[DFDL-WG] DFDL: Minutes from OGF WG call, 09 Apr 2008

[Ian W Parkinson]

Open Grid Forum: Data Format Description Language Working Group

Weekly Working Group Conference Call
16:00 GMT, 9 Apr 2008


Attendees
Mike Beckerle (Oco)
Steve Hanson (IBM)
Ian Parkinson (IBM)


1. OGF 23 and Face-to-Face meetings
As DFDL was represented at OGF 22, we will skip OGF 23 (to be held in 
Barcelona). OGF 24 will be held in Singapore in September. Previous 
meetings have not attracted much interested in DFDL - Mike suggested that 
interest will pick up as we complete the specification and have 
implementations under way. DFDL was originally initiated by the OGF's 
Database Access and Integration Services project (DAIS), and Steve 
wondered whether this project still has a requirement and interest in 
DFDL.

Mike has the opportunity to visit IBM Hursley, in the UK, to focus on 
progressing the specification in collaboration with the IBM working group 
members. This is tentatively scheduled for Monday June 2nd - Thursday June 
4th.

2. Decimal supplement
Discussion on the DFDL-WG mailing list raised a question: should 
TextNumberFormat, BinaryNumberFormat and FloatNumberFormat be left as 
separate properties, or combined into a single property with a greater 
selection of possible values? The meeting agreed that it is better to keep 
these as separate properties.

The meeting reviewed the current distinction between binary coded decimal 
(BCD) and packed decimal, and agreed that the BCD format is never signed, 
while the packed decimal format always has a sign nibble. The "unpacked 
decimal" format, discussed on the mailing list, will remain unsupported 
for DFDL v1.0, but could be added later. Mike asked whether we should 
consider renaming the "decimalVirtualPoint" property to reflect the use of 
commas in many locales, perhaps "decimalVirtualSeparator" - the consensus 
was that this is unnecessary.

3. Regular Expressions
A full review of the regular expressions proposal will wait until Alan can 
be present on a working group call. The proposal states that it represents 
a subset of XML schema's regular expression lanaguage, and it may be 
useful to identify features which are omitted.

It may be useful, in a regular expression, to be able to use DFDL entity 
references to provide for byte sequences that are not subject to codepage 
conversion. Although Steve felt this not to be a requirement, Mike thought 
it difficult to justify such an omission.

4. Calculated Values
Mike's document covering the use of inputValueCalc and outputValueCalc has 
undergone some revisions following discussion on the mailing list. The 
current (v3) draft contains a small error in the title of section 1.2.

In cases where an element is not hidden, but has an outputValueCalc, it is 
currently not clear whether the outputValueCalc result takes precedence 
over any value present in the InfoSet. After some discussion, the group 
agreed that if such an element is present in the InfoSet, it must have the 
same value as the result of the calculation. An unparser should check this 
and fail the unparse if there is a mismatch.

5. Forward References
The nilIndicatorPath, occursPath and lengthPath introduce a form of 
forward referencing, which had previously been outlawed by DFDL. This can 
make it difficult for a DFDL parser/unparser to implement streaming 
efficiently.

Mike observed that there are likely to be a number of data formats which 
require a limited amount of forward referencing, such as record-based 
formats which involve a certain amount of "random access" in an individual 
record. He suggested that the restriction on forward references be lifted, 
with the caveat that mis-use of this feature can effectively prohobit 
streaming. This can further be discussed when Alan is available, as it 
affects the DFDL expression language.

Meeting closed, 16:50 GMT




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





Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number 
741598. 
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU





-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.ogf.org/pipermail/dfdl-wg/attachments/20080410/9439fbfa/attachment.html