[DFDL-WG] Action 269: clarification on dfdl:occursIndex() function

Tue Sep 2 10:20:55 EDT 2014

I am currently implementing functionality in the area where
dfdl:occursIndex( path ) will be in the Daffodil implementation.

It doesn't look very hard to put in a specific argument that is restricted
to be upward only and which identifies exactly which array.

This function is a special case in any DFDL runtime no matter what, and
will require a fair bit of test attention for any implementation so making
it simpler by allowing only the innermost array to be examined isn't saving
a lot of work really.

Question: is a crazy path like ../foo/../../bar/.././.. (which just so
happens to be equivalent to ../../..), a schema definition error?

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
<http://www.ogf.org/About/abt_policies.php>

On Tue, Sep 2, 2014 at 9:28 AM, Mike Beckerle <mbeckerle at tresys.com> wrote:

>
> ________________________________
> From: Steve Hanson [smh at uk.ibm.com]
> Sent: Monday, September 01, 2014 11:08 AM
> To: Mike Beckerle
> Subject: Fw: [DFDL-WG] Action 269: clarification on dfdl:occursIndex()
> function
>
> 269
>         dfdl:occursIndex() function (Steve)
> 29/7: Clarify behaviour and decide whether an argument is needed to make
> it context independent. Noted that fn:position() also does not take an
> argument, but it returns position in current sequence and not position in
> array.
> 4/8: With Steve but consensus is that an argument is needed.
> 26/8: Mike to review. If an argument is needed, we should make sure this
> is in next published spec as the function is used in MIL-STD-2045 schemas.
>
> 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<mailto:smh at uk.ibm.com>
> tel:+44-1962-815848
> ----- Forwarded by Steve Hanson/UK/IBM on 01/09/2014 16:03 -----
>
> From:        Steve Hanson/UK/IBM
> To:        dfdl-wg at ogf.org,
> Cc:        dfdl-wg-bounces at ogf.org
> Date:        31/07/2014 10:57
> Subject:        Re: [DFDL-WG] clarification on dfdl:occursIndex() function
>
> ________________________________
>
>
> Note:  The reason why fn:position() takes no argument is because it gives
> position in the current sequence. Which is also why we have a separate DFDL
> specific function dfdl:occursIndex() which is intended for giving position
> in enclosing array. I think we need an argument that targets the specific
> enclosing array.
>
> 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<mailto:smh at uk.ibm.com>
> tel:+44-1962-815848
>
>
>
> From:        Tim Kimber/UK/IBM at IBMGB
> To:        dfdl-wg at ogf.org,
> Date:        28/07/2014 23:51
> Subject:        Re: [DFDL-WG] clarification on dfdl:occursIndex() function
> Sent by:        dfdl-wg-bounces at ogf.org
> ________________________________
>
>
>
> I agree that it is inconvenient for the 'nearest array parent' to be
> inaccessible. However, experience with discriminators makes me fearful of
> any rule that includes the phrase 'nearest enclosing' :-)
> I think at least one other DFDL function allows the target of the function
> to be specified as an argument, but insists that the argument must be in
> the dynamic scope of the element ( i.e. its parent/grandparent etc ). I
> would be much happier with that solution for occursCountIndex().
>
> I can think of a use case where it may be useful to get a consistent
> behaviour for occursCountIndex(). If a DFDL schema is generated from some
> other data format description then the model generation code may want to
> refer to the nth occurrence of something else in the model, where n is the
> occurs index of the current element - regardless of whether this particular
> element is an array.
>
> regards,
>
> Tim Kimber,
>
>
>
>
> From:        Mike Beckerle <mbeckerle.dfdl at gmail.com>
> To:        "dfdl-wg at ogf.org" <dfdl-wg at ogf.org>
> Date:        28/07/2014 23:27
> Subject:        [DFDL-WG] clarification on dfdl:occursIndex() function
> Sent by:        dfdl-wg-bounces at ogf.org
> ________________________________
>
>
>
> This function says it can be called on non-array elements. However, it
> does not say what the result is.
>
> If called when "." is not itself an array element there are only two
> possible behaviors consistent with the fact that it is explicitly allowed
> on non-array elements.
>
> The result has to be either
>
> (a) 1
> (b) the occursIndex of the nearest enclosing array parent, or 1 if there
> is no enclosing array parent.
>
> I claim (a) is fairly pointless. You will just end up having to create
> newVariableInstances to carry the array current index downward into
> expressions.
>
> I cannot think of a use case where one would want to call occursIndex()
> polymorphically, i.e., where you want a number in the case of an array, but
> 1 otherwise.
>
> So (b) is the preferable behavior.
>
>
> 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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> 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
>
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