-----Original Message----- From: owner-dfdl-wg@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@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
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
applications; at least I haven't come across any customer that uses
(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@avaya.com> 01/19/2006 02:20 PM To "Robert E. McGrath" <mcgrath@ncsa.uiuc.edu>, "Suman Kalia" <kalia@ca.ibm.com>, "Steve Hanson" <smh@uk.ibm.com> cc Mike Beckerle/Worcester/IBM@IBMUS, <dfdl-wg@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 based practical 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@ca.ibm.com ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 01:49 PM
Steve Hanson <smh@uk.ibm.com> 01/19/2006 01:15 PM
To Suman Kalia/Toronto/IBM@IBMCA cc Mike Beckerle <beckerle@us.ibm.com>, dfdl-wg@ggf.org, owner-dfdl-wg@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@uk.ibm.com Phone (+44)/(0) 1962-815848
Suman Kalia <kalia@ca.ibm.com
> To
Sent by: Mike Beckerle <beckerle@us.ibm.com>
owner-dfdl-wg@ggf cc
.org dfdl-wg@ggf.org, owner-dfdl-wg@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@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@ggf.org, owner-dfdl-wg@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
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
device 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@ggf.org, owner-dfdl-wg@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@ca.ibm.com ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 11:39 AM
Mike Beckerle <beckerle@us.ibm.com> Sent by: owner-dfdl-wg@ggf.org
To
"Robert E. McGrath" 01/19/2006 10:48 AM <mcgrath@ncsa.uiuc.edu>
cc
dfdl-wg@ggf.org, owner-dfdl-wg@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"/>
</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
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
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
</hidden> the that 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@ncsa.uiuc.edu> Sent by: owner-dfdl-wg@ggf.org
To
dfdl-wg@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@ca.ibm.com ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 09:43 AM
Steve Hanson <smh@uk.ibm.com> Sent by: owner-dfdl-wg@ggf.org 01/19/2006 04:43 AM
To "Westhead, Martin (Martin)" <westhead@avaya.com> cc dfdl-wg@ggf.org, owner-dfdl-wg@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@uk.ibm.com Phone (+44)/(0) 1962-815848
"Westhead, Martin (Martin)" <westhead@avaya.c
To
om> <dfdl-wg@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@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@ncsa.uiuc.edu