[DFDL-WG] OGF DFDL WG minutes 2007-12-05 call
Mike Beckerle
beckerle at us.ibm.com
Wed Dec 5 17:21:01 CST 2007
OGF DFDL WG minutes 2007-12-05 call
Suman Kalia, Simon Parker, Alan Powell, Mike Beckerle
(who else? - was someone else on also)
We discussed
Output issues in the DFDL expression language:
E.g.., an outputValueCalc for a field in the header of a data stream may
contain information that requires you to know the rep, or length of the
rep, of the whole data item.
We concluded that this kind of thing can't be ruled out. Some formats just
require buffering and are not streamable; however, implementations can
vary on just how large a data item they're able to cope with here.
Expression language section will include a subsection highlighting this
issue and that implementations can vary here.
Alan will update his expression language proposal and include this.
Also suggested was a path length-from-to function that takes 2 path
expressions and gives you the size of the represntation between them.
(start of first, to last bit before start of 2nd).
(I don't think we discussed a clear use case motivating this, but there
may be one. We did discuss applications trying to fit data into limited
size boxes, but the use case is not clear.
Also note that all representation lengths are subject to change due to
different starting alignments.)
Nillable and Default:
We also discussed the interaction of nillable and having a default.
The sense of the group on the call is that we can restrict these so that
if something is nillable it cannot also have a default value, and that the
behavior of DFDL on output for a required element that is nillable but not
in the logical data, is to create a null value. Everyone agreed that there
is no need for a property useNullValueForDefault because this should
always be the behavior.
Mike will forward a proposal.
...mikeb
Mike Beckerle
STSM, Architect, Scalable Computing
IBM Software Group
Information Platform and Solutions
Westborough, MA 01581
direct: voice and FAX 508-599-7148
assistant: Pam Riordan
priordan at us.ibm.com
508-599-7046
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