[DFDL-WG] clarification on when escape characters are needed

Wed Jun 19 08:47:19 EDT 2013

James

I don't see how an escape scheme helps here.  The "f82+=7&%q" is all data, 
there's no escape character. 

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:   "Garriss Jr., James P." <jgarriss at mitre.org>
To:     Steve Hanson/UK/IBM at IBMGB, Mike Beckerle 
<mbeckerle.dfdl at gmail.com>, 
Cc:     "dfdl-wg at ogf.org" <dfdl-wg at ogf.org>
Date:   19/06/2013 12:33
Subject:        RE: [DFDL-WG] clarification on when escape characters are 
needed

> The DFDL 1.0 spec implies the behaviour where you get…

If this is the direction the WG goes, can you please make this explicit 
rather than implicit?  Using Mike’s excellent example below would go a 
long way to making the issue clear. 

As for a solution, would it not be better to use an escape scheme, like 
this?

<sequence dfdl:separator="=" dfdl:separatorPosition="infix">
  <element name="a" type="xs:string"/>
  <element name="b" type="xs:string" 
dfdl:escapeSchemeRef="DefaultPropertiesEscapeScheme"/>
</sequence>

(Cred to Taylor)

If so, it would be helpful to include that in the example.

From: dfdl-wg-bounces at ogf.org [mailto:dfdl-wg-bounces at ogf.org] On Behalf 
Of Steve Hanson
Sent: Wednesday, June 19, 2013 5:29 AM
To: Mike Beckerle
Cc: dfdl-wg at ogf.org
Subject: Re: [DFDL-WG] clarification on when escape characters are needed

The DFDL 1.0 spec implies the behaviour where you get: 

<a>password</a> 
<b>f82+</b> 

followed by a processing error.  There is no special casing of the last 
element in the group. 

Changing the model to the following achieves the desired infoset: 

<sequence dfdl:separator="=" dfdl:separatorPosition="infix">
  <element name="a" type="xs:string"/>
  <sequence dfdl:separator="">
    <element name="b" type="xs:string"/>
 </sequence>
</sequence>

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:        Tim Kimber/UK/IBM at IBMGB 
To:        dfdl-wg at ogf.org, 
Date:        19/06/2013 09:37 
Subject:        Re: [DFDL-WG] clarification on when escape characters are 
needed 
Sent by:        dfdl-wg-bounces at ogf.org 

In the IBM implementation we have taken the view that the separator 
defines the format for all of the group's content. That means that all 
separators are counted as being significant, even if they occur within the 
content region of the final group member. 
I agree that other interpretations are possible - the MRM parser in 
earlier versions of WebSphere Message Broker takes an infix separator out 
of scope when it encounters the final declared child of a group. 

I intend to address this point when I write up the rules for matching 
string literals and delimiters. 

regards,

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

From:        Mike Beckerle <mbeckerle.dfdl at gmail.com> 
To:        dfdl-wg at ogf.org, 
Date:        19/06/2013 03:52 
Subject:        [DFDL-WG] clarification on when escape characters are 
needed 
Sent by:        dfdl-wg-bounces at ogf.org 

Suppose I have a sequence. It has an infix separator which is "=".

<sequence dfdl:separator="=" dfdl:separatorPosition="infix">
  <element name="a" type="xs:string"/>
  <element name="b" type="xs:string"/>
</sequence>

Now, consider this data:

password=f82+=7&%q

I want 

<a>password</a>
<b>f82+=7&%q</b>

Notice how the b element contains an '=' which was not escaped in any way 
in the sequence. Element b is statically known to be last, the separator 
is infix; hence, things are unambiguous even if there is no escaping.

However, there is an alternative interpretation, which is that the above 
data should fail, because it produces <a>password</a><b>f82+</b> but then 
does not find the expected stuff next. Rather it finds the '=7&%q' data. 
In other words, the sequence separator divides the sequence content into 3 
content regions, but there aren't 3 things to consume those, so it is a 
processing error. 

Which is correct? 

-- 
Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | 
www.tresys.com
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741598. 
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