[DFDL-WG] is this legal
Steve Hanson
smh at uk.ibm.com
Fri Mar 1 05:50:39 EST 2013
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 at uk.ibm.com
tel:+44-1962-815848
From: Tim Kimber/UK/IBM at IBMGB
To: dfdl-wg at ogf.org,
Date: 01/03/2013 10:15
Subject: Re: [DFDL-WG] is this legal
Sent by: dfdl-wg-bounces at 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 at uk.ibm.com
Tel. 01962-816742
Internal tel. 37246742
From: Steve Hanson/UK/IBM at IBMGB
To: Suman Kalia <kalia at ca.ibm.com>,
Cc: dfdl-wg at ogf.org, dfdl-wg-bounces at ogf.org
Date: 01/03/2013 08:56
Subject: Re: [DFDL-WG] is this legal
Sent by: dfdl-wg-bounces at 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 at uk.ibm.com
tel:+44-1962-815848
From: Suman Kalia <kalia at ca.ibm.com>
To: Mike Beckerle <mbeckerle.dfdl at gmail.com>,
Cc: dfdl-wg at ogf.org, dfdl-wg-bounces at ogf.org
Date: 01/03/2013 01:11
Subject: Re: [DFDL-WG] is this legal
Sent by: dfdl-wg-bounces at 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 at ca.ibm.com
For info on Message broker
http://www.ibm.com/developerworks/websphere/zones/businessintegration/wmb.html
From: Mike Beckerle <mbeckerle.dfdl at gmail.com>
To: dfdl-wg at ogf.org,
Date: 02/28/2013 07:44 PM
Subject: [DFDL-WG] is this legal
Sent by: dfdl-wg-bounces at 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
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