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

Wed Sep 3 08:16:08 EDT 2014

Closed.  After discussion, settled on an xs:long argument being a 1 based 
count up the parent axis. It is a processing error if the argument reaches 
beyond the root. It is a schema definition error if the argument is <= 0. 
Erratum 2.167 created. To be included in draft r23.

Regards

Steve Hanson
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848

From:   Mike Beckerle <mbeckerle.dfdl at gmail.com>
To:     "dfdl-wg at ogf.org" <dfdl-wg at ogf.org>, 
Date:   02/09/2014 15:21
Subject:        Re: [DFDL-WG] Action 269: clarification on 
dfdl:occursIndex()      function
Sent by:        dfdl-wg-bounces at ogf.org

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 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
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