(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 >-----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 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@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 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@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"/> >> </hidden> >> </xs:appinfo></xs:annotation >> >> <xs:element name="testElement" >> type="xs:integer " minOccurs=?0? maxOccurs=?unbounded? >> dfdl:repeatCount=?../repeats?> >> >> <xs:group ref="groupFromOtherSchemaFile"/> >>  >> >> </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@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