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@uk.ibm.com
tel:+44-1962-815848



From:        Mike Beckerle <mbeckerle.dfdl@gmail.com>
To:        dfdl-wg@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@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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