[DFDL-WG] Action 271: semantic of maxoccurs '0'

[Mike Beckerle]

I looked through the Spec at each use of the word maxOccurs.

I saw nowhere that had to be modified if we stipulate that maxOccurs can be
zero.

Hence, I think the only thing we need to do is (1) explicitly state
maxOccurs can be zero, and I suggest we also provide a suggested use case.
I think the use case would be to accept a prior version of a DFDL-described
data format, but have validation fail for elements that are not supposed to
be present anymore in a revised version of that schema.

I believe section 5.2.1 is the right place for this stipulation. The use
case can go in a footnote perhaps.


Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology |
www.tresys.com
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On Mon, Oct 13, 2014 at 10:39 AM, Steve Hanson <smh at uk.ibm.com> wrote:

>   *271*
> *Use of maxOccurs '0' (All)*
> 2/9: Legal in XSDL and DFDL. One use case in XSDL is when deriving a
> complex type by restriction, where it is used to indicate that an element
> in the base type must not appear. Another use case could be if a schema
> undergoes a version revision that removes elements; perhaps clearer if the
> removed element gets maxOccurs '0' rather than omitting it. Steve has seen
> an instance of its use in a DFDL schema.
> So if DFDL continues to support it, need to document the behaviour for the
> various occursCountKinds and what happens to separator. Also behaviour of
> occursCount expression that returns 0. Proposal needed.
> ...
> 23/9: No progress
>
> IBM has discussed this internally and has the following proposal. Infoset
> refers to the augmented infoset.
>
>  *OCK*
> *maxOccurs '0'*
>  *Parsing* *Unparsing* fixed No occurrences looked for in the data (1) No
> occurrences looked for in the infoset or written (2) implicit No
> occurrences looked for in the data (1) No occurrences looked for in the
> infoset or written (2) expression occursCount occurrences expected. If
> any are found it is a validation error. Any number of occurrences
> expected in the infoset and written. If any are found it is a validation
> error. parsed Any number of occurrences expected in the data. If any are
> found it is a validation error. Any number of occurrences expected in the
> infoset and written. If any are found it is a validation error. stopValue Any
> number of occurrences expected in the data. If any are found it is a
> validation error. Any number of occurrences expected in the infoset and
> written. If any are found it is a validation error.
>
>  *OCK* *Parsing and occursCount '0'* *Unparsing and no occurrences in
> infoset* expression No occurrences looked for in the data. (1) No
> occurrences written. (2)
>
>
> *Notes*
>
> (1) If sequence has a separator, no separator is looked for in the data
> when parsing.
>
> (2) If sequence has a separator, no separator is output when unparsing.
>
>
> Regards
>
> Steve Hanson
> Architect, *IBM DFDL*
> <http://www.ibm.com/developerworks/library/se-dfdl/index.html>
> Co-Chair, *OGF DFDL Working Group* <http://www.ogf.org/dfdl/>
> IBM SWG, Hursley, UK
> *smh at uk.ibm.com* <smh at uk.ibm.com>
> tel:+44-1962-815848
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> IBM United Kingdom Limited - Registered in England and Wales with number
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>
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