Mike

I don't think your proposal to use lengthkind 'As-If-Implict' on unparsing works as described.

Lengthkind = 'implicit' means get the fixed length from the length/maxLength facet whereas your description says the dfdl:representational-length is computed from the logical value.

The two cases to consider are when the field is padded or not.

When not padded then taking the infoset value as is seems reasonable if the length is not already known
When padding is required then an 'output length' must be specified somewhere.

Case 1 no padding (your example)
The problem is how does dfdl:representational-length know that the length is not already know?
dfdl:length= '10' should return 10
dfdl:length= '{10}' should return 10
dfdl:lentgh= '{../len}' should return ? value from infoset?

Case 2 Padding

There needs to be an output length specified.
You could explicitly set a value in the len field <element name=len dfdl:outputValuCalc= 10 />
We could use the length/maxlength facet as the place to specify the 'output length' but I would prefer an explicit dfdl property.
Alternatively we could say that padding is not used and take what is in the infoset.

Alan Powell

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

From:	"Mike Beckerle" <mbeckerle.dfdl@gmail.com>
To:	<dfdl-wg@ogf.org>
Date:	24/05/2009 00:39
Subject:	[DFDL-WG] Action 029 outputValueCalc, variables (& also contribution for 026 - env. and payload)

Finally, here's a draft document about outputValueCalc, unparsing, and, variables, and such.

Also attached is a zipped eclipse project containing two subdirs: outputValueCalc has examples of ... outputValueCalc, and variables has an envelope payload example enhanced and corrected somewhat over a prior one I sent.

There's one entirely new concept here. I added an attribute to dfdl:defineVariable to specify whether the variable is for input (parsing) or output (unparsing). I was unable to get things to work in any simple manner without separating the two classes of variable. This doesn't seem too bad actually.

...mike

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