[dfdl-wg] Ambiguous XPaths to hidden elements

[Steve Hanson]

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)"                                                     
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                                       [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