[DFDL-WG] Representing multiple spaces

[Steve Hanson]

Mike, you can hit XSD UPA problems whether or not an element appears 
directly in a sequence or within a contained sequence. UPA is about 
unambiguously interpreting what you get in the data, so sequences are 
invisible to the rules. The technique(s) you suggest below will work ok 
only if all the 'data' elements do not have minOccurs '0', which allows 
XSD to unambiguously match an instance of the 'spaces' element.

Note to James - IBM DFDL does not yet support dfdl:hiddenGroupRef.

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:   Mike Beckerle <mbeckerle.dfdl at gmail.com>
To:     "Garriss Jr., James P." <jgarriss at mitre.org>, 
Cc:     "dfdl-wg at ogf.org" <dfdl-wg at ogf.org>
Date:   01/03/2013 00:56
Subject:        Re: [DFDL-WG] Representing multiple spaces
Sent by:        dfdl-wg-bounces at ogf.org



%WSP+; is one or more whitespaces. that might be what you want.

The only way to do one or more %SP; (I think you meant %SP*; not %ES*; - 
ES is empty string) only is like this

dfdl:terminator="%SP; %SP;%SP; %SP;%SP;%SP; ..."
i.e, a whitepace separated list of one space, two spaces, three spaces, 
etc. up to as high as you would like to go.

If that just won't cut it, then you have to go to something i call 
modeling syntax as data:

You create a group

<group name="spaces">
   <sequence>
     <xs:element name="spaces" type="xs:string" dfdl:lengthKind="pattern" 
dfdl:lengthPattern="\s*"/>
  </sequence>
</group>

This spaces group is a model for something that is just a syntactic 
feature of your data.

Then you keep the group out of your logical infoset by using a hidden 
group ref like so

<sequence>
  <element name="beforeSpaces" type="xs:string" dfdl:terminator="%SP;"/> 
  <sequence dfdl:hiddenGroupRef="tns:spaces"/>
  <element name="afterSpaces" type="xs:string"dfdl:terminator="%SP;"/>
</sequence>

Here's what I'm not sure of....

In XSD, it would be ok to have multiple groups like this between elements, 
because the elements aren't named "spaces", so the various instances of 
the "spaces" element can't be confused. (There is no UPA problem.)

In DFDL, I'm not sure if we allow this:

<sequence dfdl:sequenceKind="ordered">
    <element name="foo" .../>
    <element name="spaces" .../>
    <element name="bar" .../>
    <element name="spaces".../>
     ....
</sequence>

I.e., more than one child element named "spaces" in the same sequence, but 
it's not an array using minOccurs/maxOccurs and dfdl:occursCountKind, etc.

XML Schema would not have a problem with this, so long as those elements 
are all required. (minOccurs >= 1). 

I've sent a separate email to the dfdl-wg to see what others' opinions are 
on this.



On Thu, Feb 28, 2013 at 3:03 PM, Garriss Jr., James P. <jgarriss at mitre.org
> wrote:
Suppose I have a terminator that can be multiple spaces, whether 0 spaces, 
1 space, 2 spaces, or more spaces.  No other types of whitespace allowed, 
just spaces.
 
Because there’s this entity:  %WSP*;
 
I assumed there would also be this entity:  %ES*;
 
But there’s not.  Why not?  How would I represent this terminator?

TIA

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