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January 2006
- 8 participants
- 27 discussions
Hi Folks,
For those coming to the F2F I have the attached information on hotels
and directions.
The Crowne Plaza seems nice and is very close - I have never stayed
there. I did stay at the Courtyard Marriott once, a long time ago and
its fine except it has no bar or restaurant.
Martin
3
2
These are documents 3 and 4 of a set of 3 :).
The documents are:
- bundles - a reusable block of DFDL statements
- Conversions - a proposal for the semantic details as to how
conversions are chosen during the operation of a DFDL parser. These
semantics include a description as to how the conversions can be
extended.
These documents round off the current set of proposals from the
extensibility design team. The team has reasonable consensus on these
documents, with the (relatively trivial) exception of bundles where
there may be some outstanding issues. We believe that with these two
documents there is enough material to support the necessary
extensibility. However, we have not yet worked through enough examples
of round tripping to understand whether that is sufficiently well
covered and we are expecting that all the ideas in these documents will
require refining by the group as a whole.
I would like to discuss these two documents on Wednesday (if possible).
Thanks,
Martin
4
4
Please note: We need to agree a preliminary agenda for the F2F by the
end of the week. Please take a look at the agenda at the end of this
document and send comments/additions to the list. Our face-to-face time
is limited, I am keen to try to direct our attention to strategy and big
picture questions and leave details for the telcons. I propose to devote
some call-time to each agenda item to fine-tune what the outstanding
issues for discussion are.
Present
Geoff Judd
Bob McGrath
Tara Talbott
Martin Westhead
Suman Kalia
Agenda
1. US F2F Logistics
Meeting is set for 1-3 March in Milpitas. Agenda details are required
urgently, for Suman's travel request.
2. Reports from trackers
Final extensibility documents presented.
3. Outstanding issues on hidden elements
Discussion lead to the observations that:
a) putting things into a global complex type appears to be the
only way to avoid any possible name clash issues.
b) We could restrict things to this, or document this as a best
practice.
Suman is in favour of restricting the language in order to avoid this
problem. The issue remains open at this point.
4. Review "Bundles" document
We did not get to this.
5. Review "Conversions" document
We had an initial discussion on the conversions document. There were a
lot of questions about motivations and the extent to which this proposal
would change things. More discussion will be needed to bring the group
to a common understanding of the proposal.
Face-to-face agenda
Conversions/context/hidden elements
Scoping document
Choices and defaults
Actions to lead to a final document set.
3
2
BTW - I can confirm that Avaya would be happy to host the F2F at the
beginning of March, so we should go ahead and plan for that.
Preliminary Agenda
------------------
1. US F2F Logistics
2. Reports from trackers
3. Outstanding issues on hidden elements
4. Review "Bundles" document
5. Review "Conversions" document
Conference call instructions:
Number: 1-800-664-0771
At the automated answering system, press 0 for the operator.
Ask for the "Daffodil working group" call.
Web Conference: https://webconferencing.avaya.com
<https://webconferencing.avaya.com/>
Web Conference Reference: 158672
Security Code : 785343
2
1
RE: [dfdl-wg] RE: Attributes - (was Ambiguous XPaths to hidden elements)
by Westhead, Martin (Martin) 24 Jan '06
by Westhead, Martin (Martin) 24 Jan '06
24 Jan '06
I'm afraid I don't understand. I guess I need to see some real examples.
I hear you saying that including attributes would require significant
extra work. That it would make the language more complicated for the
users and harder to write implementations of. Unfortunately I don't have
enough of an implementation perspective to understand or argue with you.
What I propose is this. Let us finish this discussion of the underlying
semantics; I have more material to present. And then perhaps we can have
this discussion with some examples. From where I am sitting I don't see
attributes introducing all the corner cases you are worried about. If
the generalization is right some of these may simplify.
Cheers,
Martin
>-----Original Message-----
>From: owner-dfdl-wg(a)ggf.org [mailto:owner-dfdl-wg@ggf.org] On Behalf Of
>Steve Hanson
>Sent: Friday, January 20, 2006 1:56 AM
>To: Westhead, Martin (Martin)
>Cc: dfdl-wg(a)ggf.org
>Subject: [dfdl-wg] RE: Attributes - (was Ambiguous XPaths to hidden
>elements)
>
>Regarding attributes, it is not true to say that there is no extra work
to
>do. Once you allow attributes into the equation you have to consider
not
>only Mike's points below but also questions like where you put
>construct-specific annotations for groups of attributes, and how do you
>handle complex type with simple content. Attributes are not a small
delta
>on the XML spec. In the existing IBM model we started with a Schema
centric
>view and allowed all this and it has caused us many problems in the
>implementation. It certainly muddies the waters for non-XML users
starting
>off with the IBM model, most of whom aren't interested in attributes,
to
>the extent that many users are put off from using the model altogether.
I
>think DFDL should be approaching the problem from the "I have some
non-XML
>data let me model it" angle and not "Here is XML Schema let's provide a
way
>of representing all its constructs in non-XML form". I strongly believe
>that to get DFDL adoption going, the 1.0 spec should do the minimum
>possible to permit the modelling of all types of non-XML data. That's a
big
>enough task in itself. Stuff like allowing an easy transformation into
XML
>with attributes or substitution groups can wait for a second release,
if it
>is something that users want. If you make the scope of a DFDL parser
too
>wide, no-one will write one.
>
>Regards, Steve
>
>Steve Hanson
>WebSphere Message Brokers,
>IBM Hursley, England
>Internet: smh(a)uk.ibm.com
>Phone (+44)/(0) 1962-815848
>
>
>
> "Westhead, Martin
> \(Martin\)"
> <westhead(a)avaya.c
To
> om> "Mike Beckerle"
> <beckerle(a)us.ibm.com>
> 19/01/2006 20:59
cc
> <dfdl-wg(a)ggf.org>, "Suman Kalia"
> <kalia(a)ca.ibm.com>,
> <owner-dfdl-wg(a)ggf.org>, Steve
> Hanson/UK/IBM@IBMGB
>
Subject
> RE: Attributes - (was Ambiguous
> XPaths to hidden elements)
>
>
>
>
>
>
>
>
>
>
>Well I wasn't saying that. I was saying that you could do that if
things
>didn't line up.
>
>I suppose I don't feel strongly about the restriction I just don't
really
>see the need.
>
>I have a number of examples of XML which are essentially tables with
lists
>of elements with just attributes. I could imagine it would be easy and
>convenient to populate such a logical model directly using annotations
>without forcing the user to add hidden layers...
>
>Martin
>
>
>From: Mike Beckerle [mailto:beckerle@us.ibm.com]
>Sent: Thursday, January 19, 2006 12:55 PM
>To: Westhead, Martin (Martin)
>Cc: dfdl-wg(a)ggf.org; Suman Kalia; owner-dfdl-wg(a)ggf.org; Steve Hanson
>Subject: RE: Attributes - (was Ambiguous XPaths to hidden elements)
>
>
>I agree with you.
>
>There is one caveat though, you are saying in effect that attributes
are
>only supported via population to/from other elements or attributes
(which
>can be hidden). The bottom layer must be elements only.
>
>With this restriction I am fine with attributes. The vast bulk of the
DFDL
>spec will simply be unconcerned with them.
>
>...mikeb
>
>Mike Beckerle
>STSM, Architect, Scalable Computing
>IBM Software Group
>Information Integration Solutions
>Westborough, MA 01581
>voice and FAX 508-599-7148
>home/mobile office 508-915-4767
>
>
>
>
>
>
> "Westhead, Martin
> \(Martin\)"
> <westhead(a)avaya.com>
>
To
> Mike
Beckerle/Worcester/IBM@IBMUS
> 01/19/2006 03:45 PM
cc
> <dfdl-wg(a)ggf.org>, "Suman Kalia"
> <kalia(a)ca.ibm.com>,
> <owner-dfdl-wg(a)ggf.org>, "Steve
> Hanson" <smh(a)uk.ibm.com>
>
Subject
> RE: Attributes - (was Ambiguous
> XPaths to hidden elements)
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>Perhaps there is a discussion here for later, but with hidden elements
I
>don't think there's much of an issue here.
>
>My take on this is that we are using the XSD to do more than it is
supposed
>to, we are not just using it to describe valid XML we are using it
>constructively to describe how to build an XML instance. We are
>establishing a semantics for how the DFDL parser constructs this XML
>document from the XSD and the data.
>
>Now, it is easy to imagine cases where you have a particular xml model
you
>want to populate which is similar to the data but is perhaps a subset
with
>slightly different ordering. Hidden elements make this easy to handle.
You
>put the stuff that is to be omitted in a hidden element. Stuff that is
out
>of order can be put in hidden elements and then referenced by correctly
>ordered elements for value.
>
>In this framework attributes are just another node for data population.
If
>it happens that you can arrange the XML Schema so that the order in
which
>attributes are laid out in the file corresponds to the ordering of the
>data, well then its no different from elements. If there are
constraints
>that prevent that ordering then you are in a situation just like the
one I
>describe above and you solve it with hidden elements.
>
>So I don't really disagree with your points below it just seems to me
that
>there's nothing much to worry about here. I can't see why we would put
it
>off - there's no extra work to do?
>
>Cheers,
>
>Martin
>
>
>
>
>
>
>From: Mike Beckerle [mailto:beckerle@us.ibm.com]
>Sent: Thursday, January 19, 2006 12:27 PM
>To: Westhead, Martin (Martin)
>Cc: dfdl-wg(a)ggf.org; Suman Kalia; owner-dfdl-wg(a)ggf.org; Steve Hanson
>Subject: Re: Attributes - (was Ambiguous XPaths to hidden elements)
>
>
>Here's some of the issues with attributes:
>
>1) every element can have two kinds of children now, attributes and
>sub-elements. Actual DFDL-described data will typically have just one
kind
>of sub-fields of data, but some want to be mapped to attributes, others
to
>elements. How do you specify how the attributes are separated from the
>elements. Do the attributes have to be first, or last, or can they be
>interleaved with the sub-elements' physical data?
>2) in XSD syntax, if you define a element with both sub-elements and
>attributes, the attributes textually come after the sub-elements. This
>means you may or may not have them in the right order for DFDL
annotation
>to be convenient. E.g., suppose you had 5 children the first 2 you want
to
>be attributes the remaining 3 sub-elements in a sequence. How can you
>annotate this conveniently?
>3)The attributes are always unordered w.r.t. the XSD concept, but the
>sub-elements can be either ordered or un-ordered.
>
>These all seemed like avoidable issues. That is, I'm not saying there
is no
>good solution here, I'm just saying it's probably uninteresting.
>
>One solution to the whole issue is to say that attributes can't be in
the
>bottom-most layer. I.e., you create them by referencing element values
in
>hidden or non-hidden layers. This eliminates all the above problems.It
is
>equivalent to using a stylesheet to create the attributes you want from
>elements-only data. However, by use of the layers you can embed it all
>right into the DFDL schema.
>
>I also believe attributes are to some extent beside the point for DFDL.
>What we needed from XSD is a standardized hierarchical type system that
we
>can hang represetnation properties on. We get that by using the
>elements-only subset of XSD. Attributes are only needed if we broaden
our
>agenda to include "creating the XML I want out of my data", which
layering
>can do.
>
>Mike Beckerle
>STSM, Architect, Scalable Computing
>IBM Software Group
>Information Integration Solutions
>Westborough, MA 01581
>voice and FAX 508-599-7148
>home/mobile office 508-915-4767
>
>
>
>
> "Westhead, Martin
> \(Martin\)"
> <westhead(a)avaya.com>
>
>
> 01/19/2006 03:05 PM
>
To
> Mike
Beckerle/Worcester/IBM@IBMUS
>
cc
> <dfdl-wg(a)ggf.org>, "Suman Kalia"
> <kalia(a)ca.ibm.com>,
> <owner-dfdl-wg(a)ggf.org>, "Steve
> Hanson" <smh(a)uk.ibm.com>
>
Subject
> Attributes - (was Ambiguous
XPaths
> to hidden elements)
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>I think (hope) that with the emerging operational semantics, that there
>will not be any problems putting annotations into attributes and having
>them evaluated just like an element. It is not obvious to me that they
are
>any different.
>
>Martin
>
>
>
>
>
>
>From: Mike Beckerle [mailto:beckerle@us.ibm.com]
>Sent: Thursday, January 19, 2006 12:03 PM
>To: Westhead, Martin (Martin)
>Cc: dfdl-wg(a)ggf.org; Suman Kalia; owner-dfdl-wg(a)ggf.org; Steve Hanson
>Subject: RE: [dfdl-wg] Ambiguous XPaths to hidden elements
>
>
>I think we did not agree formally to this. It was one of those things
where
>we're trying to find something we can cut out with low risk of later
>complications.
>
>Mike Beckerle
>STSM, Architect, Scalable Computing
>IBM Software Group
>Information Integration Solutions
>Westborough, MA 01581
>voice and FAX 508-599-7148
>home/mobile office 508-915-4767
>
>
>
> "Westhead, Martin (Martin)"
> <westhead(a)avaya.com>
> Sent by:
> owner-dfdl-wg(a)ggf.org
>
>
> 01/19/2006 01:59 PM
>
>
>
To
> "Suman Kalia"
> <kalia(a)ca.ibm.com>, "Steve
> Hanson" <smh(a)uk.ibm.com>
>
cc
> Mike
>
Beckerle/Worcester/IBM@IBMUS,
> <dfdl-wg(a)ggf.org>,
> <owner-dfdl-wg(a)ggf.org>
>
Subject
> RE: [dfdl-wg] Ambiguous
XPaths
> to hidden elements
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>Why are we not allowing attributes?
>
>Martin
>
>
>
>
>
>
>
>
>From: owner-dfdl-wg(a)ggf.org [mailto:owner-dfdl-wg@ggf.org] On Behalf Of
>Suman Kalia
>Sent: Thursday, January 19, 2006 10:57 AM
>To: Steve Hanson
>Cc: Mike Beckerle; dfdl-wg(a)ggf.org; owner-dfdl-wg(a)ggf.org
>Subject: Fw: [dfdl-wg] Ambiguous XPaths to hidden elements
>
>
>The main problem will be performance and excessively long validation
times
>and either asking the user to change their schema or model it different
>way. These are all undesirable. Attributes I hope will be supported in
the
>future release . Redefine construct is hardly used in the practical
>applications; at least I haven't come across any customer that uses
this
>construct ..
>
>Suman Kalia
>IBM Toronto Lab
>WebSphere Business Integration Application Connectivity Tools
>Tel : 905-413-3923 T/L 969-3923
>Fax : 905-413-4850
>Internet ID : kalia(a)ca.ibm.com
>----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 01:49 PM -----
>
>
>
> Steve Hanson
> <smh(a)uk.ibm.com>
>
>
> 01/19/2006 01:15 PM
>
>
>
>
>
>
>
>
To
> Suman Kalia/Toronto/IBM@IBMCA
>
cc
> Mike Beckerle
<beckerle(a)us.ibm.com>,
> dfdl-wg(a)ggf.org,
> owner-dfdl-wg(a)ggf.org
>
Subject
> Re: Fw: [dfdl-wg] Ambiguous
XPaths
> to hidden elements
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>We are already putting constraints on user-defined schema, by saying
that
>we don't support redefines and attributes for example. I don't see an
issue
>with further constraints if they make DFDL easier to understand and/or
>easier to create a DFDL parser.
>
>I don't have a problem with saying that an XPath must return a single
>unambiguous node else it is an error.
>I don't have a problem with saying the XPaths can't reference hidden
>elements, and that context must be used instead.
>
>Regards, Steve
>
>Steve Hanson
>WebSphere Message Brokers,
>IBM Hursley, England
>Internet: smh(a)uk.ibm.com
>Phone (+44)/(0) 1962-815848
>
>
>
> Suman Kalia
> <kalia(a)ca.ibm.com
> > To
> Sent by: Mike Beckerle <beckerle(a)us.ibm.com>
> owner-dfdl-wg@ggf cc
> .org dfdl-wg(a)ggf.org,
> owner-dfdl-wg(a)ggf.org
> Subject
> 19/01/2006 18:02 Fw: [dfdl-wg] Ambiguous XPaths to
> hidden elements
>
>
>
>
>
>
>
>
>
>
>
>Well if we go with global complex type approach (which I described
option 1
>in previous append) then it is not issue.. XPATH work and there are no
>conflicts with user defined schemas ..
>
>Suman Kalia
>IBM Toronto Lab
>WebSphere Business Integration Application Connectivity Tools
>Tel : 905-413-3923 T/L 969-3923
>Fax : 905-413-4850
>Internet ID : kalia(a)ca.ibm.com
>----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 12:59 PM -----
>
>Mike
>Beckerle/Worcester/IBM@IBMUS
>
> To
>01/19/2006 12:59 PM Suman
Kalia/Toronto/IBM@IBMCA
> cc
> dfdl-wg(a)ggf.org,
> owner-dfdl-wg(a)ggf.org
> Subject
> Re: Fw: [dfdl-wg] Ambiguous
> XPaths to hidden elementsLink
>
>
>
>
>
>
>
>
>
>
>
>So we have a quandry here:
>
>on one hand we don't want to change the XPath syntax to include a
device
>that would let us be clear that we're navigating a hidden layer
>
>on the other hand we don't want to constrain what can be included so
that
>we wouldn't need such a device.
>
>...mikeb
>
>Mike Beckerle
>STSM, Architect, Scalable Computing
>IBM Software Group
>Information Integration Solutions
>Westborough, MA 01581
>voice and FAX 508-599-7148
>home/mobile office 508-915-4767
>
>
>
>
>Suman Kalia/Toronto/IBM@IBMCA
>
>
>01/19/2006 11:52 AM
To
> Mike
> Beckerle/Worcester/IBM@IBMUS
> cc
> dfdl-wg(a)ggf.org,
> owner-dfdl-wg(a)ggf.org
> Subject
> Fw: [dfdl-wg] Ambiguous
> XPaths to hidden elements
>
>
>
>
>
>
>
>
>
>
>
>As a design point , We should strive not to put limitations on the
user
>defined schemas - it just works out better in the long run.
>
>Note the xsd:groups can be nested and they could be many levels deep
and
>this problem is not restricted to groups included from noTarget
namespace
>, it could be from any namespace. As per schema rules, all local
elements
>defined in groups or complex types belong to noTarget namespace unless
>elementFormDefault is explicitly set to "qualified" at schema level or
on
>the specific element.
>
>Detecting such conflicts could be quite expensive particularly when you
>have very large schemas. Industry standard ACORD messaging schema is a
>good example it is about 1.5 M and it takes awfully long (hours) to
>validate it. Putting additional constraints like this will further
slow
>down validation.
>
>Suman Kalia
>IBM Toronto Lab
>WebSphere Business Integration Application Connectivity Tools
>Tel : 905-413-3923 T/L 969-3923
>Fax : 905-413-4850
>Internet ID : kalia(a)ca.ibm.com
>----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 11:39 AM -----
>
>Mike Beckerle
><beckerle(a)us.ibm.com>
>Sent by: owner-dfdl-wg(a)ggf.org
> To
> "Robert E. McGrath"
>01/19/2006 10:48 AM <mcgrath(a)ncsa.uiuc.edu>
> cc
> dfdl-wg(a)ggf.org,
> owner-dfdl-wg(a)ggf.org
> Subject
> Re: Fw: [dfdl-wg] Ambiguous
> XPaths to hidden elements
>
>
>
>
>
>
>
>
>
>
>
>
>One idea that hasn't been advanced yet is ruling out the problematic
case.
>
>Let me illustrate. Here's the example, modified to have a model group
>reference which can introduce the name conflict:
>
><xs:element name="root">
><xs:complexType>
> <xs:sequence>
> <xs:annotation><xs:appinfo
>source="http://dataformat.org" />
> <hidden>
>
><xs:element name="repeats" type="xs:integer"/>
> </hidden>
> </xs:appinfo></xs:annotation
>>
> <xs:element name="testElement"
>type="xs:integer " minOccurs="0" maxOccurs="unbounded"
> dfdl:repeatCount="../repeats">
>
> <xs:group ref="groupFromOtherSchemaFile"/>
><!-- what if this has an element decl named "repeats"? -->
>
> </xs:complexType>
></xs:element>
>
>So, what hasn't been suggested yet is this: What if we just say DFDL
>doesn't allow this? It's an error which must be detected. This DFDL
schema
>is broken because the path "../repeats" cannot be analyzed along with
the
>DFDL schema to return only a single node.
>
>I beleive name conflicts like this are what namespace management is
for.
>XSD has truly great namespace managment. You can solve the problem that
>way.
>
>Furthermore, when you define a reusable named group like the definer of
the
>"groupFromOtherSchemaFile" above, and you put it in no target
namespace,
>that's the situation where this conflict can arise. Expecting that your
>names are never going to conflict with anything in that case is just
naive.
>It's equivalent to having global variables in a C program module and
>expecting you can never link it to something else that uses the same
names.
>Those name conflicts can occur, and someone has to change the
conflicting
>name. In XSD we can do that by including the group in a schema which
puts
>it into a target namespace so that after that the namespaces can be
used to
>disambiguate.
>
>The approach above is consistent with the path "../repeats" still being
>officialy an "XPath", it just adds the semantic restriction that it
must be
>an XPath that identifies a single node unambiguously, independent of
what
>data is being processed. This is one of these "data independent"
notions
>(what I had previously been calling "static"), as we discussed
yesterday.
>
>...mikeb
>
>
>
>
>"Robert E. McGrath"
><mcgrath(a)ncsa.uiuc.edu>
>Sent by: owner-dfdl-wg(a)ggf.org
> To
> dfdl-wg(a)ggf.org
>01/19/2006 10:00 AM
cc
>
> Subject
> Re: Fw: [dfdl-wg]
> Ambiguous XPaths to hidden
> elements
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>I would want to change XPath only as a last resort. (Any of the
>options is OK by me, assuming we have to mess with the Xpath
>at all.)
>
>Can we deal with this some other way?
>
>Can we document the problematic cases, and suggest best practices that
>will minimize the problem?
>
>On Thursday 19 January 2006 08:45, Suman Kalia wrote:
>> I fully agree with Steve - let's not invent another XPATH like syntax
..
>>
>> Suman Kalia
>> IBM Toronto Lab
>> WebSphere Business Integration Application Connectivity Tools
>> Tel : 905-413-3923 T/L 969-3923
>> Fax : 905-413-4850
>> Internet ID : kalia(a)ca.ibm.com
>> ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 09:43 AM
-----
>>
>> Steve Hanson <smh(a)uk.ibm.com>
>> Sent by: owner-dfdl-wg(a)ggf.org
>> 01/19/2006 04:43 AM
>>
>> To
>> "Westhead, Martin (Martin)" <westhead(a)avaya.com>
>> cc
>> dfdl-wg(a)ggf.org, owner-dfdl-wg(a)ggf.org
>> Subject
>> Re: [dfdl-wg] Ambiguous XPaths to hidden elements
>>
>>
>>
>>
>>
>>
>> As a DFDL parser implementor I do not want modifications to the XPath
>> syntax. I want to be able to reuse existing XPath implementations.
It's
>> also something else for the user to have to learn. So 2a/b/c are not
>> attractive.
>>
>> Regards, Steve
>>
>> Steve Hanson
>> WebSphere Message Brokers,
>> IBM Hursley, England
>> Internet: smh(a)uk.ibm.com
>> Phone (+44)/(0) 1962-815848
>>
>>
>>
>> "Westhead, Martin
>> (Martin)"
>> <westhead(a)avaya.c
>To
>>
>> om> <dfdl-wg(a)ggf.org>
>> Sent by:
>cc
>>
>> owner-dfdl-wg@ggf
>> .org
>Subject
>>
>> [dfdl-wg] Ambiguous XPaths to
>> hidden elements
>> 18/01/2006 20:24
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> Hi folks,
>>
>> This is to try to pick up on the issue identified by Suman in today?s
>> call.
>>
>> The Issue
>> Consider the following example:
>>
>> <xs:element name="root">
>> <xs:complexType>
>> <xs:sequence>
>>
><xs:annotation><xs:appinfo
>> source=?http://dataformat.org? />
>> <hidden>
>> <xs:element name="repeats" type="xs:integer"/>
>>
</hidden>
>>
>> </xs:appinfo></xs:annotation >
>> <xs:element name="testElement"
>> type="xs:integer " minOccurs=?0? maxOccurs=?unbounded?
>> dfdl:repeatCount=?../repeats?>
>> </xs:complexType>
>> </xs:element>
>>
>> The problem is that the path ?../repeats? can be broken by
modifications
>> to
>> the logical model due to name clashes on ?repeats? and there are
cases
>> that
>> can be constructed where this would not be obvious to a user.
>>
>> Possible Solutions
>> Possible fixes to this include:
>> 1. Disallow XPath references to hidden elements the user is
forced
>> to
>> place the material into the global context to refer to it.
>> 2. Provide a special XPath operator to indicate we are
referencing
>> a
>> hidden element, possibilities include:
>> a. ?../hidden(repeats)?
>> b. ?hidden(../repeats)?
>> c. ?../dfdl:hidden/repeats?
>> 3. Only allow hidden elements to be present in top level global
>> complex> ysTsc ebilewrnd.Tssh
>suo
> ttSa sphg but I don?t fully understand it ?
>> in
>> particular I don?t see how it resolves the ambiguity issue.)
>>
>>
>> I believe my preference here is 2a or 2b followed by 1.
>>
>> Comments/suggestions/opinions?
>>
>> Thanks,
>>
>> Martin
>
>--
>---
>Robert E. McGrath, Ph.D.
>National Center for Supercomputing Applications
>University of Illinois, Urbana-Champaign
>1205 West Clark
>Urbana, Illinois 61801
>(217)-333-6549
>
>mcgrath(a)ncsa.uiuc.edu
2
1
20 Jan '06
Well I wasn't saying that. I was saying that you could do that if things
didn't line up.
I suppose I don't feel strongly about the restriction I just don't
really see the need.
I have a number of examples of XML which are essentially tables with
lists of elements with just attributes. I could imagine it would be easy
and convenient to populate such a logical model directly using
annotations without forcing the user to add hidden layers...
Martin
_____
From: Mike Beckerle [mailto:beckerle@us.ibm.com]
Sent: Thursday, January 19, 2006 12:55 PM
To: Westhead, Martin (Martin)
Cc: dfdl-wg(a)ggf.org; Suman Kalia; owner-dfdl-wg(a)ggf.org; Steve Hanson
Subject: RE: Attributes - (was Ambiguous XPaths to hidden elements)
I agree with you.
There is one caveat though, you are saying in effect that attributes are
only supported via population to/from other elements or attributes
(which can be hidden). The bottom layer must be elements only.
With this restriction I am fine with attributes. The vast bulk of the
DFDL spec will simply be unconcerned with them.
...mikeb
Mike Beckerle
STSM, Architect, Scalable Computing
IBM Software Group
Information Integration Solutions
Westborough, MA 01581
voice and FAX 508-599-7148
home/mobile office 508-915-4767
"Westhead, Martin \(Martin\)" <westhead(a)avaya.com>
01/19/2006 03:45 PM
To
Mike Beckerle/Worcester/IBM@IBMUS
cc
<dfdl-wg(a)ggf.org>, "Suman Kalia" <kalia(a)ca.ibm.com>,
<owner-dfdl-wg(a)ggf.org>, "Steve Hanson" <smh(a)uk.ibm.com>
Subject
RE: Attributes - (was Ambiguous XPaths to hidden elements)
Perhaps there is a discussion here for later, but with hidden elements I
don't think there's much of an issue here.
My take on this is that we are using the XSD to do more than it is
supposed to, we are not just using it to describe valid XML we are using
it constructively to describe how to build an XML instance. We are
establishing a semantics for how the DFDL parser constructs this XML
document from the XSD and the data.
Now, it is easy to imagine cases where you have a particular xml model
you want to populate which is similar to the data but is perhaps a
subset with slightly different ordering. Hidden elements make this easy
to handle. You put the stuff that is to be omitted in a hidden element.
Stuff that is out of order can be put in hidden elements and then
referenced by correctly ordered elements for value.
In this framework attributes are just another node for data population.
If it happens that you can arrange the XML Schema so that the order in
which attributes are laid out in the file corresponds to the ordering of
the data, well then its no different from elements. If there are
constraints that prevent that ordering then you are in a situation just
like the one I describe above and you solve it with hidden elements.
So I don't really disagree with your points below it just seems to me
that there's nothing much to worry about here. I can't see why we would
put it off - there's no extra work to do?
Cheers,
Martin
_____
From: Mike Beckerle [mailto:beckerle@us.ibm.com]
Sent: Thursday, January 19, 2006 12:27 PM
To: Westhead, Martin (Martin)
Cc: dfdl-wg(a)ggf.org; Suman Kalia; owner-dfdl-wg(a)ggf.org; Steve Hanson
Subject: Re: Attributes - (was Ambiguous XPaths to hidden elements)
Here's some of the issues with attributes:
1) every element can have two kinds of children now, attributes and
sub-elements. Actual DFDL-described data will typically have just one
kind of sub-fields of data, but some want to be mapped to attributes,
others to elements. How do you specify how the attributes are separated
from the elements. Do the attributes have to be first, or last, or can
they be interleaved with the sub-elements' physical data?
2) in XSD syntax, if you define a element with both sub-elements and
attributes, the attributes textually come after the sub-elements. This
means you may or may not have them in the right order for DFDL
annotation to be convenient. E.g., suppose you had 5 children the first
2 you want to be attributes the remaining 3 sub-elements in a sequence.
How can you annotate this conveniently?
3)The attributes are always unordered w.r.t. the XSD concept, but the
sub-elements can be either ordered or un-ordered.
These all seemed like avoidable issues. That is, I'm not saying there is
no good solution here, I'm just saying it's probably uninteresting.
One solution to the whole issue is to say that attributes can't be in
the bottom-most layer. I.e., you create them by referencing element
values in hidden or non-hidden layers. This eliminates all the above
problems.It is equivalent to using a stylesheet to create the attributes
you want from elements-only data. However, by use of the layers you can
embed it all right into the DFDL schema.
I also believe attributes are to some extent beside the point for DFDL.
What we needed from XSD is a standardized hierarchical type system that
we can hang represetnation properties on. We get that by using the
elements-only subset of XSD. Attributes are only needed if we broaden
our agenda to include "creating the XML I want out of my data", which
layering can do.
Mike Beckerle
STSM, Architect, Scalable Computing
IBM Software Group
Information Integration Solutions
Westborough, MA 01581
voice and FAX 508-599-7148
home/mobile office 508-915-4767
"Westhead, Martin \(Martin\)" <westhead(a)avaya.com>
01/19/2006 03:05 PM
To
Mike Beckerle/Worcester/IBM@IBMUS
cc
<dfdl-wg(a)ggf.org>, "Suman Kalia" <kalia(a)ca.ibm.com>,
<owner-dfdl-wg(a)ggf.org>, "Steve Hanson" <smh(a)uk.ibm.com>
Subject
Attributes - (was Ambiguous XPaths to hidden elements)
I think (hope) that with the emerging operational semantics, that there
will not be any problems putting annotations into attributes and having
them evaluated just like an element. It is not obvious to me that they
are any different.
Martin
_____
From: Mike Beckerle [mailto:beckerle@us.ibm.com]
Sent: Thursday, January 19, 2006 12:03 PM
To: Westhead, Martin (Martin)
Cc: dfdl-wg(a)ggf.org; Suman Kalia; owner-dfdl-wg(a)ggf.org; Steve Hanson
Subject: RE: [dfdl-wg] Ambiguous XPaths to hidden elements
I think we did not agree formally to this. It was one of those things
where we're trying to find something we can cut out with low risk of
later complications.
Mike Beckerle
STSM, Architect, Scalable Computing
IBM Software Group
Information Integration Solutions
Westborough, MA 01581
voice and FAX 508-599-7148
home/mobile office 508-915-4767
"Westhead, Martin (Martin)" <westhead(a)avaya.com>
Sent by: owner-dfdl-wg(a)ggf.org
01/19/2006 01:59 PM
To
"Suman Kalia" <kalia(a)ca.ibm.com>, "Steve Hanson" <smh(a)uk.ibm.com>
cc
Mike Beckerle/Worcester/IBM@IBMUS, <dfdl-wg(a)ggf.org>,
<owner-dfdl-wg(a)ggf.org>
Subject
RE: [dfdl-wg] Ambiguous XPaths to hidden elements
Why are we not allowing attributes?
Martin
_____
From: owner-dfdl-wg(a)ggf.org [mailto:owner-dfdl-wg@ggf.org] On Behalf Of
Suman Kalia
Sent: Thursday, January 19, 2006 10:57 AM
To: Steve Hanson
Cc: Mike Beckerle; dfdl-wg(a)ggf.org; owner-dfdl-wg(a)ggf.org
Subject: Fw: [dfdl-wg] Ambiguous XPaths to hidden elements
The main problem will be performance and excessively long validation
times and either asking the user to change their schema or model it
different way. These are all undesirable. Attributes I hope will be
supported in the future release . Redefine construct is hardly used in
the practical applications; at least I haven't come across any customer
that uses this construct ..
Suman Kalia
IBM Toronto Lab
WebSphere Business Integration Application Connectivity Tools
Tel : 905-413-3923 T/L 969-3923
Fax : 905-413-4850
Internet ID : kalia(a)ca.ibm.com
----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 01:49 PM -----
Steve Hanson <smh(a)uk.ibm.com>
01/19/2006 01:15 PM
To
Suman Kalia/Toronto/IBM@IBMCA
cc
Mike Beckerle <beckerle(a)us.ibm.com>, dfdl-wg(a)ggf.org,
owner-dfdl-wg(a)ggf.org
Subject
Re: Fw: [dfdl-wg] Ambiguous XPaths to hidden elements
We are already putting constraints on user-defined schema, by saying
that
we don't support redefines and attributes for example. I don't see an
issue
with further constraints if they make DFDL easier to understand and/or
easier to create a DFDL parser.
I don't have a problem with saying that an XPath must return a single
unambiguous node else it is an error.
I don't have a problem with saying the XPaths can't reference hidden
elements, and that context must be used instead.
Regards, Steve
Steve Hanson
WebSphere Message Brokers,
IBM Hursley, England
Internet: smh(a)uk.ibm.com
Phone (+44)/(0) 1962-815848
Suman Kalia
<kalia(a)ca.ibm.com
> To
Sent by: Mike Beckerle <beckerle(a)us.ibm.com>
owner-dfdl-wg@ggf cc
.org dfdl-wg(a)ggf.org,
owner-dfdl-wg(a)ggf.org
Subject
19/01/2006 18:02 Fw: [dfdl-wg] Ambiguous XPaths to
hidden elements
Well if we go with global complex type approach (which I described
option 1
in previous append) then it is not issue.. XPATH work and there are no
conflicts with user defined schemas ..
Suman Kalia
IBM Toronto Lab
WebSphere Business Integration Application Connectivity Tools
Tel : 905-413-3923 T/L 969-3923
Fax : 905-413-4850
Internet ID : kalia(a)ca.ibm.com
----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 12:59 PM -----
Mike
Beckerle/Worcester/IBM@IBMUS
To
01/19/2006 12:59 PM Suman Kalia/Toronto/IBM@IBMCA
cc
dfdl-wg(a)ggf.org,
owner-dfdl-wg(a)ggf.org
Subject
Re: Fw: [dfdl-wg] Ambiguous
XPaths to hidden elementsLink
So we have a quandry here:
on one hand we don't want to change the XPath syntax to include a device
that would let us be clear that we're navigating a hidden layer
on the other hand we don't want to constrain what can be included so
that
we wouldn't need such a device.
...mikeb
Mike Beckerle
STSM, Architect, Scalable Computing
IBM Software Group
Information Integration Solutions
Westborough, MA 01581
voice and FAX 508-599-7148
home/mobile office 508-915-4767
Suman Kalia/Toronto/IBM@IBMCA
01/19/2006 11:52 AM
To
Mike
Beckerle/Worcester/IBM@IBMUS
cc
dfdl-wg(a)ggf.org,
owner-dfdl-wg(a)ggf.org
Subject
Fw: [dfdl-wg] Ambiguous
XPaths to hidden elements
As a design point , We should strive not to put limitations on the user
defined schemas - it just works out better in the long run.
Note the xsd:groups can be nested and they could be many levels deep and
this problem is not restricted to groups included from noTarget
namespace
, it could be from any namespace. As per schema rules, all local
elements
defined in groups or complex types belong to noTarget namespace unless
elementFormDefault is explicitly set to "qualified" at schema level or
on
the specific element.
Detecting such conflicts could be quite expensive particularly when you
have very large schemas. Industry standard ACORD messaging schema is a
good example it is about 1.5 M and it takes awfully long (hours) to
validate it. Putting additional constraints like this will further slow
down validation.
Suman Kalia
IBM Toronto Lab
WebSphere Business Integration Application Connectivity Tools
Tel : 905-413-3923 T/L 969-3923
Fax : 905-413-4850
Internet ID : kalia(a)ca.ibm.com
----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 11:39 AM -----
Mike Beckerle
<beckerle(a)us.ibm.com>
Sent by: owner-dfdl-wg(a)ggf.org
To
"Robert E. McGrath"
01/19/2006 10:48 AM <mcgrath(a)ncsa.uiuc.edu>
cc
dfdl-wg(a)ggf.org,
owner-dfdl-wg(a)ggf.org
Subject
Re: Fw: [dfdl-wg] Ambiguous
XPaths to hidden elements
One idea that hasn't been advanced yet is ruling out the problematic
case.
Let me illustrate. Here's the example, modified to have a model group
reference which can introduce the name conflict:
<xs:element name="root">
<xs:complexType>
<xs:sequence>
<xs:annotation><xs:appinfo
source="http://dataformat.org" />
<hidden>
<xs:element name="repeats" type="xs:integer"/>
</hidden>
</xs:appinfo></xs:annotation
>
<xs:element name="testElement"
type="xs:integer " minOccurs="0" maxOccurs="unbounded"
dfdl:repeatCount="../repeats">
<xs:group ref="groupFromOtherSchemaFile"/>
<!-- what if this has an element decl named "repeats"? -->
</xs:complexType>
</xs:element>
So, what hasn't been suggested yet is this: What if we just say DFDL
doesn't allow this? It's an error which must be detected. This DFDL
schema
is broken because the path "../repeats" cannot be analyzed along with
the
DFDL schema to return only a single node.
I beleive name conflicts like this are what namespace management is for.
XSD has truly great namespace managment. You can solve the problem that
way.
Furthermore, when you define a reusable named group like the definer of
the
"groupFromOtherSchemaFile" above, and you put it in no target namespace,
that's the situation where this conflict can arise. Expecting that your
names are never going to conflict with anything in that case is just
naive.
It's equivalent to having global variables in a C program module and
expecting you can never link it to something else that uses the same
names.
Those name conflicts can occur, and someone has to change the
conflicting
name. In XSD we can do that by including the group in a schema which
puts
it into a target namespace so that after that the namespaces can be used
to
disambiguate.
The approach above is consistent with the path "../repeats" still being
officialy an "XPath", it just adds the semantic restriction that it must
be
an XPath that identifies a single node unambiguously, independent of
what
data is being processed. This is one of these "data independent" notions
(what I had previously been calling "static"), as we discussed
yesterday.
...mikeb
"Robert E. McGrath"
<mcgrath(a)ncsa.uiuc.edu>
Sent by: owner-dfdl-wg(a)ggf.org
To
dfdl-wg(a)ggf.org
01/19/2006 10:00 AM
cc
Subject
Re: Fw: [dfdl-wg]
Ambiguous XPaths to hidden
elements
I would want to change XPath only as a last resort. (Any of the
options is OK by me, assuming we have to mess with the Xpath
at all.)
Can we deal with this some other way?
Can we document the problematic cases, and suggest best practices that
will minimize the problem?
On Thursday 19 January 2006 08:45, Suman Kalia wrote:
> I fully agree with Steve - let's not invent another XPATH like syntax
..
>
> Suman Kalia
> IBM Toronto Lab
> WebSphere Business Integration Application Connectivity Tools
> Tel : 905-413-3923 T/L 969-3923
> Fax : 905-413-4850
> Internet ID : kalia(a)ca.ibm.com
> ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 09:43 AM
-----
>
> Steve Hanson <smh(a)uk.ibm.com>
> Sent by: owner-dfdl-wg(a)ggf.org
> 01/19/2006 04:43 AM
>
> To
> "Westhead, Martin (Martin)" <westhead(a)avaya.com>
> cc
> dfdl-wg(a)ggf.org, owner-dfdl-wg(a)ggf.org
> Subject
> Re: [dfdl-wg] Ambiguous XPaths to hidden elements
>
>
>
>
>
>
> As a DFDL parser implementor I do not want modifications to the XPath
> syntax. I want to be able to reuse existing XPath implementations.
It's
> also something else for the user to have to learn. So 2a/b/c are not
> attractive.
>
> Regards, Steve
>
> Steve Hanson
> WebSphere Message Brokers,
> IBM Hursley, England
> Internet: smh(a)uk.ibm.com
> Phone (+44)/(0) 1962-815848
>
>
>
> "Westhead, Martin
> (Martin)"
> <westhead(a)avaya.c
To
>
> om> <dfdl-wg(a)ggf.org>
> Sent by:
cc
>
> owner-dfdl-wg@ggf
> .org
Subject
>
> [dfdl-wg] Ambiguous XPaths to
> hidden elements
> 18/01/2006 20:24
>
>
>
>
>
>
>
>
>
> Hi folks,
>
> This is to try to pick up on the issue identified by Suman in today?s
> call.
>
> The Issue
> Consider the following example:
>
> <xs:element name="root">
> <xs:complexType>
> <xs:sequence>
>
<xs:annotation><xs:appinfo
> source=?http://dataformat.org? />
> <hidden>
> <xs:element name="repeats" type="xs:integer"/>
>
</hidden>
>
> </xs:appinfo></xs:annotation >
> <xs:element name="testElement"
> type="xs:integer " minOccurs=?0? maxOccurs=?unbounded?
> dfdl:repeatCount=?../repeats?>
> </xs:complexType>
> </xs:element>
>
> The problem is that the path ?../repeats? can be broken by
modifications
> to
> the logical model due to name clashes on ?repeats? and there are cases
> that
> can be constructed where this would not be obvious to a user.
>
> Possible Solutions
> Possible fixes to this include:
> 1. Disallow XPath references to hidden elements the user is
forced
> to
> place the material into the global context to refer to it.
> 2. Provide a special XPath operator to indicate we are
referencing
> a
> hidden element, possibilities include:
> a. ?../hidden(repeats)?
> b. ?hidden(../repeats)?
> c. ?../dfdl:hidden/repeats?
> 3. Only allow hidden elements to be present in top level global
> complex
> types. These can then be included where needed. (This is the
> solution
> that Suman was pushing but I don?t fully understand it
?
> in
> particular I don?t see how it resolves the ambiguity issue.)
>
>
> I believe my preference here is 2a or 2b followed by 1.
>
> Comments/suggestions/opinions?
>
> Thanks,
>
> Martin
--
---
Robert E. McGrath, Ph.D.
National Center for Supercomputing Applications
University of Illinois, Urbana-Champaign
1205 West Clark
Urbana, Illinois 61801
(217)-333-6549
mcgrath(a)ncsa.uiuc.edu
2
1
(oops. sent this just to martin. This to the whole group.)
Global context just makes the name clash problem much worse.
You'll end up with the global names having to be structured like
com.ibm.mydepartment.myname in order to avoid the conflicts.
Even then you have reentrancy to deal with. (Types can be recursively
defined in XSD)
I believe we need to discuss concrete code snippets to clarify this issue.
...mikeb
Mike Beckerle
STSM, Architect, Scalable Computing
IBM Software Group
Information Integration Solutions
Westborough, MA 01581
voice and FAX 508-599-7148
home/mobile office 508-915-4767
"Westhead, Martin \(Martin\)" <westhead(a)avaya.com>
01/19/2006 02:20 PM
To
"Robert E. McGrath" <mcgrath(a)ncsa.uiuc.edu>, "Suman Kalia"
<kalia(a)ca.ibm.com>, "Steve Hanson" <smh(a)uk.ibm.com>
cc
Mike Beckerle/Worcester/IBM@IBMUS, <dfdl-wg(a)ggf.org>
Subject
RE: Fw: [dfdl-wg] Ambiguous XPaths to hidden elements
I think this discussion is getting a little snarled. To clarify:
If I understood Suman correctly he is happy with option 1 which was: You
cannot reference hidden elements outside the <hidden> using XPath. To
reference the hidden element you have to place it into the global
context.
Does anyone have any serious objections to this proposal?
Martin
>-----Original Message-----
>From: owner-dfdl-wg(a)ggf.org [mailto:owner-dfdl-wg@ggf.org] On Behalf Of
>Robert E. McGrath
>Sent: Thursday, January 19, 2006 11:16 AM
>To: Suman Kalia; Steve Hanson
>Cc: Mike Beckerle; dfdl-wg(a)ggf.org
>Subject: Re: Fw: [dfdl-wg] Ambiguous XPaths to hidden elements
>
>I don't know how to deal with this. We can't really make decisions
based
>on anticipated performance issues in software that most of us have no
>knowledge about.
>
>One way or another, we have to support this context.
>
>As Steve said, we already have limited the schema. I suspect
>we will find more limitations before we are done. Either of the
>approaches that Steve posed are OK with me.
>
>On Thursday 19 January 2006 12:56, Suman Kalia wrote:
>> The main problem will be performance and excessively long validation
>times
>> and either asking the user to change their schema or model it
different
>> way. These are all undesirable. Attributes I hope will be supported
in
>> the future release . Redefine construct is hardly used in the
practical
>> applications; at least I haven't come across any customer that uses
this
>> construct ..
>>
>> Suman Kalia
>> IBM Toronto Lab
>> WebSphere Business Integration Application Connectivity Tools
>> Tel : 905-413-3923 T/L 969-3923
>> Fax : 905-413-4850
>> Internet ID : kalia(a)ca.ibm.com
>> ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 01:49 PM
-----
>>
>> Steve Hanson <smh(a)uk.ibm.com>
>> 01/19/2006 01:15 PM
>>
>> To
>> Suman Kalia/Toronto/IBM@IBMCA
>> cc
>> Mike Beckerle <beckerle(a)us.ibm.com>, dfdl-wg(a)ggf.org,
>> owner-dfdl-wg(a)ggf.org
>> Subject
>> Re: Fw: [dfdl-wg] Ambiguous XPaths to hidden elements
>>
>>
>>
>>
>>
>>
>> We are already putting constraints on user-defined schema, by saying
that
>> we don't support redefines and attributes for example. I don't see an
>> issue
>> with further constraints if they make DFDL easier to understand
and/or
>> easier to create a DFDL parser.
>>
>> I don't have a problem with saying that an XPath must return a single
>> unambiguous node else it is an error.
>> I don't have a problem with saying the XPaths can't reference hidden
>> elements, and that context must be used instead.
>>
>> Regards, Steve
>>
>> Steve Hanson
>> WebSphere Message Brokers,
>> IBM Hursley, England
>> Internet: smh(a)uk.ibm.com
>> Phone (+44)/(0) 1962-815848
>>
>>
>>
>> Suman Kalia
>> <kalia(a)ca.ibm.com
>>
>> >
>To
>>
>> Sent by: Mike Beckerle
><beckerle(a)us.ibm.com>
>>
>> owner-dfdl-wg@ggf
>cc
>>
>> .org dfdl-wg(a)ggf.org,
>> owner-dfdl-wg(a)ggf.org
>>
>Subject
>>
>> 19/01/2006 18:02 Fw: [dfdl-wg] Ambiguous XPaths
to
>> hidden elements
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> Well if we go with global complex type approach (which I described
option
>> 1
>> in previous append) then it is not issue.. XPATH work and there are
no
>> conflicts with user defined schemas ..
>>
>> Suman Kalia
>> IBM Toronto Lab
>> WebSphere Business Integration Application Connectivity Tools
>> Tel : 905-413-3923 T/L 969-3923
>> Fax : 905-413-4850
>> Internet ID : kalia(a)ca.ibm.com
>> ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 12:59 PM
-----
>>
>> Mike
>> Beckerle/Worcester/IBM@IBMUS
>>
>>
>To
>>
>> 01/19/2006 12:59 PM Suman
Kalia/Toronto/IBM@IBMCA
>>
>cc
>>
>> dfdl-wg(a)ggf.org,
>> owner-dfdl-wg(a)ggf.org
>>
>Subject
>>
>> Re: Fw: [dfdl-wg]
Ambiguous
>> XPaths to hidden
elementsLink
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> So we have a quandry here:
>>
>> on one hand we don't want to change the XPath syntax to include a
device
>> that would let us be clear that we're navigating a hidden layer
>>
>> on the other hand we don't want to constrain what can be included so
that
>> we wouldn't need such a device.
>>
>> ...mikeb
>>
>> Mike Beckerle
>> STSM, Architect, Scalable Computing
>> IBM Software Group
>> Information Integration Solutions
>> Westborough, MA 01581
>> voice and FAX 508-599-7148
>> home/mobile office 508-915-4767
>>
>>
>>
>>
>> Suman Kalia/Toronto/IBM@IBMCA
>>
>>
>> 01/19/2006 11:52 AM
>To
>>
>> Mike
>>
Beckerle/Worcester/IBM@IBMUS
>>
>cc
>>
>> dfdl-wg(a)ggf.org,
>> owner-dfdl-wg(a)ggf.org
>>
>Subject
>>
>> Fw: [dfdl-wg] Ambiguous
>> XPaths to hidden
elements
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> As a design point , We should strive not to put limitations on the
user
>> defined schemas - it just works out better in the long run.
>>
>> Note the xsd:groups can be nested and they could be many levels deep
and
>> this problem is not restricted to groups included from noTarget
>namespace
>> , it could be from any namespace. As per schema rules, all local
>elements
>> defined in groups or complex types belong to noTarget namespace
unless
>> elementFormDefault is explicitly set to "qualified" at schema level
or on
>> the specific element.
>>
>> Detecting such conflicts could be quite expensive particularly when
you
>> have very large schemas. Industry standard ACORD messaging schema is
a
>> good example it is about 1.5 M and it takes awfully long (hours) to
>> validate it. Putting additional constraints like this will further
slow
>> down validation.
>>
>> Suman Kalia
>> IBM Toronto Lab
>> WebSphere Business Integration Application Connectivity Tools
>> Tel : 905-413-3923 T/L 969-3923
>> Fax : 905-413-4850
>> Internet ID : kalia(a)ca.ibm.com
>> ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 11:39 AM
-----
>>
>> Mike Beckerle
>> <beckerle(a)us.ibm.com>
>> Sent by: owner-dfdl-wg(a)ggf.org
>>
>To
>>
>> "Robert E. McGrath"
>> 01/19/2006 10:48 AM <mcgrath(a)ncsa.uiuc.edu>
>>
>cc
>>
>> dfdl-wg(a)ggf.org,
>> owner-dfdl-wg(a)ggf.org
>>
>Subject
>>
>> Re: Fw: [dfdl-wg]
Ambiguous
>> XPaths to hidden
elements
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> One idea that hasn't been advanced yet is ruling out the problematic
>case.
>>
>> Let me illustrate. Here's the example, modified to have a model group
>> reference which can introduce the name conflict:
>>
>> <xs:element name="root">
>> <xs:complexType>
>> <xs:sequence>
>>
<xs:annotation><xs:appinfo
>> source=?http://dataformat.org? />
>> <hidden>
>>
>> <xs:element name="repeats" type="xs:integer"/>
>>
</hidden>
>> </xs:appinfo></xs:annotation
>>
>> <xs:element name="testElement"
>> type="xs:integer " minOccurs=?0? maxOccurs=?unbounded?
>> dfdl:repeatCount=?../repeats?>
>>
>> <xs:group
ref="groupFromOtherSchemaFile"/>
>> <!-- what if this has an element decl named "repeats"? -->
>>
>> </xs:complexType>
>> </xs:element>
>>
>> So, what hasn't been suggested yet is this: What if we just say DFDL
>> doesn't allow this? It's an error which must be detected. This DFDL
>schema
>> is broken because the path "../repeats" cannot be analyzed along with
the
>> DFDL schema to return only a single node.
>>
>> I beleive name conflicts like this are what namespace management is
for.
>> XSD has truly great namespace managment. You can solve the problem
that
>> way.
>>
>> Furthermore, when you define a reusable named group like the definer
of
>> the
>> "groupFromOtherSchemaFile" above, and you put it in no target
namespace,
>> that's the situation where this conflict can arise. Expecting that
your
>> names are never going to conflict with anything in that case is just
>> naive.
>> It's equivalent to having global variables in a C program module and
>> expecting you can never link it to something else that uses the same
>> names.
>> Those name conflicts can occur, and someone has to change the
conflicting
>> name. In XSD we can do that by including the group in a schema which
puts
>> it into a target namespace so that after that the namespaces can be
used
>> to
>> disambiguate.
>>
>> The approach above is consistent with the path "../repeats" still
being
>> officialy an "XPath", it just adds the semantic restriction that it
must
>> be
>> an XPath that identifies a single node unambiguously, independent of
what
>> data is being processed. This is one of these "data independent"
notions
>> (what I had previously been calling "static"), as we discussed
yesterday.
>>
>> ...mikeb
>>
>>
>>
>>
>> "Robert E. McGrath"
>> <mcgrath(a)ncsa.uiuc.edu>
>> Sent by: owner-dfdl-wg(a)ggf.org
>>
>To
>>
>> dfdl-wg(a)ggf.org
>> 01/19/2006 10:00 AM
>cc
>>
>>
>>
>Subject
>>
>> Re: Fw: [dfdl-wg]
>> Ambiguous XPaths to
>hidden
>>
>> elements
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> I would want to change XPath only as a last resort. (Any of the
>> options is OK by me, assuming we have to mess with the Xpath
>> at all.)
>>
>> Can we deal with this some other way?
>>
>> Can we document the problematic cases, and suggest best practices
that
>> will minimize the problem?
>>
>> On Thursday 19 January 2006 08:45, Suman Kalia wrote:
>> > I fully agree with Steve - let's not invent another XPATH like
syntax
>..
>> >
>> > Suman Kalia
>> > IBM Toronto Lab
>> > WebSphere Business Integration Application Connectivity Tools
>> > Tel : 905-413-3923 T/L 969-3923
>> > Fax : 905-413-4850
>> > Internet ID : kalia(a)ca.ibm.com
>> > ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 09:43 AM
-----
>> >
>> > Steve Hanson <smh(a)uk.ibm.com>
>> > Sent by: owner-dfdl-wg(a)ggf.org
>> > 01/19/2006 04:43 AM
>> >
>> > To
>> > "Westhead, Martin (Martin)" <westhead(a)avaya.com>
>> > cc
>> > dfdl-wg(a)ggf.org, owner-dfdl-wg(a)ggf.org
>> > Subject
>> > Re: [dfdl-wg] Ambiguous XPaths to hidden elements
>> >
>> >
>> >
>> >
>> >
>> >
>> > As a DFDL parser implementor I do not want modifications to the
XPath
>> > syntax. I want to be able to reuse existing XPath implementations.
It's
>> > also something else for the user to have to learn. So 2a/b/c are
not
>> > attractive.
>> >
>> > Regards, Steve
>> >
>> > Steve Hanson
>> > WebSphere Message Brokers,
>> > IBM Hursley, England
>> > Internet: smh(a)uk.ibm.com
>> > Phone (+44)/(0) 1962-815848
>> >
>> >
>> >
>> > "Westhead, Martin
>> > (Martin)"
>> > <westhead(a)avaya.c
>>
>> To
>>
>> > om> <dfdl-wg(a)ggf.org>
>> > Sent by:
>>
>> cc
>>
>> > owner-dfdl-wg@ggf
>> > .org
>>
>> Subject
>>
>> > [dfdl-wg] Ambiguous XPaths
to
>> > hidden elements
>> > 18/01/2006 20:24
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> > Hi folks,
>> >
>> > This is to try to pick up on the issue identified by Suman in
today?s
>> > call.
>> >
>> > The Issue
>> > Consider the following example:
>> >
>> > <xs:element name="root">
>> > <xs:complexType>
>> > <xs:sequence>
>>
>> <xs:annotation><xs:appinfo
>>
>> > source=?http://dataformat.org? />
>> > <hidden>
>> > <xs:element name="repeats" type="xs:integer"/>
>> > </hidden>
>> >
>> > </xs:appinfo></xs:annotation >
>> > <xs:element name="testElement"
>> > type="xs:integer " minOccurs=?0? maxOccurs=?unbounded?
>> > dfdl:repeatCount=?../repeats?>
>> > </xs:complexType>
>> > </xs:element>
>> >
>> > The problem is that the path ?../repeats? can be broken by
>modifications
>> > to
>> > the logical model due to name clashes on ?repeats? and there are
cases
>> > that
>> > can be constructed where this would not be obvious to a user.
>> >
>> > Possible Solutions
>> > Possible fixes to this include:
>> > 1. Disallow XPath references to hidden elements the user is
>forced
>> > to
>> > place the material into the global context to refer to it.
>> > 2. Provide a special XPath operator to indicate we are
>>
>> referencing
>>
>> > a
>> > hidden element, possibilities include:
>> > a. ?../hidden(repeats)?
>> > b. ?hidden(../repeats)?
>> > c. ?../dfdl:hidden/repeats?
>> > 3. Only allow hidden elements to be present in top level global
>> > complex
>> > types. These can then be included where needed. (This is the
>> > solution
>> > that Suman was pushing but I don?t fully understand
it
>?
>> > in
>> > particular I don?t see how it resolves the ambiguity issue.)
>> >
>> >
>> > I believe my preference here is 2a or 2b followed by 1.
>> >
>> > Comments/suggestions/opinions?
>> >
>> > Thanks,
>> >
>> > Martin
>>
>> --
>> ---
>> Robert E. McGrath, Ph.D.
>> National Center for Supercomputing Applications
>> University of Illinois, Urbana-Champaign
>> 1205 West Clark
>> Urbana, Illinois 61801
>> (217)-333-6549
>>
>> mcgrath(a)ncsa.uiuc.edu
>
>--
>---
>Robert E. McGrath, Ph.D.
>National Center for Supercomputing Applications
>University of Illinois, Urbana-Champaign
>1205 West Clark
>Urbana, Illinois 61801
>(217)-333-6549
>
>mcgrath(a)ncsa.uiuc.edu
1
0
19 Jan '06
Perhaps there is a discussion here for later, but with hidden elements I
don't think there's much of an issue here.
My take on this is that we are using the XSD to do more than it is
supposed to, we are not just using it to describe valid XML we are using
it constructively to describe how to build an XML instance. We are
establishing a semantics for how the DFDL parser constructs this XML
document from the XSD and the data.
Now, it is easy to imagine cases where you have a particular xml model
you want to populate which is similar to the data but is perhaps a
subset with slightly different ordering. Hidden elements make this easy
to handle. You put the stuff that is to be omitted in a hidden element.
Stuff that is out of order can be put in hidden elements and then
referenced by correctly ordered elements for value.
In this framework attributes are just another node for data population.
If it happens that you can arrange the XML Schema so that the order in
which attributes are laid out in the file corresponds to the ordering of
the data, well then its no different from elements. If there are
constraints that prevent that ordering then you are in a situation just
like the one I describe above and you solve it with hidden elements.
So I don't really disagree with your points below it just seems to me
that there's nothing much to worry about here. I can't see why we would
put it off - there's no extra work to do?
Cheers,
Martin
_____
From: Mike Beckerle [mailto:beckerle@us.ibm.com]
Sent: Thursday, January 19, 2006 12:27 PM
To: Westhead, Martin (Martin)
Cc: dfdl-wg(a)ggf.org; Suman Kalia; owner-dfdl-wg(a)ggf.org; Steve Hanson
Subject: Re: Attributes - (was Ambiguous XPaths to hidden elements)
Here's some of the issues with attributes:
1) every element can have two kinds of children now, attributes and
sub-elements. Actual DFDL-described data will typically have just one
kind of sub-fields of data, but some want to be mapped to attributes,
others to elements. How do you specify how the attributes are separated
from the elements. Do the attributes have to be first, or last, or can
they be interleaved with the sub-elements' physical data?
2) in XSD syntax, if you define a element with both sub-elements and
attributes, the attributes textually come after the sub-elements. This
means you may or may not have them in the right order for DFDL
annotation to be convenient. E.g., suppose you had 5 children the first
2 you want to be attributes the remaining 3 sub-elements in a sequence.
How can you annotate this conveniently?
3)The attributes are always unordered w.r.t. the XSD concept, but the
sub-elements can be either ordered or un-ordered.
These all seemed like avoidable issues. That is, I'm not saying there is
no good solution here, I'm just saying it's probably uninteresting.
One solution to the whole issue is to say that attributes can't be in
the bottom-most layer. I.e., you create them by referencing element
values in hidden or non-hidden layers. This eliminates all the above
problems.It is equivalent to using a stylesheet to create the attributes
you want from elements-only data. However, by use of the layers you can
embed it all right into the DFDL schema.
I also believe attributes are to some extent beside the point for DFDL.
What we needed from XSD is a standardized hierarchical type system that
we can hang represetnation properties on. We get that by using the
elements-only subset of XSD. Attributes are only needed if we broaden
our agenda to include "creating the XML I want out of my data", which
layering can do.
Mike Beckerle
STSM, Architect, Scalable Computing
IBM Software Group
Information Integration Solutions
Westborough, MA 01581
voice and FAX 508-599-7148
home/mobile office 508-915-4767
"Westhead, Martin \(Martin\)" <westhead(a)avaya.com>
01/19/2006 03:05 PM
To
Mike Beckerle/Worcester/IBM@IBMUS
cc
<dfdl-wg(a)ggf.org>, "Suman Kalia" <kalia(a)ca.ibm.com>,
<owner-dfdl-wg(a)ggf.org>, "Steve Hanson" <smh(a)uk.ibm.com>
Subject
Attributes - (was Ambiguous XPaths to hidden elements)
I think (hope) that with the emerging operational semantics, that there
will not be any problems putting annotations into attributes and having
them evaluated just like an element. It is not obvious to me that they
are any different.
Martin
_____
From: Mike Beckerle [mailto:beckerle@us.ibm.com]
Sent: Thursday, January 19, 2006 12:03 PM
To: Westhead, Martin (Martin)
Cc: dfdl-wg(a)ggf.org; Suman Kalia; owner-dfdl-wg(a)ggf.org; Steve Hanson
Subject: RE: [dfdl-wg] Ambiguous XPaths to hidden elements
I think we did not agree formally to this. It was one of those things
where we're trying to find something we can cut out with low risk of
later complications.
Mike Beckerle
STSM, Architect, Scalable Computing
IBM Software Group
Information Integration Solutions
Westborough, MA 01581
voice and FAX 508-599-7148
home/mobile office 508-915-4767
"Westhead, Martin (Martin)" <westhead(a)avaya.com>
Sent by: owner-dfdl-wg(a)ggf.org
01/19/2006 01:59 PM
To
"Suman Kalia" <kalia(a)ca.ibm.com>, "Steve Hanson" <smh(a)uk.ibm.com>
cc
Mike Beckerle/Worcester/IBM@IBMUS, <dfdl-wg(a)ggf.org>,
<owner-dfdl-wg(a)ggf.org>
Subject
RE: [dfdl-wg] Ambiguous XPaths to hidden elements
Why are we not allowing attributes?
Martin
_____
From: owner-dfdl-wg(a)ggf.org [mailto:owner-dfdl-wg@ggf.org] On Behalf Of
Suman Kalia
Sent: Thursday, January 19, 2006 10:57 AM
To: Steve Hanson
Cc: Mike Beckerle; dfdl-wg(a)ggf.org; owner-dfdl-wg(a)ggf.org
Subject: Fw: [dfdl-wg] Ambiguous XPaths to hidden elements
The main problem will be performance and excessively long validation
times and either asking the user to change their schema or model it
different way. These are all undesirable. Attributes I hope will be
supported in the future release . Redefine construct is hardly used in
the practical applications; at least I haven't come across any customer
that uses this construct ..
Suman Kalia
IBM Toronto Lab
WebSphere Business Integration Application Connectivity Tools
Tel : 905-413-3923 T/L 969-3923
Fax : 905-413-4850
Internet ID : kalia(a)ca.ibm.com
----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 01:49 PM -----
Steve Hanson <smh(a)uk.ibm.com>
01/19/2006 01:15 PM
To
Suman Kalia/Toronto/IBM@IBMCA
cc
Mike Beckerle <beckerle(a)us.ibm.com>, dfdl-wg(a)ggf.org,
owner-dfdl-wg(a)ggf.org
Subject
Re: Fw: [dfdl-wg] Ambiguous XPaths to hidden elements
We are already putting constraints on user-defined schema, by saying
that
we don't support redefines and attributes for example. I don't see an
issue
with further constraints if they make DFDL easier to understand and/or
easier to create a DFDL parser.
I don't have a problem with saying that an XPath must return a single
unambiguous node else it is an error.
I don't have a problem with saying the XPaths can't reference hidden
elements, and that context must be used instead.
Regards, Steve
Steve Hanson
WebSphere Message Brokers,
IBM Hursley, England
Internet: smh(a)uk.ibm.com
Phone (+44)/(0) 1962-815848
Suman Kalia
<kalia(a)ca.ibm.com
> To
Sent by: Mike Beckerle <beckerle(a)us.ibm.com>
owner-dfdl-wg@ggf cc
.org dfdl-wg(a)ggf.org,
owner-dfdl-wg(a)ggf.org
Subject
19/01/2006 18:02 Fw: [dfdl-wg] Ambiguous XPaths to
hidden elements
Well if we go with global complex type approach (which I described
option 1
in previous append) then it is not issue.. XPATH work and there are no
conflicts with user defined schemas ..
Suman Kalia
IBM Toronto Lab
WebSphere Business Integration Application Connectivity Tools
Tel : 905-413-3923 T/L 969-3923
Fax : 905-413-4850
Internet ID : kalia(a)ca.ibm.com
----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 12:59 PM -----
Mike
Beckerle/Worcester/IBM@IBMUS
To
01/19/2006 12:59 PM Suman Kalia/Toronto/IBM@IBMCA
cc
dfdl-wg(a)ggf.org,
owner-dfdl-wg(a)ggf.org
Subject
Re: Fw: [dfdl-wg] Ambiguous
XPaths to hidden elementsLink
So we have a quandry here:
on one hand we don't want to change the XPath syntax to include a device
that would let us be clear that we're navigating a hidden layer
on the other hand we don't want to constrain what can be included so
that
we wouldn't need such a device.
...mikeb
Mike Beckerle
STSM, Architect, Scalable Computing
IBM Software Group
Information Integration Solutions
Westborough, MA 01581
voice and FAX 508-599-7148
home/mobile office 508-915-4767
Suman Kalia/Toronto/IBM@IBMCA
01/19/2006 11:52 AM
To
Mike
Beckerle/Worcester/IBM@IBMUS
cc
dfdl-wg(a)ggf.org,
owner-dfdl-wg(a)ggf.org
Subject
Fw: [dfdl-wg] Ambiguous
XPaths to hidden elements
As a design point , We should strive not to put limitations on the user
defined schemas - it just works out better in the long run.
Note the xsd:groups can be nested and they could be many levels deep and
this problem is not restricted to groups included from noTarget
namespace
, it could be from any namespace. As per schema rules, all local
elements
defined in groups or complex types belong to noTarget namespace unless
elementFormDefault is explicitly set to "qualified" at schema level or
on
the specific element.
Detecting such conflicts could be quite expensive particularly when you
have very large schemas. Industry standard ACORD messaging schema is a
good example it is about 1.5 M and it takes awfully long (hours) to
validate it. Putting additional constraints like this will further slow
down validation.
Suman Kalia
IBM Toronto Lab
WebSphere Business Integration Application Connectivity Tools
Tel : 905-413-3923 T/L 969-3923
Fax : 905-413-4850
Internet ID : kalia(a)ca.ibm.com
----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 11:39 AM -----
Mike Beckerle
<beckerle(a)us.ibm.com>
Sent by: owner-dfdl-wg(a)ggf.org
To
"Robert E. McGrath"
01/19/2006 10:48 AM <mcgrath(a)ncsa.uiuc.edu>
cc
dfdl-wg(a)ggf.org,
owner-dfdl-wg(a)ggf.org
Subject
Re: Fw: [dfdl-wg] Ambiguous
XPaths to hidden elements
One idea that hasn't been advanced yet is ruling out the problematic
case.
Let me illustrate. Here's the example, modified to have a model group
reference which can introduce the name conflict:
<xs:element name="root">
<xs:complexType>
<xs:sequence>
<xs:annotation><xs:appinfo
source="http://dataformat.org" />
<hidden>
<xs:element name="repeats" type="xs:integer"/>
</hidden>
</xs:appinfo></xs:annotation
>
<xs:element name="testElement"
type="xs:integer " minOccurs="0" maxOccurs="unbounded"
dfdl:repeatCount="../repeats">
<xs:group ref="groupFromOtherSchemaFile"/>
<!-- what if this has an element decl named "repeats"? -->
</xs:complexType>
</xs:element>
So, what hasn't been suggested yet is this: What if we just say DFDL
doesn't allow this? It's an error which must be detected. This DFDL
schema
is broken because the path "../repeats" cannot be analyzed along with
the
DFDL schema to return only a single node.
I beleive name conflicts like this are what namespace management is for.
XSD has truly great namespace managment. You can solve the problem that
way.
Furthermore, when you define a reusable named group like the definer of
the
"groupFromOtherSchemaFile" above, and you put it in no target namespace,
that's the situation where this conflict can arise. Expecting that your
names are never going to conflict with anything in that case is just
naive.
It's equivalent to having global variables in a C program module and
expecting you can never link it to something else that uses the same
names.
Those name conflicts can occur, and someone has to change the
conflicting
name. In XSD we can do that by including the group in a schema which
puts
it into a target namespace so that after that the namespaces can be used
to
disambiguate.
The approach above is consistent with the path "../repeats" still being
officialy an "XPath", it just adds the semantic restriction that it must
be
an XPath that identifies a single node unambiguously, independent of
what
data is being processed. This is one of these "data independent" notions
(what I had previously been calling "static"), as we discussed
yesterday.
...mikeb
"Robert E. McGrath"
<mcgrath(a)ncsa.uiuc.edu>
Sent by: owner-dfdl-wg(a)ggf.org
To
dfdl-wg(a)ggf.org
01/19/2006 10:00 AM
cc
Subject
Re: Fw: [dfdl-wg]
Ambiguous XPaths to hidden
elements
I would want to change XPath only as a last resort. (Any of the
options is OK by me, assuming we have to mess with the Xpath
at all.)
Can we deal with this some other way?
Can we document the problematic cases, and suggest best practices that
will minimize the problem?
On Thursday 19 January 2006 08:45, Suman Kalia wrote:
> I fully agree with Steve - let's not invent another XPATH like syntax
..
>
> Suman Kalia
> IBM Toronto Lab
> WebSphere Business Integration Application Connectivity Tools
> Tel : 905-413-3923 T/L 969-3923
> Fax : 905-413-4850
> Internet ID : kalia(a)ca.ibm.com
> ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 09:43 AM
-----
>
> Steve Hanson <smh(a)uk.ibm.com>
> Sent by: owner-dfdl-wg(a)ggf.org
> 01/19/2006 04:43 AM
>
> To
> "Westhead, Martin (Martin)" <westhead(a)avaya.com>
> cc
> dfdl-wg(a)ggf.org, owner-dfdl-wg(a)ggf.org
> Subject
> Re: [dfdl-wg] Ambiguous XPaths to hidden elements
>
>
>
>
>
>
> As a DFDL parser implementor I do not want modifications to the XPath
> syntax. I want to be able to reuse existing XPath implementations.
It's
> also something else for the user to have to learn. So 2a/b/c are not
> attractive.
>
> Regards, Steve
>
> Steve Hanson
> WebSphere Message Brokers,
> IBM Hursley, England
> Internet: smh(a)uk.ibm.com
> Phone (+44)/(0) 1962-815848
>
>
>
> "Westhead, Martin
> (Martin)"
> <westhead(a)avaya.c
To
>
> om> <dfdl-wg(a)ggf.org>
> Sent by:
cc
>
> owner-dfdl-wg@ggf
> .org
Subject
>
> [dfdl-wg] Ambiguous XPaths to
> hidden elements
> 18/01/2006 20:24
>
>
>
>
>
>
>
>
>
> Hi folks,
>
> This is to try to pick up on the issue identified by Suman in today?s
> call.
>
> The Issue
> Consider the following example:
>
> <xs:element name="root">
> <xs:complexType>
> <xs:sequence>
>
<xs:annotation><xs:appinfo
> source=?http://dataformat.org? />
> <hidden>
> <xs:element name="repeats" type="xs:integer"/>
>
</hidden>
>
> </xs:appinfo></xs:annotation >
> <xs:element name="testElement"
> type="xs:integer " minOccurs=?0? maxOccurs=?unbounded?
> dfdl:repeatCount=?../repeats?>
> </xs:complexType>
> </xs:element>
>
> The problem is that the path ?../repeats? can be broken by
modifications
> to
> the logical model due to name clashes on ?repeats? and there are cases
> that
> can be constructed where this would not be obvious to a user.
>
> Possible Solutions
> Possible fixes to this include:
> 1. Disallow XPath references to hidden elements the user is
forced
> to
> place the material into the global context to refer to it.
> 2. Provide a special XPath operator to indicate we are
referencing
> a
> hidden element, possibilities include:
> a. ?../hidden(repeats)?
> b. ?hidden(../repeats)?
> c. ?../dfdl:hidden/repeats?
> 3. Only allow hidden elements to be present in top level global
> complex
> types. These can then be included where needed. (This is the
> solution
> that Suman was pushing but I don?t fully understand it
?
> in
> particular I don?t see how it resolves the ambiguity issue.)
>
>
> I believe my preference here is 2a or 2b followed by 1.
>
> Comments/suggestions/opinions?
>
> Thanks,
>
> Martin
--
---
Robert E. McGrath, Ph.D.
National Center for Supercomputing Applications
University of Illinois, Urbana-Champaign
1205 West Clark
Urbana, Illinois 61801
(217)-333-6549
mcgrath(a)ncsa.uiuc.edu
2
1
19 Jan '06
I think (hope) that with the emerging operational semantics, that there
will not be any problems putting annotations into attributes and having
them evaluated just like an element. It is not obvious to me that they
are any different.
Martin
_____
From: Mike Beckerle [mailto:beckerle@us.ibm.com]
Sent: Thursday, January 19, 2006 12:03 PM
To: Westhead, Martin (Martin)
Cc: dfdl-wg(a)ggf.org; Suman Kalia; owner-dfdl-wg(a)ggf.org; Steve Hanson
Subject: RE: [dfdl-wg] Ambiguous XPaths to hidden elements
I think we did not agree formally to this. It was one of those things
where we're trying to find something we can cut out with low risk of
later complications.
Mike Beckerle
STSM, Architect, Scalable Computing
IBM Software Group
Information Integration Solutions
Westborough, MA 01581
voice and FAX 508-599-7148
home/mobile office 508-915-4767
"Westhead, Martin (Martin)" <westhead(a)avaya.com>
Sent by: owner-dfdl-wg(a)ggf.org
01/19/2006 01:59 PM
To
"Suman Kalia" <kalia(a)ca.ibm.com>, "Steve Hanson" <smh(a)uk.ibm.com>
cc
Mike Beckerle/Worcester/IBM@IBMUS, <dfdl-wg(a)ggf.org>,
<owner-dfdl-wg(a)ggf.org>
Subject
RE: [dfdl-wg] Ambiguous XPaths to hidden elements
Why are we not allowing attributes?
Martin
_____
From: owner-dfdl-wg(a)ggf.org [mailto:owner-dfdl-wg@ggf.org] On Behalf Of
Suman Kalia
Sent: Thursday, January 19, 2006 10:57 AM
To: Steve Hanson
Cc: Mike Beckerle; dfdl-wg(a)ggf.org; owner-dfdl-wg(a)ggf.org
Subject: Fw: [dfdl-wg] Ambiguous XPaths to hidden elements
The main problem will be performance and excessively long validation
times and either asking the user to change their schema or model it
different way. These are all undesirable. Attributes I hope will be
supported in the future release . Redefine construct is hardly used in
the practical applications; at least I haven't come across any customer
that uses this construct ..
Suman Kalia
IBM Toronto Lab
WebSphere Business Integration Application Connectivity Tools
Tel : 905-413-3923 T/L 969-3923
Fax : 905-413-4850
Internet ID : kalia(a)ca.ibm.com
----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 01:49 PM -----
Steve Hanson <smh(a)uk.ibm.com>
01/19/2006 01:15 PM
To
Suman Kalia/Toronto/IBM@IBMCA
cc
Mike Beckerle <beckerle(a)us.ibm.com>, dfdl-wg(a)ggf.org,
owner-dfdl-wg(a)ggf.org
Subject
Re: Fw: [dfdl-wg] Ambiguous XPaths to hidden elements
We are already putting constraints on user-defined schema, by saying
that
we don't support redefines and attributes for example. I don't see an
issue
with further constraints if they make DFDL easier to understand and/or
easier to create a DFDL parser.
I don't have a problem with saying that an XPath must return a single
unambiguous node else it is an error.
I don't have a problem with saying the XPaths can't reference hidden
elements, and that context must be used instead.
Regards, Steve
Steve Hanson
WebSphere Message Brokers,
IBM Hursley, England
Internet: smh(a)uk.ibm.com
Phone (+44)/(0) 1962-815848
Suman Kalia
<kalia(a)ca.ibm.com
> To
Sent by: Mike Beckerle <beckerle(a)us.ibm.com>
owner-dfdl-wg@ggf cc
.org dfdl-wg(a)ggf.org,
owner-dfdl-wg(a)ggf.org
Subject
19/01/2006 18:02 Fw: [dfdl-wg] Ambiguous XPaths to
hidden elements
Well if we go with global complex type approach (which I described
option 1
in previous append) then it is not issue.. XPATH work and there are no
conflicts with user defined schemas ..
Suman Kalia
IBM Toronto Lab
WebSphere Business Integration Application Connectivity Tools
Tel : 905-413-3923 T/L 969-3923
Fax : 905-413-4850
Internet ID : kalia(a)ca.ibm.com
----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 12:59 PM -----
Mike
Beckerle/Worcester/IBM@IBMUS
To
01/19/2006 12:59 PM Suman Kalia/Toronto/IBM@IBMCA
cc
dfdl-wg(a)ggf.org,
owner-dfdl-wg(a)ggf.org
Subject
Re: Fw: [dfdl-wg] Ambiguous
XPaths to hidden elementsLink
So we have a quandry here:
on one hand we don't want to change the XPath syntax to include a device
that would let us be clear that we're navigating a hidden layer
on the other hand we don't want to constrain what can be included so
that
we wouldn't need such a device.
...mikeb
Mike Beckerle
STSM, Architect, Scalable Computing
IBM Software Group
Information Integration Solutions
Westborough, MA 01581
voice and FAX 508-599-7148
home/mobile office 508-915-4767
Suman Kalia/Toronto/IBM@IBMCA
01/19/2006 11:52 AM
To
Mike
Beckerle/Worcester/IBM@IBMUS
cc
dfdl-wg(a)ggf.org,
owner-dfdl-wg(a)ggf.org
Subject
Fw: [dfdl-wg] Ambiguous
XPaths to hidden elements
As a design point , We should strive not to put limitations on the user
defined schemas - it just works out better in the long run.
Note the xsd:groups can be nested and they could be many levels deep and
this problem is not restricted to groups included from noTarget
namespace
, it could be from any namespace. As per schema rules, all local
elements
defined in groups or complex types belong to noTarget namespace unless
elementFormDefault is explicitly set to "qualified" at schema level or
on
the specific element.
Detecting such conflicts could be quite expensive particularly when you
have very large schemas. Industry standard ACORD messaging schema is a
good example it is about 1.5 M and it takes awfully long (hours) to
validate it. Putting additional constraints like this will further slow
down validation.
Suman Kalia
IBM Toronto Lab
WebSphere Business Integration Application Connectivity Tools
Tel : 905-413-3923 T/L 969-3923
Fax : 905-413-4850
Internet ID : kalia(a)ca.ibm.com
----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 11:39 AM -----
Mike Beckerle
<beckerle(a)us.ibm.com>
Sent by: owner-dfdl-wg(a)ggf.org
To
"Robert E. McGrath"
01/19/2006 10:48 AM <mcgrath(a)ncsa.uiuc.edu>
cc
dfdl-wg(a)ggf.org,
owner-dfdl-wg(a)ggf.org
Subject
Re: Fw: [dfdl-wg] Ambiguous
XPaths to hidden elements
One idea that hasn't been advanced yet is ruling out the problematic
case.
Let me illustrate. Here's the example, modified to have a model group
reference which can introduce the name conflict:
<xs:element name="root">
<xs:complexType>
<xs:sequence>
<xs:annotation><xs:appinfo
source="http://dataformat.org" />
<hidden>
<xs:element name="repeats" type="xs:integer"/>
</hidden>
</xs:appinfo></xs:annotation
>
<xs:element name="testElement"
type="xs:integer " minOccurs="0" maxOccurs="unbounded"
dfdl:repeatCount="../repeats">
<xs:group ref="groupFromOtherSchemaFile"/>
<!-- what if this has an element decl named "repeats"? -->
</xs:complexType>
</xs:element>
So, what hasn't been suggested yet is this: What if we just say DFDL
doesn't allow this? It's an error which must be detected. This DFDL
schema
is broken because the path "../repeats" cannot be analyzed along with
the
DFDL schema to return only a single node.
I beleive name conflicts like this are what namespace management is for.
XSD has truly great namespace managment. You can solve the problem that
way.
Furthermore, when you define a reusable named group like the definer of
the
"groupFromOtherSchemaFile" above, and you put it in no target namespace,
that's the situation where this conflict can arise. Expecting that your
names are never going to conflict with anything in that case is just
naive.
It's equivalent to having global variables in a C program module and
expecting you can never link it to something else that uses the same
names.
Those name conflicts can occur, and someone has to change the
conflicting
name. In XSD we can do that by including the group in a schema which
puts
it into a target namespace so that after that the namespaces can be used
to
disambiguate.
The approach above is consistent with the path "../repeats" still being
officialy an "XPath", it just adds the semantic restriction that it must
be
an XPath that identifies a single node unambiguously, independent of
what
data is being processed. This is one of these "data independent" notions
(what I had previously been calling "static"), as we discussed
yesterday.
...mikeb
"Robert E. McGrath"
<mcgrath(a)ncsa.uiuc.edu>
Sent by: owner-dfdl-wg(a)ggf.org
To
dfdl-wg(a)ggf.org
01/19/2006 10:00 AM
cc
Subject
Re: Fw: [dfdl-wg]
Ambiguous XPaths to hidden
elements
I would want to change XPath only as a last resort. (Any of the
options is OK by me, assuming we have to mess with the Xpath
at all.)
Can we deal with this some other way?
Can we document the problematic cases, and suggest best practices that
will minimize the problem?
On Thursday 19 January 2006 08:45, Suman Kalia wrote:
> I fully agree with Steve - let's not invent another XPATH like syntax
..
>
> Suman Kalia
> IBM Toronto Lab
> WebSphere Business Integration Application Connectivity Tools
> Tel : 905-413-3923 T/L 969-3923
> Fax : 905-413-4850
> Internet ID : kalia(a)ca.ibm.com
> ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 09:43 AM
-----
>
> Steve Hanson <smh(a)uk.ibm.com>
> Sent by: owner-dfdl-wg(a)ggf.org
> 01/19/2006 04:43 AM
>
> To
> "Westhead, Martin (Martin)" <westhead(a)avaya.com>
> cc
> dfdl-wg(a)ggf.org, owner-dfdl-wg(a)ggf.org
> Subject
> Re: [dfdl-wg] Ambiguous XPaths to hidden elements
>
>
>
>
>
>
> As a DFDL parser implementor I do not want modifications to the XPath
> syntax. I want to be able to reuse existing XPath implementations.
It's
> also something else for the user to have to learn. So 2a/b/c are not
> attractive.
>
> Regards, Steve
>
> Steve Hanson
> WebSphere Message Brokers,
> IBM Hursley, England
> Internet: smh(a)uk.ibm.com
> Phone (+44)/(0) 1962-815848
>
>
>
> "Westhead, Martin
> (Martin)"
> <westhead(a)avaya.c
To
>
> om> <dfdl-wg(a)ggf.org>
> Sent by:
cc
>
> owner-dfdl-wg@ggf
> .org
Subject
>
> [dfdl-wg] Ambiguous XPaths to
> hidden elements
> 18/01/2006 20:24
>
>
>
>
>
>
>
>
>
> Hi folks,
>
> This is to try to pick up on the issue identified by Suman in today?s
> call.
>
> The Issue
> Consider the following example:
>
> <xs:element name="root">
> <xs:complexType>
> <xs:sequence>
>
<xs:annotation><xs:appinfo
> source=?http://dataformat.org? />
> <hidden>
> <xs:element name="repeats" type="xs:integer"/>
>
</hidden>
>
> </xs:appinfo></xs:annotation >
> <xs:element name="testElement"
> type="xs:integer " minOccurs=?0? maxOccurs=?unbounded?
> dfdl:repeatCount=?../repeats?>
> </xs:complexType>
> </xs:element>
>
> The problem is that the path ?../repeats? can be broken by
modifications
> to
> the logical model due to name clashes on ?repeats? and there are cases
> that
> can be constructed where this would not be obvious to a user.
>
> Possible Solutions
> Possible fixes to this include:
> 1. Disallow XPath references to hidden elements the user is
forced
> to
> place the material into the global context to refer to it.
> 2. Provide a special XPath operator to indicate we are
referencing
> a
> hidden element, possibilities include:
> a. ?../hidden(repeats)?
> b. ?hidden(../repeats)?
> c. ?../dfdl:hidden/repeats?
> 3. Only allow hidden elements to be present in top level global
> complex
> types. These can then be included where needed. (This is the
> solution
> that Suman was pushing but I don?t fully understand it
?
> in
> particular I don?t see how it resolves the ambiguity issue.)
>
>
> I believe my preference here is 2a or 2b followed by 1.
>
> Comments/suggestions/opinions?
>
> Thanks,
>
> Martin
--
---
Robert E. McGrath, Ph.D.
National Center for Supercomputing Applications
University of Illinois, Urbana-Champaign
1205 West Clark
Urbana, Illinois 61801
(217)-333-6549
mcgrath(a)ncsa.uiuc.edu
1
0
19 Jan '06
Why are we not allowing attributes?
Martin
_____
From: owner-dfdl-wg(a)ggf.org [mailto:owner-dfdl-wg@ggf.org] On Behalf Of
Suman Kalia
Sent: Thursday, January 19, 2006 10:57 AM
To: Steve Hanson
Cc: Mike Beckerle; dfdl-wg(a)ggf.org; owner-dfdl-wg(a)ggf.org
Subject: Fw: [dfdl-wg] Ambiguous XPaths to hidden elements
The main problem will be performance and excessively long validation
times and either asking the user to change their schema or model it
different way. These are all undesirable. Attributes I hope will be
supported in the future release . Redefine construct is hardly used in
the practical applications; at least I haven't come across any customer
that uses this construct ..
Suman Kalia
IBM Toronto Lab
WebSphere Business Integration Application Connectivity Tools
Tel : 905-413-3923 T/L 969-3923
Fax : 905-413-4850
Internet ID : kalia(a)ca.ibm.com
----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 01:49 PM -----
Steve Hanson <smh(a)uk.ibm.com>
01/19/2006 01:15 PM
To
Suman Kalia/Toronto/IBM@IBMCA
cc
Mike Beckerle <beckerle(a)us.ibm.com>, dfdl-wg(a)ggf.org,
owner-dfdl-wg(a)ggf.org
Subject
Re: Fw: [dfdl-wg] Ambiguous XPaths to hidden elements
We are already putting constraints on user-defined schema, by saying
that
we don't support redefines and attributes for example. I don't see an
issue
with further constraints if they make DFDL easier to understand and/or
easier to create a DFDL parser.
I don't have a problem with saying that an XPath must return a single
unambiguous node else it is an error.
I don't have a problem with saying the XPaths can't reference hidden
elements, and that context must be used instead.
Regards, Steve
Steve Hanson
WebSphere Message Brokers,
IBM Hursley, England
Internet: smh(a)uk.ibm.com
Phone (+44)/(0) 1962-815848
Suman Kalia
<kalia(a)ca.ibm.com
>
To
Sent by: Mike Beckerle
<beckerle(a)us.ibm.com>
owner-dfdl-wg@ggf
cc
.org dfdl-wg(a)ggf.org,
owner-dfdl-wg(a)ggf.org
Subject
19/01/2006 18:02 Fw: [dfdl-wg] Ambiguous XPaths to
hidden elements
Well if we go with global complex type approach (which I described
option 1
in previous append) then it is not issue.. XPATH work and there are no
conflicts with user defined schemas ..
Suman Kalia
IBM Toronto Lab
WebSphere Business Integration Application Connectivity Tools
Tel : 905-413-3923 T/L 969-3923
Fax : 905-413-4850
Internet ID : kalia(a)ca.ibm.com
----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 12:59 PM -----
Mike
Beckerle/Worcester/IBM@IBMUS
To
01/19/2006 12:59 PM Suman Kalia/Toronto/IBM@IBMCA
cc
dfdl-wg(a)ggf.org,
owner-dfdl-wg(a)ggf.org
Subject
Re: Fw: [dfdl-wg] Ambiguous
XPaths to hidden elementsLink
So we have a quandry here:
on one hand we don't want to change the XPath syntax to include a device
that would let us be clear that we're navigating a hidden layer
on the other hand we don't want to constrain what can be included so
that
we wouldn't need such a device.
...mikeb
Mike Beckerle
STSM, Architect, Scalable Computing
IBM Software Group
Information Integration Solutions
Westborough, MA 01581
voice and FAX 508-599-7148
home/mobile office 508-915-4767
Suman Kalia/Toronto/IBM@IBMCA
01/19/2006 11:52 AM
To
Mike
Beckerle/Worcester/IBM@IBMUS
cc
dfdl-wg(a)ggf.org,
owner-dfdl-wg(a)ggf.org
Subject
Fw: [dfdl-wg] Ambiguous
XPaths to hidden elements
As a design point , We should strive not to put limitations on the user
defined schemas - it just works out better in the long run.
Note the xsd:groups can be nested and they could be many levels deep and
this problem is not restricted to groups included from noTarget
namespace
, it could be from any namespace. As per schema rules, all local
elements
defined in groups or complex types belong to noTarget namespace unless
elementFormDefault is explicitly set to "qualified" at schema level or
on
the specific element.
Detecting such conflicts could be quite expensive particularly when you
have very large schemas. Industry standard ACORD messaging schema is a
good example it is about 1.5 M and it takes awfully long (hours) to
validate it. Putting additional constraints like this will further slow
down validation.
Suman Kalia
IBM Toronto Lab
WebSphere Business Integration Application Connectivity Tools
Tel : 905-413-3923 T/L 969-3923
Fax : 905-413-4850
Internet ID : kalia(a)ca.ibm.com
----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 11:39 AM -----
Mike Beckerle
<beckerle(a)us.ibm.com>
Sent by: owner-dfdl-wg(a)ggf.org
To
"Robert E. McGrath"
01/19/2006 10:48 AM <mcgrath(a)ncsa.uiuc.edu>
cc
dfdl-wg(a)ggf.org,
owner-dfdl-wg(a)ggf.org
Subject
Re: Fw: [dfdl-wg] Ambiguous
XPaths to hidden elements
One idea that hasn't been advanced yet is ruling out the problematic
case.
Let me illustrate. Here's the example, modified to have a model group
reference which can introduce the name conflict:
<xs:element name="root">
<xs:complexType>
<xs:sequence>
<xs:annotation><xs:appinfo
source="http://dataformat.org" />
<hidden>
<xs:element name="repeats" type="xs:integer"/>
</hidden>
</xs:appinfo></xs:annotation
>
<xs:element name="testElement"
type="xs:integer " minOccurs="0" maxOccurs="unbounded"
dfdl:repeatCount="../repeats">
<xs:group ref="groupFromOtherSchemaFile"/>
<!-- what if this has an element decl named "repeats"? -->
</xs:complexType>
</xs:element>
So, what hasn't been suggested yet is this: What if we just say DFDL
doesn't allow this? It's an error which must be detected. This DFDL
schema
is broken because the path "../repeats" cannot be analyzed along with
the
DFDL schema to return only a single node.
I beleive name conflicts like this are what namespace management is for.
XSD has truly great namespace managment. You can solve the problem that
way.
Furthermore, when you define a reusable named group like the definer of
the
"groupFromOtherSchemaFile" above, and you put it in no target namespace,
that's the situation where this conflict can arise. Expecting that your
names are never going to conflict with anything in that case is just
naive.
It's equivalent to having global variables in a C program module and
expecting you can never link it to something else that uses the same
names.
Those name conflicts can occur, and someone has to change the
conflicting
name. In XSD we can do that by including the group in a schema which
puts
it into a target namespace so that after that the namespaces can be used
to
disambiguate.
The approach above is consistent with the path "../repeats" still being
officialy an "XPath", it just adds the semantic restriction that it must
be
an XPath that identifies a single node unambiguously, independent of
what
data is being processed. This is one of these "data independent" notions
(what I had previously been calling "static"), as we discussed
yesterday.
...mikeb
"Robert E. McGrath"
<mcgrath(a)ncsa.uiuc.edu>
Sent by: owner-dfdl-wg(a)ggf.org
To
dfdl-wg(a)ggf.org
01/19/2006 10:00 AM
cc
Subject
Re: Fw: [dfdl-wg]
Ambiguous XPaths to
hidden
elements
I would want to change XPath only as a last resort. (Any of the
options is OK by me, assuming we have to mess with the Xpath
at all.)
Can we deal with this some other way?
Can we document the problematic cases, and suggest best practices that
will minimize the problem?
On Thursday 19 January 2006 08:45, Suman Kalia wrote:
> I fully agree with Steve - let's not invent another XPATH like syntax
..
>
> Suman Kalia
> IBM Toronto Lab
> WebSphere Business Integration Application Connectivity Tools
> Tel : 905-413-3923 T/L 969-3923
> Fax : 905-413-4850
> Internet ID : kalia(a)ca.ibm.com
> ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 09:43 AM
-----
>
> Steve Hanson <smh(a)uk.ibm.com>
> Sent by: owner-dfdl-wg(a)ggf.org
> 01/19/2006 04:43 AM
>
> To
> "Westhead, Martin (Martin)" <westhead(a)avaya.com>
> cc
> dfdl-wg(a)ggf.org, owner-dfdl-wg(a)ggf.org
> Subject
> Re: [dfdl-wg] Ambiguous XPaths to hidden elements
>
>
>
>
>
>
> As a DFDL parser implementor I do not want modifications to the XPath
> syntax. I want to be able to reuse existing XPath implementations.
It's
> also something else for the user to have to learn. So 2a/b/c are not
> attractive.
>
> Regards, Steve
>
> Steve Hanson
> WebSphere Message Brokers,
> IBM Hursley, England
> Internet: smh(a)uk.ibm.com
> Phone (+44)/(0) 1962-815848
>
>
>
> "Westhead, Martin
> (Martin)"
> <westhead(a)avaya.c
To
>
> om> <dfdl-wg(a)ggf.org>
> Sent by:
cc
>
> owner-dfdl-wg@ggf
> .org
Subject
>
> [dfdl-wg] Ambiguous XPaths to
> hidden elements
> 18/01/2006 20:24
>
>
>
>
>
>
>
>
>
> Hi folks,
>
> This is to try to pick up on the issue identified by Suman in today?s
> call.
>
> The Issue
> Consider the following example:
>
> <xs:element name="root">
> <xs:complexType>
> <xs:sequence>
>
<xs:annotation><xs:appinfo
> source=?http://dataformat.org? />
> <hidden>
> <xs:element name="repeats" type="xs:integer"/>
>
</hidden>
>
> </xs:appinfo></xs:annotation >
> <xs:element name="testElement"
> type="xs:integer " minOccurs=?0? maxOccurs=?unbounded?
> dfdl:repeatCount=?../repeats?>
> </xs:complexType>
> </xs:element>
>
> The problem is that the path ?../repeats? can be broken by
modifications
> to
> the logical model due to name clashes on ?repeats? and there are cases
> that
> can be constructed where this would not be obvious to a user.
>
> Possible Solutions
> Possible fixes to this include:
> 1. Disallow XPath references to hidden elements the user is
forced
> to
> place the material into the global context to refer to it.
> 2. Provide a special XPath operator to indicate we are
referencing
> a
> hidden element, possibilities include:
> a. ?../hidden(repeats)?
> b. ?hidden(../repeats)?
> c. ?../dfdl:hidden/repeats?
> 3. Only allow hidden elements to be present in top level global
> complex
> types. These can then be included where needed. (This is the
> solution
> that Suman was pushing but I don?t fully understand it
?
> in
> particular I don?t see how it resolves the ambiguity issue.)
>
>
> I believe my preference here is 2a or 2b followed by 1.
>
> Comments/suggestions/opinions?
>
> Thanks,
>
> Martin
--
---
Robert E. McGrath, Ph.D.
National Center for Supercomputing Applications
University of Illinois, Urbana-Champaign
1205 West Clark
Urbana, Illinois 61801
(217)-333-6549
mcgrath(a)ncsa.uiuc.edu
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