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

Fri Nov 19 09:43:47 CST 2004

You are thinking along the lines I was; however, the challenge is that I
cannot find a way to do this using multilayer so I'm uncomfortable
suggesting that it's possible at all anymore. Here's some reasoning why.

In particular, it's the intersection of the induction across the items with
the first, middle*, last thing, and the spanning that seems to defy my
efforts to cut it up into progressive transformation layer by layer. In some
conversations I've referred to this problem as the "non-conforming trees"
problem. The fundamental shapes of the trees are not compatible, and
expressing the transformation between them isn't easily done via induction
of any kind on one or the other of the trees.

To me the First, Middle*, Last thing is very problematic. It's effectively a
little regular language (in the formal sense) that has to be recognized.
Generally this requires a finite-state-machine, and what makes FSMs
interesting and complex is always the way you diagnose malformed data in
addition to recognizing correct data. 

Now, a finite-state-machine is, to my mind, the ultimate procedural
abstraction, the quintessential opposite of "declarative" expression. To be
declarative about a FSM you end up saying "recognize this regular language",
and providing a description of the regular language, which is of course,
just begging the question of how it actually works. 

(And for us, we're not really talking about a regular language of character
text, but a pattern of usage in the binary data layout that obeys the
pattern of a regular language. So it's not like having a little regular
expression thing for validating text strings helps with this problem.)

I guess I'm arguing that a black box approach to this is not only
acceptable, but is highly likely to be the only "good" way to do it. In
light of this I've suggested a rep property called "streamFormat" (perhaps
should be renamed "recordFormat"), which gets values from the set VS, V,
VBS, FB, FBS, etc. etc. all these well-defined legacy data formats (there
are 19 of them I think).  In additon, one should be able to extend this by
introduction of a blackbox transformation.

And ... here's the rub...if that's true for this case, then other "hard"
examples like run-length encoding seem also in this category.  

There's several "leaps of faith" just made in these arguments, so i'd still
like people to take this "XML challenge" and see if there's some magic I'm
overlooking.

...mikeb

  _____  

From: Myers, James D [mailto:jim.myers at pnl.gov] 
Sent: Friday, November 19, 2004 9:52 AM
To: dfdl-wg at gridforum.org
Subject: RE: [dfdl-wg] simple way to study hard DFDL example problem - IBM
Format VS rec ords as XML

Without digging too much into the details, I'd say this is an example where
multi-layer comes in. The DFDL would describe a hidden layer in which the
first, middle, last data elements would be identified and put into a list,
and then that hidden list would be used as the input to create items in the
output layer.

I think this is conceptually similar to one of our run-length encoding
examples (more complex of course). If you read a sequence if ints and then a
sequence of floats and need to output a sequence of floats with int[i]
repeats of float[i], it would be easiest to create a hidden layer
representing the int and float sequences and to then produce output from
that. If you don't think about a layer, even this example gets painful - I
need to read an int, skip forward somewhere to find a float, skip back to
get the next int, etc.

Mike's full example, not starting with the XML-ized version, might be
something that requires more than one layer - read the original into
something with with XML schema Mike defines, then a layer making a sequence
of data elements, and then something that has the desired logical output.

I guess I would claim that this would not be too bad a way to describe a
fairly complex format in terms of a fairly different logical structure.
Whether one *should* do this in DFDL, or whether it would make more sense to
a) write a black box parser to get to items, or b) use DFDL to get to the
initial schema Mike wrote and use XSLT afterwards to convert to the desired
logical structure. I think there are enough cases where we need the
multilayer functionality in DFDL that are relatively simple that we have to
have it, which means it will then be possible to deal with complex
transformations in DFDL even if not simple/practical.

  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: Thursday, November 18, 2004 9:53 PM
To: dfdl-wg at gridforum.org
Subject: [dfdl-wg] simple way to study hard DFDL example problem - IBM
Format VS rec ords as XML

I've come up with a way to articulate the difficulties I'm having with DFDL
for complex file formats.

This problem may not be that hard for someone with more XML, XPath or XQuery
experience, so I'd apprecate it if you could look it over and if necessary
even run it by your resident XML experts.

In case the emailer mangles all the line lengths, I've also attached the
below as a file.

<!-- Example motivated by DFDL for IBM Format-VS -->
<!-- see http://tinyurl.com/3s2bq <http://tinyurl.com/3s2bq>  for details on
IBM Format-VS -->

<!-- Logically, our data is this: -->

<ITEM>The first item</ITEM>
<ITEM>This is the second item</ITEM>
<ITEM>The third</ITEM>

<!-- That is, data having this "logical" schema -->

<sequence>
  <element name="ITEM" type="string" minOccurs="0" maxOccurs="unbounded"/>
</sequence>

<!-- But the below is the input data were starting from. What you see below
simulates
     the structural issues of IBM Format-VS, but converting the problem into
an XML to XML
     transformation problem -->

<BLOCK>
  <SEGMENT>
    <WHOLE/> <!-- a WHOLE segment holds a whole item (Duh!). This element is
really a type tag. -->
    <DATA>The first item</DATA>  
  </SEGMENT>
</BLOCK>

<BLOCK>
  <SEGMENT>
    <FIRST/> <!-- a FIRST segment holds the first part of an item. -->
    <DATA>Thi</DATA>
  </SEGMENT>
</BLOCK>

<BLOCK>
  <SEGMENT>
    <MIDDLE/> <!-- a MIDDLE segment holds data from the center of an item
-->
    <DATA>s is t</DATA>
  </SEGMENT>
</BLOCK>

<BLOCK>
  <SEGMENT>
    <MIDDLE/> 
    <DATA>he sec</DATA>
  </SEGMENT>
</BLOCK>

<BLOCK>
  <SEGMENT>
    <LAST/> <!-- a LAST segment holds data from the end of the item.  -->
    <DATA>ond item</DATA>
  </SEGMENT>
  <SEGMENT>
    <WHOLE/><!-- This second segment in this block is a WHOLE segment.
However 
                 in general the 2nd segment of a block could be a WHOLE or
the 
                 FIRST segment of another multi-segment multi-block spanning
item -->
    <DATA>Third item</DATA>
  </SEGMENT>
</BLOCK>

<!-- The question: how can we express the transformation into the desired
logical form?
     Or is this beyond the call of duty for DFDL?
     Goals include to be as declarative as possible, and ideally, do it as a
set of
     XML Schema annotations in the GGF DFDL style.  --> 

<!-- here's an XSD (untested) for the input data structure -->

<complexType name="Format_VS_t">
 <sequence>
   <element name="BLOCK" type="Block_t" minOccurs="0"
maxOccurs="unbounded"/>
 </sequence>
</complexType>

<complexType name="Block_t">
      <sequence>
         <element name="SEGMENT" type="Segment_t" minOccurs="1"
maxOccurs="2"/>
      </sequence>
</complexType>

<complexType name="Segment_t">
 <sequence>
  <choice>
    <element name="WHOLE">
    </element>
    <element name="FIRST">
    </element>
    <element name="LAST">
    </element>
    <element name="MIDDLE">
    </element>
  </choice>
  <element name="DATA" type="string"/>
 </sequence>
</complexType>

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