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@uk.ibm.com]
Sent: Thursday, March 27, 2008
2:02 PM
To: mbeckerle.dfdl@gmail.com
Cc: dfdl-wg@ogf.org;
dfdl-wg-bounces@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@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> |
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Date:
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26/03/2008 16:39 |
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Subject:
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[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 Powell/UK/IBM] --
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