Forwarded by Steve Hanson/UK/IBM on 02/04/2012 12:28 ----- 

From:        Steve Hanson/UK/IBM 
To:        dfdl-wg at ogf.org 
Date:        14/03/2012 16:09 
Subject:        Escape scheme properties that can be expressions 

The spec allows the escapeCharacter and escapeEscapeCharacter of DFDL 
escapeScheme to be expressions, in case the characters are supplied 
dynamically in the data stream. 
However given that escape schemes are defined globally, should these 
properties be permitted to take relative paths in the expression?   
Today the spec implicitly allows this, meaning an implementation can not 
entirely validate an escapeScheme annotation up front, but must validate 
escapeCharacter and escapeEscapeCharacter at each point of use. 
I'm not sure it makes much sense for the path to be anything than 
absolute. 

Regards

Steve Hanson
Architect, Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848

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