Fw: [dfdl-wg] Ambiguous XPaths to hidden elements
Westhead, Martin (Martin)
westhead at avaya.com
Thu Jan 19 13:20:26 CST 2006
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 at ggf.org [mailto:owner-dfdl-wg at 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 at 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 at ca.ibm.com
>> ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 01:49 PM
-----
>>
>> Steve Hanson <smh at uk.ibm.com>
>> 01/19/2006 01:15 PM
>>
>> To
>> Suman Kalia/Toronto/IBM at IBMCA
>> cc
>> Mike Beckerle <beckerle at us.ibm.com>, dfdl-wg at ggf.org,
>> owner-dfdl-wg at 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 at uk.ibm.com
>> Phone (+44)/(0) 1962-815848
>>
>>
>>
>> Suman Kalia
>> <kalia at ca.ibm.com
>>
>> >
>To
>>
>> Sent by: Mike Beckerle
><beckerle at us.ibm.com>
>>
>> owner-dfdl-wg at ggf
>cc
>>
>> .org dfdl-wg at ggf.org,
>> owner-dfdl-wg at 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 at ca.ibm.com
>> ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 12:59 PM
-----
>>
>> Mike
>> Beckerle/Worcester/IBM at IBMUS
>>
>>
>To
>>
>> 01/19/2006 12:59 PM Suman
Kalia/Toronto/IBM at IBMCA
>>
>cc
>>
>> dfdl-wg at ggf.org,
>> owner-dfdl-wg at 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 at IBMCA
>>
>>
>> 01/19/2006 11:52 AM
>To
>>
>> Mike
>>
Beckerle/Worcester/IBM at IBMUS
>>
>cc
>>
>> dfdl-wg at ggf.org,
>> owner-dfdl-wg at 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 at ca.ibm.com
>> ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 11:39 AM
-----
>>
>> Mike Beckerle
>> <beckerle at us.ibm.com>
>> Sent by: owner-dfdl-wg at ggf.org
>>
>To
>>
>> "Robert E. McGrath"
>> 01/19/2006 10:48 AM <mcgrath at ncsa.uiuc.edu>
>>
>cc
>>
>> dfdl-wg at ggf.org,
>> owner-dfdl-wg at 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 at ncsa.uiuc.edu>
>> Sent by: owner-dfdl-wg at ggf.org
>>
>To
>>
>> dfdl-wg at 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 at ca.ibm.com
>> > ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 09:43 AM
-----
>> >
>> > Steve Hanson <smh at uk.ibm.com>
>> > Sent by: owner-dfdl-wg at ggf.org
>> > 01/19/2006 04:43 AM
>> >
>> > To
>> > "Westhead, Martin (Martin)" <westhead at avaya.com>
>> > cc
>> > dfdl-wg at ggf.org, owner-dfdl-wg at 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 at uk.ibm.com
>> > Phone (+44)/(0) 1962-815848
>> >
>> >
>> >
>> > "Westhead, Martin
>> > (Martin)"
>> > <westhead at avaya.c
>>
>> To
>>
>> > om> <dfdl-wg at ggf.org>
>> > Sent by:
>>
>> cc
>>
>> > owner-dfdl-wg at 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 at 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 at ncsa.uiuc.edu
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