[DFDL-WG] Telcon minutes 2006-09-20

[Mike Beckerle]

Attendees: Mike Beckerle, Bob McGrath, Geoff Judd

Agenda:
Report on OGF DFDL session last week
Discuss ongoing document edits. 
Review ongoing actions:
 
Action: [Geoff] Put together a first pass description
Action: [Mike] Look at DCGs
Action: [Tom] Modifications to the scoping section.

Discussion of next steps with multidimensional arrays

Report on DFDL session at OGF last week: 
- only 6 people attended, of them only 2 were "new people", one from 
Boeing, one  from National Archives.  Presentation was uneventful.

Doc Edits:
- Geoff Judd reports that uncertainty topic has been split into core + 
supplement and the results posted on GridForge. The defaults and nulls 
split is still being figured out. Unclear how to split it up, what stays 
core, etc.
- Tom Sugden had scoping reorg - Not on call, no report.

Ongoing Actions
- Geoff has written up an example of a group description. Still under 
review/discussion with Mike and Martin
- Mike has taken a stab at starting a complementary more methodical 
description. To circulate to Geoff and Martin first.
- Mike grabbed some material on Definite Clause Grammars. Seems to have 
potential as a formalism for us. The issue is that DCGs are actually 
programs, i.e., they're runnable when crafted in the usual way, hence, one 
would expect to have to put in all the details. That is, DCGs as a 
notation aren't naturally used as a summarization which hides complexity, 
but rather to make all the complexity explicit. Conclusion, we need to try 
using them and see how it works out.

MultiDimensional Arrays
- we reviewed the status of the work on multidimensional arrays. 
- we had been assuming we needed more than just 1d array support, but this 
is now unclear. We've pushed back on "top-down" use of XML Schemas, i.e., 
DFDL must be used bottom up, and transformation into the "logical form you 
wanted" is not our job. With respect to multi-dimensional arrays having 
complex implementations we can adopt the exact same position. The DFDL 
describes the representation, and the sttructure of the DFDL schema will 
end up matching the shape of the representation of the array. Transforming 
that into something that looks and acts like a multi-dimensional array is 
a transformation that is out-of-scope for us. E.g., if the array is stored 
as a run-length encoded vector, then it is DFDL's job to describe this 
run-length encoded vector, but not to project/transform it so that it can 
be accessed in a manner that hides the run-length encoding and makes it 
look like an ordinary dense array. 
- Mike agreed to write this point up and put it before the WG on our email 
list.


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