[DFDL-WG] do we allow indexing of non-array, non-optional

[Mike Beckerle]

We need to create an action item for this topic:

In minutes of 2014-10-28 we took the position that 'x[1]' is allowed on
scalars, and implementations can warn.

However,....

I just spotted this language in the latest DFDL spec, section 2.6

•    Expression Errors

   - Indexing of non-array non-optional element

Example: x[1] when x is declared and has both minOccurs="1" and
maxOccurs="1" explicitly, or by not stating either or both of them.

Oops...

So it appears we already took a position on whether x[1] is allowed for
scalars. It's not. It's a schema definition error.

However, this wording suggests x[1] allowed for optional elements - and
this is redundant as just 'x' would be sufficient. To me that's ok, as when
dfdl:occursCountKind='parsed' we don't use maxOccurs anyway, so any
non-scalar is in fact treated as an array.

The issue here of course is not about the constant expression '1', but
e.g., 'x[$myVar]', when $myVar might or might not have value 1 at runtime.
In general you cannot tell.

If we believe there should be additional mention of this behavior later in
the spec in section 23, then that could be added, but I don't think we
should change this aspect of DFDL. I believe it actually makes
implementations harder if one blurs the lines between scalars and
arrays/optionals. Right now they are reasonably cleanly separated.

...mikeb



Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology |
www.tresys.com
Please note: Contributions to the DFDL Workgroup's email discussions are
subject to the OGF Intellectual Property Policy
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On Tue, Oct 28, 2014 at 2:06 PM, Steve Hanson <smh at uk.ibm.com> wrote:

> Agreed on call not to add any extra restriction but a DFDL implementation
> is free to issue a warning if it detects such usage.
>
> 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:        Tim Kimber/UK/IBM at IBMGB
> To:        dfdl-wg at ogf.org
> Date:        16/10/2014 05:58
> Subject:        Re: [DFDL-WG] do we allow indexing of non-array,
> non-optional
> Sent by:        dfdl-wg-bounces at ogf.org
> ------------------------------
>
>
>
> I don't think we should depart from the standard XPath rules any more than
> is necessary. Sometimes an XPath author will put [1] after every scalar
> element as a matter of habit, because it makes the execution of the
> expression faster ( in some XPath processors ).
>
> regards,
>
> Tim Kimber,
> Technical Lead for IBM Integration Bus Healthcare Pack
> Hursley, UK
> Internet:  kimbert at uk.ibm.com
> Tel. 01962-816742
> Internal tel. 37246742
>
>
>
>
> From:        Mike Beckerle <mbeckerle.dfdl at gmail.com>
> To:        "dfdl-wg at ogf.org" <dfdl-wg at ogf.org>
> Date:        15/10/2014 22:05
> Subject:        [DFDL-WG] do we allow indexing of non-array, non-optional
> Sent by:        dfdl-wg-bounces at ogf.org
>  ------------------------------
>
>
>
> I don't recall whether we decided this matter or not. I would search for
> it myself, but I tried and failed to find anything. This is a hard topic to
> do searching on... no good keywords.
>
> If element 'e' has maxOccurs = 1, minOccurs = 1 (or neither are
> mentioned), is e[1] a valid expression? what about e[../some/pathExp/here]?
>
> If element 'e' has minOccurs= 0 maxOccurs = 1, is e[1] a valid expression,
> or do you access an optional element just by ../e ?
>
>
> 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>
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