[DFDL-WG] DFDL: Minutes from OGF WG call, 16 Nov 2007
Ian W Parkinson
PARKIW at uk.ibm.com
Mon Nov 19 10:55:00 CST 2007
Open Grid Forum: Data Format Description Language Working Group
Working Group Conference Call
14:00 GMT, 16 Nov 2007
Mike Beckerle (IBM)
Geoff Judd (IBM)
Steve Hanson (IBM)
Suman Kalia (IBM)
Ian Parkinson (IBM)
Alan Powell (IBM)
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
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
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