Fw: [dfdl-wg] Ambiguous XPaths to hidden elements

[Robert E. McGrath]

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