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



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

________________________________
From: Steve Hanson [smh@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@uk.ibm.com<mailto:smh@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@ogf.org,
Cc:        dfdl-wg-bounces@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@uk.ibm.com<mailto:smh@uk.ibm.com>
tel:+44-1962-815848



From:        Tim Kimber/UK/IBM@IBMGB
To:        dfdl-wg@ogf.org,
Date:        28/07/2014 23:51
Subject:        Re: [DFDL-WG] clarification on dfdl:occursIndex() function
Sent by:        dfdl-wg-bounces@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@gmail.com>
To:        "dfdl-wg@ogf.org" <dfdl-wg@ogf.org>
Date:        28/07/2014 23:27
Subject:        [DFDL-WG] clarification on dfdl:occursIndex() function
Sent by:        dfdl-wg-bounces@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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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