[DFDL-WG] DFDL: Minutes from OGF WG call, 16 Nov 2007

[Ian W Parkinson]

Open Grid Forum: Data Format Description Language Working Group

Working Group Conference Call
14:00 GMT, 16 Nov 2007

Attendees
Mike Beckerle (IBM)
Geoff Judd (IBM)
Steve Hanson (IBM)
Suman Kalia (IBM)
Ian Parkinson (IBM)
Alan Powell (IBM)

1. Introduction
Mike called the meeting to discuss the revised Data Grammar portion of the 
DFDL specification, which he had previously circulated. This was discussed 
on the regular, weekly, conference call on 14th November, in Mike's 
absence. Mike will not be able to attend the next scheduled conference 
call.

2. Review of DFDL Data Grammar
The meeting discussed the following points:
As noted in the previous meeting, both the ComplexContent and 
ComplexElement productions include a "Prefix" element. Mike stated that 
this redundancy does exist in DFDL, but it sometimes necessary, e.g. for 
embedded groups. Steve suggested that, if this did need to be changed, we 
would do so with restrictions rather than a change to the productions.
Suman suggested that the present grammar specification does not 
satisfactorily cover the case where the start of an array needs to be 
aligned, with individual array elements automatically being aligned. Mike 
suggested that this can be dealt with, in a DFDL schema, by encapsulating 
the array in an element or sequence.This would require the author to build 
additional encapsulation around the array, which Suman felt would be 
unnatural, and suggested it would be more natural to introduce a property 
to explicitly deal with this situation. Mike observed that the XML 
specification treats arrays as simply adjacent elements, so we should 
minimize the number of properties which affect an entire array rather than 
each individual element. Mike and Suman will collaborate on a concrete 
proposal to address this.
Mike expressed discomfort with the use of "binary" and "opaque" to 
describe raw data, as these words ,ay be ambiguous. "opaque" in particular 
may refer to unparsed data, or to anyType elements. Suggested alternatives 
included "octets", "bits", "raw" and "blob".
The SequenceContent production currently contains a "finalUnused" element. 
Mike wondered whether this would best be moved to the Sequence production. 
Suman felt that there would then be issues with prefixes and suffixes. The 
meeting saw no good reason to change this.
Precedence order needs to be defined. Steve and Geoff will attempt to 
define a static order.
Regarding the query raised at the previous meeting concerning initial 
prefix Separators and final postfix Separators, Mike confirmed that these 
had been removed following comments in a previous draft of the document. 
They had originally been intended to support certain properties which 
could be now be defined using other features of the grammar.

Meeting closed 15:00 GMT


Ian Parkinson
WebSphere ESB Development
Mail Point 211, Hursley Park, Hursley, Winchester, SO21 2JN, UK





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