[DFDL-WG] Fw: DFDL array prefix

[Mike Beckerle]

This is where Suman and I left it on the array prefix issue.

The problem is where do you stop with creating special "occurs" versions. 
You can in principle have an "occurs" variant of almost every property.

...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


----- Forwarded by Mike Beckerle/Worcester/IBM on 11/20/2007 10:02 AM 
-----

Suman Kalia/Toronto/IBM at IBMCA 
11/16/2007 11:53 AM

To
Mike Beckerle/Worcester/IBM at IBMUS
cc

Subject
Fw: DFDL array prefix





Mike - The proposed grammar productions seem correct to me..

I see your view point and your concern for bifurcation of properties and I 
do agree that it introduces level of redundancy. I guess the choice boils 
down to having extra level of redundancy (dummy sequence) in the logical 
model or having redundancy in DFDL properties and each alternative can be 
justified and supported with good arguments. From consumability 
perspective having clean and less/no extra level of redundancy in the 
logical model is preferred because  it would be at the user face all the 
time while the DFDL properties pertaining to occurrences will be rare and 
only for specific use cases.  From pure DFDL spec perspective, having no 
redundancy in DFDL properties is desirable.

May be we can go with the conservative approach as  you mentioned  ie not 
add the extra production in the grammar for Array for now but add an 
appendix in the document listing the alternative for overcoming redundancy 
in the logical model and how the revised grammar would look like. We can 
get more feedback when the document is reviewed by IBMers (architects, 
implementers, UCD) and folks in the standards community. 


Suman Kalia
IBM Toronto Lab
WebSphere Business Integration Application Connectivity Tools 
Tel : 905-413-3923  T/L  969-3923
Fax : 905-413-4850 T/L  969-4850
Internet ID : kalia at ca.ibm.com
----- Forwarded by Suman Kalia/Toronto/IBM on 11/16/2007 10:34 AM -----

Mike Beckerle/Worcester/IBM at IBMUS 
11/16/2007 10:17 AM

To
Suman Kalia/Toronto/IBM at IBMCA
cc

Subject
DFDL array prefix






Here's the proposal I think:

Array = ArrayPrefix ArrayContent
ArrayContent = [ Element [ OccursSeparator Element ]*  [ OccursSeparator 
StopValue] ]
StopValue = SimpleElement

I'd suggest the keyword occursLeadingSkipBytes is the property which 
controls the ArrayPrefix content. 

My argument against this is a slippery-slope argument.  This starts us 
down the path of having a bifurcation of many properties into an occurs 
and non-occurs flavor. E.g., once you add the above, then by analogy why 
not have these additional keywords which apply to the array as a whole, 
not the elements of it:

occursAlignment
occursAlignmentUnits
occursInitiator
occursTerminator
occursLength
occursLengthKind
occursLengthUnits

All of this is avoided by simply requiring an extra sequence to provide 
these same format characteristics using the ordinary non-occurs keywords, 
and that's very preferable to me to this proliferation of occurs and 
non-occurs variants. 


...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

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