[DFDL-WG] Grammar as adapted to infoset

[Mike Beckerle]

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 at us.ibm.com 
                  508-599-7046





Steve Hanson/UK/IBM at IBMGB
11/16/2007 11:24 AM

To
Mike Beckerle/Worcester/IBM
cc
dfdl-wg at ogf.org
Subject
Re: [DFDL-WG] Grammar as adapted to infoset





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 at uk.ibm.com
Phone (+44)/(0) 1962-815848



Mike Beckerle <beckerle at us.ibm.com> 
Sent by: dfdl-wg-bounces at ogf.org
10/11/2007 00:16

To
dfdl-wg at ogf.org
cc

Subject
[DFDL-WG] Grammar as adapted to infoset







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 at us.ibm.com 
                 508-599-7046
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