[DFDL-WG] DFDL: Calculated Values section rewrite

Thu May 15 11:51:27 CDT 2008

Mike

I have added this to the spec doc with some minor changes shown in 
attached.

Two new questions 

I assume in/outvalueCalc are not allow on arrays
dfdl:hidden prevents elements appearing in the infoset on parsing but 
there isn't an equivalent to prevent infoset elements appearing in the 
data stream on unparsing. We have assumed that inputvalueCalc prevents 
output but is that always the case? (Steve you need to add InputValueCalc 
to unparsing property precedence). If inputValueCalc is sufficient to 
prevent output couldn't outputvalueCalc prevent input rather than hidden?

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:
Steve Hanson/UK/IBM at IBMGB
Cc:
dfdl-wg at ogf.org
Date:
09/04/2008 15:03
Subject:
Re: [DFDL-WG] DFDL: Calculated Values section rewrite

Hmm. We?re in this situation where DFDL is so rich with features that 
anything those features don?t handle will by definition be an obscure 
corner case thereby hard to motivate.

I can change this example to use three single byte binary integers instead 
of 6 packed decimal digits. This is certainly a feasible binary data 
format, though it?s nothing I?ve ever seen. It also makes the example 
orthogonal to the decimal changes, so generally is more on point.

Attachment is new example plus the other improvements suggested.

From: Steve Hanson [mailto:smh at uk.ibm.com] 
Sent: Wednesday, April 09, 2008 9:29 AM
To: mbeckerle.dfdl at gmail.com
Cc: dfdl-wg at ogf.org
Subject: Re: [DFDL-WG] DFDL: Calculated Values section rewrite

Comments from Ian and Steve: 

1) Is it a schema error if default/fixed attributes specified along with 
dfdl:inputValueCalc and/or dfdl:outputValueCalc? 

2) 2D array. 
- dfdl:occurrences() is not in the expression language in draft 031. Is 
something missing from the language, or should the XPath count() function 
be used here? 
- $dfdl:occurrences - $ not needed 
- dfdl:outputValueCalc for 'ncols' - we think the else clause should be 
'..\rows[1]\cols' 

3) PD date 
- As an example, it's perhaps not a good one as we have 
decimalCalendarFormat as a property of a decimal number, which is intended 
to do exactly this 
- As it stands, it will need updating to reflect latest decimal supplement 

Regards, Steve

Steve Hanson 
Programming Model Architect
WebSphere Message Brokers
Hursley, UK
Internet: smh at uk.ibm.com
Phone (+44)/(0) 1962-815848 

"Mike Beckerle" <mbeckerle.dfdl at gmail.com> 
Sent by: dfdl-wg-bounces at ogf.org 
09/04/2008 02:44 

Please respond to
mbeckerle.dfdl at gmail.com

To
Alan Powell/UK/IBM at IBMGB 
cc
dfdl-wg at ogf.org, dfdl-wg-bounces at ogf.org 
Subject
Re: [DFDL-WG] DFDL: Calculated Values section rewrite

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. 

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. 

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