[dfdl-wg] simple way to study hard DFDL example problem - IBMFormat VS rec ords as XML

[Myers, James D]

I think we at least agree in practice that there's a limit on how
complex a transform you'd want to code in DFDL logic. Not sure if we
agree on whether it is possible.

As for LR parsers - I'm not a parser guy, but I just looked at the
wikipedia entry :-) :

Seems like a simple enough concept - if you let me have layers, and I
can use information in those layers to select choices for further
processing, can you stop me from making an LR parser (or doing what an
LR parser does)? I've got a stack, and choices let me specify an action
table... In the same way that if you give me layers (or variables),
addition, and for loops, you can't stop me from doing multiplication.
And if you require those  things for other reasons but don't need
multiplication, you can't really talk about excluding multiplication
from the language design. You can say that we won't worry about
multiplcation examples or how easy it is to write them down or what
performance you'll get trying to run them and suggest that you plug
something in to handle them directly though, and this is probably what
we need to do in DFDL.

I may still be missing something and there is a piece of functionality
that we haven't identified a need for that would be needed for an LR
parser/our pathological examples, but I guess I'm getting more convinced
that our primitives are sufficiently powerful that they can be
used/abused to do all of the complex things that have come up. I'm not
sure how we can close the issue - specify the map from DFDL primitives
to LR parser as I started to above, or find an example known to require
LR parsing and work it? Or?

  Jim



> -----Original Message-----
> From: owner-dfdl-wg at ggf.org [mailto:owner-dfdl-wg at ggf.org] On 
> Behalf Of mike.beckerle at ascentialsoftware.com
> Sent: Friday, November 19, 2004 11:36 AM
> To: smh at uk.ibm.com; dfdl-wg at gridforum.org
> Subject: RE: [dfdl-wg] simple way to study hard DFDL example 
> problem - IBMFormat VS rec ords as XML
> 
> 
> I believe you and Jim are actually disagreeing. Jim is saying 
> he's still optimistic that this transformation, even though 
> complex, can be expressed directly in DFDL. You are saying 
> this would require XSLT or a Java program or whatever to do it.
> 
> > 
> > Mike you say you are aware of 19 such legacy formats, and I
> > bet there are more. Well IBM's broker has no specific support 
> > for any of these, nor have we been asked to incorporate them 
> > into our message model. Maybe we should play the percentages 
> > game - if we see enough different subsystems that use the 
> > same cryptic format then it becomes worth building the 
> > support into DFDL.
> > 
> 
> Ascential supports 6 or 7 of these formats today. Batch systems will
> encounter this more than online. You get them when a 
> mainframe job writes
> out a tape on a mainframe, and then you read that tape on a 
> unix tape drive
> either directly or first into a file. Alternatively, you pick 
> up a mainframe
> file via FTP or some such and directly operate on it on other systems.
> Mainframe software handles all the VS block and and such 
> stuff in the lower
> layers as you know (not to mention the tape label) unix 
> software does none
> of this, you just get the raw bytes.
> 
> My point is not as much about these 19 or more particular 
> formats, but the
> issue of how much complexity we go after.
> 
> In the past we've looked at things like logical arrays with
> run-length-encoded representations and the suggestion has 
> been there that
> DFDL might be able to directly express this transformation 
> without need to
> go outside DFDL. 
> 
> I've come to believe there are certain limits to this 
> complexity and I think
> perhaps tree-shape compatibility is at the core of them. 
> Building a DFDL
> description for data that ultimately requires an LR(k) 
> sophistication parser
> to correctly interpret the data is clearly a non-starter it 
> seems. Where
> this line is drawn is important. 
> 
> ...mikeb
> 
> 
> 
> 
> ...mikeb
> 
>