January 2006 - dfdl-wg - lists.ogf.org

Fw: [dfdl-wg] Ambiguous XPaths to hidden elements
by Suman Kalia 19 Jan '06

19 Jan '06

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(a)ca.ibm.com ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 11:39 AM ----- Mike Beckerle <beckerle(a)us.ibm.com> Sent by: owner-dfdl-wg(a)ggf.org 01/19/2006 10:48 AM To "Robert E. McGrath" <mcgrath(a)ncsa.uiuc.edu> cc dfdl-wg(a)ggf.org, owner-dfdl-wg(a)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(a)ncsa.uiuc.edu> Sent by: owner-dfdl-wg(a)ggf.org 01/19/2006 10:00 AM To dfdl-wg(a)ggf.org 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(a)ca.ibm.com > ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 09:43 AM ----- > > Steve Hanson <smh(a)uk.ibm.com> > Sent by: owner-dfdl-wg(a)ggf.org > 01/19/2006 04:43 AM > > To > "Westhead, Martin (Martin)" <westhead(a)avaya.com> > cc > dfdl-wg(a)ggf.org, owner-dfdl-wg(a)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(a)uk.ibm.com > Phone (+44)/(0) 1962-815848 > > > > "Westhead, Martin > (Martin)" > <westhead(a)avaya.c To > > om> <dfdl-wg(a)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(a)ncsa.uiuc.edu

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RE: Fw: [dfdl-wg] Ambiguous XPaths to hidden elements
by Westhead, Martin (Martin) 19 Jan '06

19 Jan '06

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(a)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(a)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(a)ca.ibm.com >> ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 01:49 PM ----- >> >> Steve Hanson <smh(a)uk.ibm.com> >> 01/19/2006 01:15 PM >> >> To >> Suman Kalia/Toronto/IBM@IBMCA >> cc >> Mike Beckerle <beckerle(a)us.ibm.com>, dfdl-wg(a)ggf.org, >> owner-dfdl-wg(a)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(a)uk.ibm.com >> Phone (+44)/(0) 1962-815848 >> >> >> >> Suman Kalia >> <kalia(a)ca.ibm.com >> >> > >To >> >> Sent by: Mike Beckerle ><beckerle(a)us.ibm.com> >> >> owner-dfdl-wg@ggf >cc >> >> .org dfdl-wg(a)ggf.org, >> owner-dfdl-wg(a)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(a)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(a)ggf.org, >> owner-dfdl-wg(a)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(a)ggf.org, >> owner-dfdl-wg(a)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(a)ca.ibm.com >> ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 11:39 AM ----- >> >> Mike Beckerle >> <beckerle(a)us.ibm.com> >> Sent by: owner-dfdl-wg(a)ggf.org >> >To >> >> "Robert E. McGrath" >> 01/19/2006 10:48 AM <mcgrath(a)ncsa.uiuc.edu> >> >cc >> >> dfdl-wg(a)ggf.org, >> owner-dfdl-wg(a)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(a)ncsa.uiuc.edu> >> Sent by: owner-dfdl-wg(a)ggf.org >> >To >> >> dfdl-wg(a)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(a)ca.ibm.com >> > ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 09:43 AM ----- >> > >> > Steve Hanson <smh(a)uk.ibm.com> >> > Sent by: owner-dfdl-wg(a)ggf.org >> > 01/19/2006 04:43 AM >> > >> > To >> > "Westhead, Martin (Martin)" <westhead(a)avaya.com> >> > cc >> > dfdl-wg(a)ggf.org, owner-dfdl-wg(a)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(a)uk.ibm.com >> > Phone (+44)/(0) 1962-815848 >> > >> > >> > >> > "Westhead, Martin >> > (Martin)" >> > <westhead(a)avaya.c >> >> To >> >> > om> <dfdl-wg(a)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(a)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(a)ncsa.uiuc.edu

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Fw: [dfdl-wg] Ambiguous XPaths to hidden elements
by Suman Kalia 19 Jan '06

19 Jan '06

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(a)ca.ibm.com ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 01:49 PM ----- Steve Hanson <smh(a)uk.ibm.com> 01/19/2006 01:15 PM To Suman Kalia/Toronto/IBM@IBMCA cc Mike Beckerle <beckerle(a)us.ibm.com>, dfdl-wg(a)ggf.org, owner-dfdl-wg(a)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(a)uk.ibm.com Phone (+44)/(0) 1962-815848 Suman Kalia <kalia(a)ca.ibm.com > To Sent by: Mike Beckerle <beckerle(a)us.ibm.com> owner-dfdl-wg@ggf cc .org dfdl-wg(a)ggf.org, owner-dfdl-wg(a)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(a)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(a)ggf.org, owner-dfdl-wg(a)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(a)ggf.org, owner-dfdl-wg(a)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(a)ca.ibm.com ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 11:39 AM ----- Mike Beckerle <beckerle(a)us.ibm.com> Sent by: owner-dfdl-wg(a)ggf.org To "Robert E. McGrath" 01/19/2006 10:48 AM <mcgrath(a)ncsa.uiuc.edu> cc dfdl-wg(a)ggf.org, owner-dfdl-wg(a)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(a)ncsa.uiuc.edu> Sent by: owner-dfdl-wg(a)ggf.org To dfdl-wg(a)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(a)ca.ibm.com > ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 09:43 AM ----- > > Steve Hanson <smh(a)uk.ibm.com> > Sent by: owner-dfdl-wg(a)ggf.org > 01/19/2006 04:43 AM > > To > "Westhead, Martin (Martin)" <westhead(a)avaya.com> > cc > dfdl-wg(a)ggf.org, owner-dfdl-wg(a)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(a)uk.ibm.com > Phone (+44)/(0) 1962-815848 > > > > "Westhead, Martin > (Martin)" > <westhead(a)avaya.c To > > om> <dfdl-wg(a)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(a)ncsa.uiuc.edu

2 1

Fw: [dfdl-wg] Ambiguous XPaths to hidden elements
by Suman Kalia 19 Jan '06

19 Jan '06

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(a)ca.ibm.com ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 09:43 AM ----- Steve Hanson <smh(a)uk.ibm.com> Sent by: owner-dfdl-wg(a)ggf.org 01/19/2006 04:43 AM To "Westhead, Martin (Martin)" <westhead(a)avaya.com> cc dfdl-wg(a)ggf.org, owner-dfdl-wg(a)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(a)uk.ibm.com Phone (+44)/(0) 1962-815848 "Westhead, Martin (Martin)" <westhead(a)avaya.c To om> <dfdl-wg(a)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

4 4

Fw: [dfdl-wg] Ambiguous XPaths to hidden elements
by Suman Kalia 19 Jan '06

19 Jan '06

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(a)ca.ibm.com ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 12:59 PM ----- Mike Beckerle/Worcester/IBM@IBMUS 01/19/2006 12:59 PM To Suman Kalia/Toronto/IBM@IBMCA cc dfdl-wg(a)ggf.org, owner-dfdl-wg(a)ggf.org Subject Re: Fw: [dfdl-wg] Ambiguous XPaths to hidden elements 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(a)ggf.org, owner-dfdl-wg(a)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(a)ca.ibm.com ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 11:39 AM ----- Mike Beckerle <beckerle(a)us.ibm.com> Sent by: owner-dfdl-wg(a)ggf.org 01/19/2006 10:48 AM To "Robert E. McGrath" <mcgrath(a)ncsa.uiuc.edu> cc dfdl-wg(a)ggf.org, owner-dfdl-wg(a)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(a)ncsa.uiuc.edu> Sent by: owner-dfdl-wg(a)ggf.org 01/19/2006 10:00 AM To dfdl-wg(a)ggf.org 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(a)ca.ibm.com > ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 09:43 AM ----- > > Steve Hanson <smh(a)uk.ibm.com> > Sent by: owner-dfdl-wg(a)ggf.org > 01/19/2006 04:43 AM > > To > "Westhead, Martin (Martin)" <westhead(a)avaya.com> > cc > dfdl-wg(a)ggf.org, owner-dfdl-wg(a)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(a)uk.ibm.com > Phone (+44)/(0) 1962-815848 > > > > "Westhead, Martin > (Martin)" > <westhead(a)avaya.c To > > om> <dfdl-wg(a)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(a)ncsa.uiuc.edu

2 1

Re: Fw: [dfdl-wg] Ambiguous XPaths to hidden elements
by Mike Beckerle 19 Jan '06

19 Jan '06

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(a)ggf.org, owner-dfdl-wg(a)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(a)ca.ibm.com ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 11:39 AM ----- Mike Beckerle <beckerle(a)us.ibm.com> Sent by: owner-dfdl-wg(a)ggf.org 01/19/2006 10:48 AM To "Robert E. McGrath" <mcgrath(a)ncsa.uiuc.edu> cc dfdl-wg(a)ggf.org, owner-dfdl-wg(a)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(a)ncsa.uiuc.edu> Sent by: owner-dfdl-wg(a)ggf.org 01/19/2006 10:00 AM To dfdl-wg(a)ggf.org 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(a)ca.ibm.com > ----- Forwarded by Suman Kalia/Toronto/IBM on 01/19/2006 09:43 AM ----- > > Steve Hanson <smh(a)uk.ibm.com> > Sent by: owner-dfdl-wg(a)ggf.org > 01/19/2006 04:43 AM > > To > "Westhead, Martin (Martin)" <westhead(a)avaya.com> > cc > dfdl-wg(a)ggf.org, owner-dfdl-wg(a)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(a)uk.ibm.com > Phone (+44)/(0) 1962-815848 > > > > "Westhead, Martin > (Martin)" > <westhead(a)avaya.c To > > om> <dfdl-wg(a)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(a)ncsa.uiuc.edu

1 0

RE: [dfdl-wg] Ambiguous XPaths to hidden elements
by Westhead, Martin (Martin) 19 Jan '06

19 Jan '06

Hi All, I believe the XPath standard permits the extension of the language by the addition of new functions. If I'm correct 1 and 2 are not a change to the language but are (I believe) a permitted extension. However I would be happy with 1. It is probably tidier and as Steve points out (later) it seems to be suggestive of a simple implementation. Martin >-----Original Message----- >From: owner-dfdl-wg(a)ggf.org [mailto:owner-dfdl-wg@ggf.org] On Behalf Of >Steve Hanson >Sent: Thursday, January 19, 2006 1:44 AM >To: Westhead, Martin (Martin) >Cc: dfdl-wg(a)ggf.org; owner-dfdl-wg(a)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(a)uk.ibm.com >Phone (+44)/(0) 1962-815848 > > > > "Westhead, Martin > (Martin)" > <westhead(a)avaya.c To > om> <dfdl-wg(a)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

1 0

Fw: [dfdl-wg] Ambiguous XPaths to hidden elements
by Steve Hanson 19 Jan '06

19 Jan '06

I think there is a wider issue here that we need to consider before we can answer this question, and that is what do we plan to say in the DFDL standard about the output we create? Let me explain this further. In IBM we have several different products that could exploit a DFDL parser, but these products all have a different way of exposing the output to the user, normally some kind of DOM-like tree model with an accompanying API. This is almost certainly the case elsewhere too because there is no equivalent standard to DOM for non-XML data. A DFDL parser must therefore provide a SAX-like interface and generate events, leaving it up to the caller to create the tree model (even if it also provided the capability to build an XML DOM model). However both the use of XPath during the parse and hidden elements pose problems for a DFDL parser. - All the XPath implementations I have encountered are bound to the type of tree that is being created - DOM or SDO or WMB for example. With SAX there is no standard tree. - Hidden elements will not by definition appear in a DOM tree. So even in DOM mode a DFDL parser needs some internal mechanism for retaining parsed values that could be referenced by XPath, and its XPath implemetation must therefore use this mechanism. Note it should only use this mechanism for retaining the values of those elements that it knows could be referenced by XPath, ie, it is a sparse mechanism. Otherwise the amount of memory used for large messages becomes unacceptable. An alternative is to force the caller to provide a handler that gets invoked when XPath needs to access the caller's tree (implies disallowing XPath for hidden elements). I don't think a handler approach would be acceptable, even if a DOM alternative was provided. Perhaps it is time to give some thought to the API aspect of DFDL ? (The implication above is that an existing XPath implementation can't be used as is. True, but it is only the tree/model interface that needs changing and this is an internal. I'm still not happy with 2a/b/c below which change the XPath externals. I prefer 1 below.) Regards, Steve Steve Hanson WebSphere Message Brokers, IBM Hursley, England Internet: smh(a)uk.ibm.com Phone (+44)/(0) 1962-815848 ----- Forwarded by Steve Hanson/UK/IBM on 19/01/2006 09:53 ----- Steve Hanson/UK/IBM To 19/01/2006 09:43 "Westhead, Martin (Martin)" <westhead(a)avaya.com> cc dfdl-wg(a)ggf.org, owner-dfdl-wg(a)ggf.org Subject Re: [dfdl-wg] Ambiguous XPaths to hidden elements(Document link: 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(a)uk.ibm.com Phone (+44)/(0) 1962-815848 "Westhead, Martin (Martin)" <westhead(a)avaya.c To om> <dfdl-wg(a)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

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Ambiguous XPaths to hidden elements
by Westhead, Martin (Martin) 19 Jan '06

19 Jan '06

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

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Notes from Telcon 2006-1-18
by Westhead, Martin (Martin) 18 Jan '06

18 Jan '06

Present: -------- Martin Westhead Mike Beckerle Bob McGrath Steve Hanson Geoff Judd Suman F2F --- It was agreed that we would take forward a plan to have a F2F meeting 1-3 March in Avaya at Milpitas. Final confirmation (hopefully) before next week. Reports ------- Scoping document is progressing. Hopefully we will see something soon. Context document ---------------- - Typo: Zipcode vs numberOfFields - Typo: $ in name attribute (several places) - Issues: If property is not declared with a type first time is it an error Hidden Element document ----------------------- - Issue: Ambiguity of XPath reference (changes to non-hidden portion can break the metadata reference) - Presentation: Clarify text about access to hidden elements

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