[DFDL-WG] DFDL and Multi-dimensional arrays - just say no to them?

[Mike Beckerle]

I'd like to solicit opinions on this suggestion:

We have 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. That is, the DFDL Schema's logical organization is 
constrained (heavily) by the data format.

We could take an exactly analogous position with respect to 
multi-dimensional or other complex arrays.

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 ordinary dense 
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. 

(I actually believe hiding sparse array implementations behind a 
dense-array facade is generally not advised. Algorithmically you must 
operate on the sparce representation anyway for efficiency. )

Suggested Conclusion: we can just say that we don't do multi-dimensional 
arrays because it is out-of-scope for us.

Comments?

...mikeb
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