Hi all,
I've just noticed - I didn't distribute
the minutes from last week's WG call. Apologies for the delay.
Cheers,
Ian
Open Grid Forum: Data Format Description
Language Working Group
Weekly Working Group Conference Call
16:00 GMT, 30 Apr 2008
Attendees
Mike Beckerle (Oco)
Steve Hanson (IBM)
Ian Parkinson (IBM)
Alan Powell (IBM)
1. F2F meeting at IBM Hursley
Mike has confirmed that he will travel
to IBM Hursley to further design discussions with the IBM team, later in
May.
2. Review of specification line items
The meeting began a review of the outstanding
work required for specification draft 32, but this was not completed during
the meeting as a number of technical discussions were triggered.
- valueCalc Mike has provided material
to Alan. No further work is anticipated on this item.
- nulls/defaults/optionals There
has been some discussion on nilIndicatorPath and forward references, and
this discussion needs to continue. The rest of this section is now complete.
- UML description of schema components
complete
- Property Precedence This item
is currently marked complete; however it has sparked some discussion. On
unparse, if the infoset contains less than the required number of occurances
of some field, then the unparser may be expected to output sufficient instances
of the default value. We need to craft a policy to determine exactly how
this achieved; for example, do we use the xsd:minOccurs value or do we
try to match the result of the dfdl:occurs expression? Mike proposed that
if an occurs expression is present, it must evaluate to a valid number
of occurances. Steve suggested that we disambiguate dfdl:occurs from xsd:minOccurs
and xsd:maxOccurs by renaming the property dfdl:occursPath - however, this
property can be an expression involving calculations, not just a simple
path. A number of simplifications have been proposed, and these require
further discussion.
Alan noted that an XPath expression
has no way to access a field's default value, and suggested introducing
a function to handle this. Also, we may need to define count() such that
it returns the number of instances of an element after any necessary padding
and introduce a different way to obtain the number of instances found in
the infoset.
Stop values and terminators are not
considered part of the logical data.
Steve will update the diagram.
- Variable Markup Steve had previously
proposed a scheme whereby properties, such as iniitator or terminator,
could be described by another DFDL element or type definition. We could
use a similar mechanism to handle strings with embedded complex structures.
This subject will be tackled during the F2F.
- Regular Expressions for Lengths
The meeting agreed to adopt the regular expression subset previously distributed
by Alan. Regular expressions are ignored for unparsing, and are only used
to determine the length of an element during parsing. Considering repeating
elements, Steve contrasted the behaviour of regular expressions in DFDL
(where the regular expression matches just a single instance) with that
in IBM's MRM technology (where a regular expression matches the entire
array), and the meeting discussed whether a regular expressions should
include any necessary terminators.
Meeting closed, 17:10 GMT
Ian Parkinson
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