[DFDL-WG] DFDL: Calculated Values section rewrite

[Mike Beckerle]

Re: no proper description of prefixed. Recall that last Nov we discussed
lengthKind='prefixed'. See
http://www.ogf.org/pipermail/dfdl-wg/2007-November/000667.html

 

This eliminates the keywords for prefix types and lengths of prefix fields.
We just introduce predefined types like dfdl:prefix2 and dfdl:prefix4 which
are very keyword-ish names.

 

I guess this material is pending for inclusion into the spec still.

 

Now back to our regularly scheduled email reply...

 

I've attached a revised calculated value properties doc which incorporates
suggestions from Alan, specifically, there's a new example, which is a 2-d
array with nrows, ncols fields stored before it. I think this motivates the
connection between outputValueCalc, and number of occurrences and occurs
calculations nicely.

 

.mikeb

 

  _____  

From: Alan Powell [mailto:alan_powell at uk.ibm.com] 
Sent: Thursday, March 27, 2008 2:02 PM
To: mbeckerle.dfdl at gmail.com
Cc: dfdl-wg at ogf.org; dfdl-wg-bounces at ogf.org
Subject: Re: [DFDL-WG] DFDL: Calculated Values section rewrite

 


Mike 

A couple of comments on the using derived/representation nomenclature with
OutputValueCalc and a couple of minor corrections. 

However I thought the Length Prefix example a bit odd as I would have
expected a single HexBinary element rather than an array of bytes. 

And that got me thinking why isn't it just LengthKind=prefixed but I
discovered that there is no proper description of prefixed. Was it intended
to cover different kinds of length prefix or is it assumed to be 2 (or 4)
bytes? 





Alan Powell

MP 211, IBM UK Labs, Hursley,  Winchester, SO21 2JN, England
Notes Id: Alan Powell/UK/IBM     email: alan_powell at uk.ibm.com  
Tel: +44 (0)1962 815073                  Fax: +44 (0)1962 816898





From: 

"Mike Beckerle" <mbeckerle.dfdl at gmail.com> 


To: 

<dfdl-wg at ogf.org> 


Date: 

26/03/2008 16:39 


Subject: 

[DFDL-WG] DFDL: Calculated Values section rewrite

 

  _____  




My deliverable for the next draft (32) was to revise the calculated values
section. 
  
I have rewritten it and the draft is attached. 
  
Of note: I have removed the troublesome "outputLengthCalc" property, as I no
longer see a critical need for it. One of the examples computes the number
of occurrences for a byte array, and I think that mechanism along with
alignment is sufficient to handle the troublesome cases I was considering
where size of padding had to be dynamically computed. 
  
The section now consists of a short table of definition, followed by
illustrative examples, however, I think this is fine. The semantics of
inputValueCalc and outputValueCalc aren't really that complex. They can be
described in a paragraph. It is the motivation for them that is complicated,
so I think examples in the spec, while sometimes considered problematic, are
OK in this case. 
  
  
  
 [attachment "calculated-value-properties.doc" deleted by Alan
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