Allowing dfdl:lengthKind on choices
has other benefits. It means that elements, sequences and choices are consistent
in how they are capable of being extracted (literal length, XPath, model
determined, prefixed, null terminated).
I don't think unresolvableWhenParsing
implies fixed length storage. I could have an unresolvable choice being
two variable length strings, terminated by the terminator of the choice.
Regards, Steve
Steve Hanson
WebSphere Message Brokers
Hursley, UK
Internet: smh@uk.ibm.com
Phone (+44)/(0) 1962-815848
| Mike Beckerle/Worcester/IBM@IBMUS
20/11/2007 21:23
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To
| Steve Hanson/UK/IBM@IBMGB
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cc
| dfdl-wg@ogf.org
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Subject
| Re: [DFDL-WG] Grammar as adapted to
infosetLink |
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Rather than overloading "implicit"
length to mean this, I think we need an enum-valued property for choices.
Today there is this choiceUnresolvableWhenParsing
boolean. I think this shoudl become choiceType="unresolvableWhenParsing".
Then we can have an enum value for the
case where all arms of the choice are assumed to be padded to max
length of the alternative.
So I think we have 3 enum values:
variableLength
fixedLength
unresolvableWhenParsing
variableLength means the storage taken
depends on the alternative selected, Fixed length means shorter alternatives
are padded to the length of the longest. unresolvable means what it means
now, which is that you can't tell which variant it is (which also implies
the storage required is fixed length).
...mikeb
Mike Beckerle
STSM, Architect, Scalable Computing
IBM Software Group
Information Platform and Solutions
Westborough, MA 01581
direct: voice and FAX 508-599-7148
assistant: Pam Riordan
priordan@us.ibm.com
508-599-7046
| Steve Hanson/UK/IBM@IBMGB
11/19/2007 07:13 AM
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To
| Mike Beckerle/Worcester/IBM@IBMUS
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cc
| dfdl-wg@ogf.org
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Subject
| Re: [DFDL-WG] Grammar as adapted to
infosetLink |
|
Or allow xs:choice to carry dfdl:length
& dfdl:lengthKind. Then lengthKind="implicit" could
mean the length is the longest of the modelled alternatives.
Regards, Steve
Steve Hanson
WebSphere Message Brokers
Hursley, UK
Internet: smh@uk.ibm.com
Phone (+44)/(0) 1962-815848
| Mike Beckerle/Worcester/IBM@IBMUS
16/11/2007 19:29
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To
| Steve Hanson/UK/IBM@IBMGB
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cc
| dfdl-wg@ogf.org
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Subject
| Re: [DFDL-WG] Grammar as adapted to
infosetLink |
|
There are of course alternatives.
E.g., a hidden or non-hidden field which
is a byte array or hexBinary to absorb the padding bytes at the ends of
the shorter variants. Or one could put trailing skip bytes on the last
element or group of each of the shorter variants.
One can also encapsulate the whole choice
in a sequence whose length is the fixed maximum length. This is my personal
favorite, since it uses the FinalUnused that is already in the grammar.
E.g., suppose the length of the longest
variant is 258 bytes.
<sequence dfdl:lengthKind="explicit"
dfdl:length="258" dfdl:lengthUnits="bytes" dfdl:applies="hereOnly">
<choice>
.....
</choice>
</sequence>
The only thing I don't like about this
is I don't have a way to express the length other than to hard-code the
constant 258, but since tooling would typically put this in based on Cobol
descriptors or other information I don't mind so much.
...mikeb
Mike Beckerle
STSM, Architect, Scalable Computing
IBM Software Group
Information Platform and Solutions
Westborough, MA 01581
direct: voice and FAX 508-599-7148
assistant: Pam Riordan
priordan@us.ibm.com
508-599-7046
| Steve Hanson/UK/IBM@IBMGB
11/16/2007 11:24 AM
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To
| Mike Beckerle/Worcester/IBM
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cc
| dfdl-wg@ogf.org
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Subject
| Re: [DFDL-WG] Grammar as adapted to
infosetLink |
|
Hi Mike
One extra thought post-call, caused
by thinking about the FinalUnused part of a sequence.
Some fixed length choices have a rule that each branch of the choice must
be of equal length. This results in unused bytes for branches shorter than
the maximum. In a bitstream instance, a user will see these bytes.
Perhaps the grammar should acknowledge their existence, even if there are
no DFDL properties to express the bytes (like FinalUnused)?
Regards, Steve
Steve Hanson
WebSphere Message Brokers
Hursley, UK
Internet: smh@uk.ibm.com
Phone (+44)/(0) 1962-815848
Mike Beckerle <beckerle@us.ibm.com>
Sent by: dfdl-wg-bounces@ogf.org
10/11/2007 00:16
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To
| dfdl-wg@ogf.org
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cc
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Subject
| [DFDL-WG] Grammar as adapted to infoset |
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I took a crack at this. I ripped it out of the main document for faster
review/turnaround.
I think this matches the latest infoset email diagram.
Mike Beckerle
STSM, Architect, Scalable Computing
IBM Software Group
Information Platform and Solutions
Westborough, MA 01581
direct: voice and FAX 508-599-7148
assistant: Pam Riordan
priordan@us.ibm.com
508-599-7046
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