What does 'current element declaration' mean? Typically I would want to use dfdl:occursCount() from an element that is not an array, to get the count of an element that is. And if used when parsing from within an array, it can only give the current count which might change as parsing proceeds.

Regards

Steve Hanson
Architect, Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh@uk.ibm.com
tel:+44-1962-815848

From: Tim Kimber/UK/IBM@IBMGB
To: dfdl-wg@ogf.org,
Date: 01/03/2013 10:15
Subject: Re: [DFDL-WG] is this legal
Sent by: dfdl-wg-bounces@ogf.org

Interesting thread.

I agree that the xsd is a valid DFDL xsd. No problem with same-named siblings as long as they obey XML Schema rules.

Steve has raised a related question : what is dfdl:occursCount() for? How does it differ from XPath's fn:count(). We could define it like this:
- fn:count() returns the count of all occurrences from all element declarations.
- dfdl:occursCount() returns the number of occurrences of the current DFDL array. That means the current element declaration, excluding occurrences from same-named previousi siblings.

Why is this useful? I don't know. But I do know that a DFDL array involves exactly one element declaration, whereas fn:count() can involve two or more element declarations. Furthermore, the DFDL properties ( especially dfdl:occursCountKind ) might be different on the two same-named element declarations, so it is possible that the author of the DFDL schema might want to treat them differently.

It may sound unlikely that two element declarations will have the same name and different DFDL array properties - but I reckon I could invent some plausible scenarios where it could happen.

regards,

Tim Kimber, DFDL Team,
Hursley, UK
Internet: kimbert@uk.ibm.com
Tel. 01962-816742
Internal tel. 37246742

From: Steve Hanson/UK/IBM@IBMGB
To: Suman Kalia <kalia@ca.ibm.com>,
Cc: dfdl-wg@ogf.org, dfdl-wg-bounces@ogf.org
Date: 01/03/2013 08:56
Subject: Re: [DFDL-WG] is this legal
Sent by: dfdl-wg-bounces@ogf.org

Additionally UPA rules apply. Your example is fine as long as first "foo" and "bar" are not minOccurs '0'.

Using your example, in standard XPath the path expression "foo" would return a sequence of length 2.
A more interesting example is:

<sequence>
<element name="foo" type="int" dfdl:lengthKind="explicit" dfdl:length="1"/ minOccurs="2" maxOccurs="2">
<element name="bar" type="int" dfdl:lengthKind="explicit" dfdl:length="1" minOccurs="0"/>
<element name="foo" type="int" dfdl:lengthKind="explicit" dfdl:length="1"/>
</sequence>

In standard XPath the path expression would now return a sequence of length 3, as it would just lift the 3 occurrences from the infoset. Note they could all be adjacent if "bar" was not in the data.

Given the examples, I don't see how a DFDL path expression can distinguish between the different occurrences of elements with the same name. There is no way in XPath to ask for a count of the number of element occurrences that match a specific element declaration, because there is no way in the language to identify such an element.

The DFDL spec in section 23 says "DFDL expressions never return node-sequences having more than one node. DFDL expressions either return a simple value, a node sequence containing exactly one node/value, or an empty node sequence." and "The result of evaluating the expression must be a single atomic value of the type expected by the context, and it is a schema definition error otherwise. Some XPath expressions naturally return a sequence of values, and in this case it is also schema definition error if an expression returns a sequence containing more than one item". That talks about what is ultimately returned by a DFDL expression. Later it says "(Note that DFDL v1.0 does not support sequences of length > 1.)". And says "DFDL implementations may use off-the-shelf XPath 2.0 processors, but will need to pre-process DFDL expressions to ensure that the behaviour matches the DFDL specification: Wrap path locations in a call to fn:exactly-one() except when the path location occurs within certain functions which operate on arrays". We also said on a recent WG call that dfdl:occursCount() is allowed on non-arrays.

If the real requirement here is that a DFDL expression should not return a sequence > length 1, then is there a problem with allowing intermediate steps to return sequences > length 1 as long as the final result is not > 1 ? Then, couldn't we drop dfdl:occursCount() and just use fn:count() ? Are we just making things hard for implementers?

Regards

Steve Hanson
Architect, Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh@uk.ibm.com
tel:+44-1962-815848

From: Suman Kalia <kalia@ca.ibm.com>
To: Mike Beckerle <mbeckerle.dfdl@gmail.com>,
Cc: dfdl-wg@ogf.org, dfdl-wg-bounces@ogf.org
Date: 01/03/2013 01:11
Subject: Re: [DFDL-WG] is this legal
Sent by: dfdl-wg-bounces@ogf.org

This is certainly allowed in XML schema.. In the sequence you can have multiple elements with same name as long as their type is identical which is the case in your example. I think from XPath perspective, it would be treated like array and if true dldl:occursCount should return 2. .

Suman Kalia
IBM Canada Lab
WMB Toolkit Architect and Development Lead
Tel: 905-413-3923 T/L 313-3923
Email: kalia@ca.ibm.com

For info on Message broker
http://www.ibm.com/developerworks/websphere/zones/businessintegration/wmb.html

From: Mike Beckerle <mbeckerle.dfdl@gmail.com>
To: dfdl-wg@ogf.org,
Date: 02/28/2013 07:44 PM
Subject: [DFDL-WG] is this legal
Sent by: dfdl-wg-bounces@ogf.org

I can't find clarity on this:

<sequence>
<element name="foo" type="int" dfdl:lengthKind="explicit" dfdl:length="1"/>
<element name="bar" type="int" dfdl:lengthKind="explicit" dfdl:length="1"/>
<element name="foo" type="int" dfdl:lengthKind="explicit" dfdl:length="1"/>
<element name="bar" type="int" dfdl:lengthKind="explicit" dfdl:length="1"/>
</sequence>

Is this allowed?

If so, then the XPaths for accessing the 2nd foo would be foo[2], and the path "foo" would be ambiguous or
could be treated as identifying an array. In which case one could do an expression dfdl:occursCount("foo") and get back 2 ??

Or am I completely missing the boat here?

--
Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | www.tresys.com-- dfdl-wg mailing list dfdl-wg@ogf.org
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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-- dfdl-wg mailing list dfdl-wg@ogf.org https://www.ogf.org/mailman/listinfo/dfdl-wg

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