[DFDL-WG] Optional Initiator and Terminator?

[Steve Hanson]

If you parse and then serialize, are you bothered whether the  { } are 
preserved from input to output? 

Regards

Steve Hanson
Architect, Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848



From:   "Garriss Jr., James P." <jgarriss at mitre.org>
To:     "dfdl-wg at ogf.org" <dfdl-wg at ogf.org>, 
Date:   12/03/2013 12:33
Subject:        Re: [DFDL-WG] Optional Initiator and Terminator?
Sent by:        dfdl-wg-bounces at ogf.org



> I suggested the use of an escape scheme to handle this
 
Yes, you did.  :-)  You have correctly perceived the original intentions 
of these initiators/discriminators; however, in practice, the escape 
characters never appear, so they are genuinely superfluous, thus I don’t 
think the escape scheme approach is best.
 
> The 'sequence' is more flexible as it gives you the possibility of 
hiding the brackets from the infoset using dfdl:hiddenGroupRef.
 
This is helpful, and I’ll try it this way. 
 
Thank you!
 
From: Steve Hanson [mailto:smh at uk.ibm.com] 
Sent: Monday, March 11, 2013 5:42 AM
To: Cranford, Jonathan W.
Cc: dfdl-wg at ogf.org; dfdl-wg-bounces at ogf.org; Garriss Jr., James P.
Subject: Re: [DFDL-WG] Optional Initiator and Terminator?
 
In an earlier email exchange on this subject, I suggested the use of an 
escape scheme to handle this, assuming that the { } are either both absent 
or both present, using properties escapeKind 'escapeBlock', 
escapeBlockStart '{', escapeBlockEnd '}'. The disadvantage of this 
approach is when serializing - you need to set property 
generateEscapeBlock to 'always' or 'whenNeeded' - there is no setting for 
'remember what it was when parsed'. That may or may not be a requirement 
here. 

If an escape scheme is not appropriate, then whether the 'choice' or 
'sequence with optionality' approach is best is really up to you. It all 
depends on how you want to manipulate the infoset subsequently. The 
'sequence' is more flexible as it gives you the possibility of hiding the 
brackets from the infoset using dfdl:hiddenGroupRef. 

To Jonathan's point, if the { } are either both absent or both present. 
you can place a dfdl:assert on the sequence which throws an error if the 
brackets are unbalanced. 

Regards

Steve Hanson
Architect, Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848 



From:        "Cranford, Jonathan W." <jcranford at mitre.org> 
To:        "Garriss Jr., James P." <jgarriss at mitre.org>, "dfdl-wg at ogf.org" 
<dfdl-wg at ogf.org>, 
Date:        08/03/2013 21:29 
Subject:        Re: [DFDL-WG] Optional Initiator and Terminator? 
Sent by:        dfdl-wg-bounces at ogf.org 




I don’t know the answer to the DFDL portion of your question, but I can 
say your two workarounds aren’t equivalent. The latter will accept an 
initiator with no terminator, and vice versa (e.g., “{ data” and “data }”, 
while the former will not. 
  
HTH, 
  
Jonathan 
  
  
From: dfdl-wg-bounces at ogf.org [mailto:dfdl-wg-bounces at ogf.org] On Behalf 
Of Garriss Jr., James P.
Sent: Friday, March 08, 2013 12:42 PM
To: dfdl-wg at ogf.org
Subject: [DFDL-WG] Optional Initiator and Terminator? 
  
Is there a way to specify that an initiator/terminator pair is optional? 
  
IOW, these are both valid: 
  
  { data } 
  data 
  
If not, which of these workarounds is better (and why)? 
  
Choice 
    DataWithInitiatorAndTeminator 
   DataWithoutInitiatorAndTeminator 
  
Or 
  
Sequence 
  OptionalInitiator (0 to 1) 
  Data 
  OptionalTerminator (0 to 1) 
  
These seem the same to me, but maybe there’s a reason why one is better.--
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