Re: [DFDL-WG] Fw: * DFDL Errata* Clarification: Limitations on use of endOfParent

23 Jan 2012

      Only question I have is on "endOfParent" not being allowed on root element.

If you have a DFDL implementation processing message buffers, and the root
element's content ends at the end of the buffer/end-of-data, how do we
express that?

I expected that to be end-of-parent, the notion being that there's an
implicit parent for all content, which has an end which is the true
end-of-data.

...mikeb

On Mon, Jan 23, 2012 at 6:19 AM, Steve Hanson  wrote:
...
----- Forwarded by Steve Hanson/UK/IBM on 23/01/2012 11:16 -----
From:        Steve Hanson/UK/IBM
To:        Mike Beckerle , Tim Kimber/UK/IBM
Date:        18/01/2012 16:26
Subject:        * DFDL Errata* Clarification:  Limitations on use of
endOfParent
------------------------------
As agreed on WG extra call on 18th Jan.
Will be raised as a separate issue on next DFDL WG call.
Constraints on element lengthKind 'endOfParent'...
- element maxOccurs = 1
- no terminator on element
- if element is in a sequence
    - separatorPolicy of  sequence must not be 'postFix'
    - sequenceKind of sequence must be 'ordered'
    - no floating elements in the sequence
    - must be the 'last' in the sequence statically **
- if element is in a choice it is always 'last' statically **
- parent element lengthKind must not be 'implicit' or 'delimited'
- if element is complex then all possible 'last' elements ** must also be
'endOfParent'
- not sensitive to any in-scope markup
- not allowed on root element
** Need a concise description of walking the content of a complex element
and building the list of 'last elements'. Involves factoring out local
sequences and coping with choices.
Regards
Steve Hanson
Architect, Data Format Description Language (DFDL)
Co-Chair, *OGF DFDL Working Group* http://www.ogf.org/dfdl/
IBM SWG, Hursley, UK*
**smh@uk.ibm.com* 
tel:+44-1962-815848
From:        Steve Hanson/UK/IBM
To:        Mike Beckerle 
Cc:        Tim Kimber/UK/IBM@IBMGB
Date:        08/11/2011 18:22
Subject:        Re: Coping with Character code U+0000 - and how to
end-of-parent in an array
------------------------------
Hi Mike
For the record, I knew we said something about U+0000 - it's in section
5...
*        String – In DFDL a string can contain any character codes. None
are reserved. (Including the character with character code U+0000, which is
not permitted in XML documents.)*
After discussion with Sandy Gao, this is what we wrote in the DFDL to XDM
mapping document:
*Note: SimpleElement [datavalue] values may contain characters that are
illegal in XML, for example, DFDL strings can contain the character code 0
(zero) within them, but XML does not allow this character code in any XML
content even if it is represented as a character entity. Nevertheless, a
DFDL described string is mapped to an XDM string data value.*
and later for the actual mapping to XDM:
*SimpleElement:* If the value of *[datavalue]* is special value *“nil”*,
then the empty string, otherwise the value of *[datavalue]* converted to
its canonical lexical representation.
On to your examples (and assuming separatorPosition is 'infix')...
You are right about the first (endOfParent) example being odd. This
example would work fine if the lengthKind was 'delimited'. Remember that
the 'explicit' length of the parent element creates a box which scopes the
delimited behaviour.
The second (delimited) works fine.
endOfParent and delimited behave almost identically most of the time. When
the element is an array, this looks to be one of the differences. I am
thinking that endOfParent should not be allowed when maxOccurs > 1.
Regards
Steve Hanson
Architect, Data Format Description Language (DFDL)
Co-Chair, *OGF DFDL Working Group* http://www.ogf.org/dfdl/
IBM SWG, Hursley, UK*
**smh@uk.ibm.com* 
tel:+44-1962-815848
From: Mike Beckerle  To: Steve
Hanson/UK/IBM@IBMGB, Tim Kimber/UK/IBM@IBMGB Date: 08/11/2011 17:02
Subject: Coping with Character code U+0000 - and how to end-of-parent in
an array
------------------------------
We have this incompatiability with XML infoset around U+0000 aka NUL.
However, one can model data containing character code U+0000 in the
content as an array of strings with NUL termination. That is, we split the
string on the NUL characters so as to avoid putting them in the infoset.
So I tried to do this and ran into issues. E.g., if data contains a string
of length 80, but inside it the character code 0 can appear, then this
could be modeled as:
<element name="stringsWithNul" dfdl:lengthKind="fixed" dfdl:length="80">
  <sequence dfdl:separator="%x0000;">
  <element name="substring" type="string" maxOccurs="80"
dfdl:lengthKind="endOfParent" />  <!-- ????  -->
  </sequence>
</element>
Problem: is that use of endOfParent length kind right? It's the last thing
in the group, but the same element decl also describes the prior elements.
If there are no NULs in the string, then endOfParent is exactly what you
want. There will be only one substring, it will have all 80 characters. But
if there are NULs in the middle, then you want the earlier array elements
to be delimited by the sequence's separators, and only the last element to
be delimited by endOfParent.
This semantics where the parent is providing the constraints on length,
but sometimes its separator, just for the last thing it's endOfParent, is
not something we can express I believe.
I was actually even unclear on this one: If the data 'string' has a
terminator of ! then perhaps:
<element name="stringsWithNul" dfdl:lengthKind="delimited"
dfdl:terminator="!">
  <sequence dfdl:separator="%x0000;">
  <element name="substring" type="string" maxOccurs="unbounded"
dfdl:lengthKind="delimited"/> <!-- delimited entirely by
ancestor/enclosing-specified delimiters. -->
  </sequence>
</element>
Is the array element delimited? Is that the right length kind for this
situation?
Thanks for comments
...mikeb
...mikeb
------------------------------
*
*
*Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number
741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU
*
------------------------------
*
*
*Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number
741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU
*
------------------------------
*
*
*Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number
741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU
*
--
 dfdl-wg mailing list
 dfdl-wg@ogf.org
 https://www.ogf.org/mailman/listinfo/dfdl-wg
-- 
Mike Beckerle | OGF DFDL WG Co-Chair
Tel:  781-330-0412