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

[Mike Beckerle]

I think we need to add Section 16.1.6, which is titled "When maxOccurs is
Zero". (The other possible place is 16.9, but I think that is very far from
where the information is needed.) This is where the table goes specifying
the maxOccurs 0 behavior.

A forward reference to this section should be added in section 14.2.2 in
the paragraphs about 'fixed', 'implicit', and 'expression'.

A forward reference to this section should also be added in section 16.1.1,
16.1.2, and 16.1.4, which are the sections about fixed, implicit, and
expression.

Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology |
www.tresys.com
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On Tue, Nov 18, 2014 at 6:39 AM, Steve Hanson <smh at uk.ibm.com> wrote:

> We still need words to capture what is in the two tables though.  The spec
> today does not say what the parser or unparser does when asked to process
> zero occurrences of an element (whether stipulated by maxOccurs or
> dfdl:occursCount), and that's the behaviour given in the tables and
> accompanying notes.
>
> 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
>
>
>
> From:        Mike Beckerle <mbeckerle.dfdl at gmail.com>
> To:        Steve Hanson/UK/IBM at IBMGB
> Cc:        DFDL-WG <dfdl-wg at ogf.org>
> Date:        17/11/2014 20:02
> Subject:        Re: [DFDL-WG] Action 271: semantic of maxoccurs '0'
> ------------------------------
>
>
>
> 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* <http://www.tresys.com/>
> Please note: Contributions to the DFDL Workgroup's email discussions are
> subject to the *OGF Intellectual Property Policy*
> <http://www.ogf.org/About/abt_policies.php>
>
>
> On Mon, Oct 13, 2014 at 10:39 AM, Steve Hanson <*smh at uk.ibm.com*
> <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* <%2B44-1962-815848>
> 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
>
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