[DFDL-WG] Proposed Errata Language: Issue - DFDL Expressions may not return empty string for ...

[Steve Hanson]

Mike

I think you have highlighted a general deficiency in the spec. 

When a property is a DFDL String Literal, or List of DFDL String Literal, 
the spec is usually silent about the validity of empty string. The 
assumption has always been that empty string is only allowed when 
explicitly stated in the property description (such as for initiator, 
terminator and separator). Hence for textBooleanTrue/FalseRep, empty 
string is implicitly not permitted as a value. We should be explicit about 
this in section 6.3.1, and say empty string not allowed as a value, unless 
explicitly stated in the individual property description. That then covers 
us for the case where a property is a union of DFDL String Literal and 
DFDL Expression, as the rules for expression say it must return a value 
compliant with the property type. So the only properties that need to take 
your wording below are initiator, terminator and separator.

Is it a schema definition error or a processing error if an expression 
evaluates to something that does not comply with the type of the property? 
I don't think the spec says.

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:   16/01/2012 22:17
Subject:        Proposed Errata Language: Issue - DFDL Expressions may not 
return empty string for ...




Here's some proposed errata language:

The following properties descriptions are amended to include this 
stipulation: When a DFDL Expression is used, it may not produce empty 
string. 

The affected properties are:
textBooleanTrueRep
textBooleanFalseRep
initiator
terminator
separator

I did verify that the other properties that allow DFDL Expression to 
compute a string do not need further clarification. 

On Tue, Jan 10, 2012 at 11:52 AM, Steve Hanson <smh at uk.ibm.com> wrote:
Hi Mike 

As will be minuted, we agreed on the WG call today that we disallow 
expressions that return empty string for properties where empty string 
turns off the property. Please can you take a look through the spec and 
see if any properties other than initiator, terminator, separator are 
impacted, then I can complete the errata. 

(I would expect that inputValueCalc and outputValueCalc are not affected 
by this errata, as empty string is a legal value for the element in 
question if it is of type xs:string). 

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:        dfdl-wg at ogf.org 
Date:        10/01/2012 08:06 
Subject:        [DFDL-WG] spec clarification needed: is dfdl:terminator='{ 
...returns empty string ... }' allowed? 
Sent by:        dfdl-wg-bounces at ogf.org 





Let's use the example of terminator as a delimiter.

If I provide an expression so that I can compute terminator at runtime, is 
it allowed to return empty string? I.e., equivalent to writing 
dfdl:terminator="" which is effectively "turning off" use of terminator?

It seems very problematic to me if we allow this.  Nor do I think this 
generality is needed. 

We should clarify that for initiator/terminator/separator, if a runtime 
expression is used, then it must return at least one non-zero-length 
value. So using a runtime expression for a delimiter is effectively saying 
"yes there will be a delimiter", you are just not binding its specific 
value. 

I believe this runtime expression capability for delimiters was intended 
to allow the choice of the specific delimiter to be made based on data 
containing the value. This is common practice in data formats.

However, turning on/off whether delimiters are present or not, is not 
something I anticipated, and it has far bigger implications for the 
format. I mean you really can't decide much about the data format 
statically if even the existence of delimiters as part of the format or 
not can be postponed to runtime. 

Comments?

-- 
Mike Beckerle | OGF DFDL WG Co-Chair 
Tel:  781-330-0412
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 dfdl-wg mailing list
 dfdl-wg at ogf.org
 https://www.ogf.org/mailman/listinfo/dfdl-wg 





Unless stated otherwise above:
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-- 
Mike Beckerle | OGF DFDL WG Co-Chair 
Tel:  781-330-0412







Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number 
741598. 
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU





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