Perhaps there is a discussion here for later, but with hidden elements I don't think there's much of an issue here. My take on this is that we are using the XSD to do more than it is supposed to, we are not just using it to describe valid XML we are using it constructively to describe how to build an XML instance. We are establishing a semantics for how the DFDL parser constructs this XML document from the XSD and the data. Now, it is easy to imagine cases where you have a particular xml model you want to populate which is similar to the data but is perhaps a subset with slightly different ordering. Hidden elements make this easy to handle. You put the stuff that is to be omitted in a hidden element. Stuff that is out of order can be put in hidden elements and then referenced by correctly ordered elements for value. In this framework attributes are just another node for data population. If it happens that you can arrange the XML Schema so that the order in which attributes are laid out in the file corresponds to the ordering of the data, well then its no different from elements. If there are constraints that prevent that ordering then you are in a situation just like the one I describe above and you solve it with hidden elements. So I don't really disagree with your points below it just seems to me that there's nothing much to worry about here. I can't see why we would put it off - there's no extra work to do? Cheers, Martin _____ From: Mike Beckerle [mailto:beckerle@us.ibm.com] Sent: Thursday, January 19, 2006 12:27 PM To: Westhead, Martin (Martin) Cc: dfdl-wg@ggf.org; Suman Kalia; owner-dfdl-wg@ggf.org; Steve Hanson Subject: Re: Attributes - (was Ambiguous XPaths to hidden elements) Here's some of the issues with attributes: 1) every element can have two kinds of children now, attributes and sub-elements. Actual DFDL-described data will typically have just one kind of sub-fields of data, but some want to be mapped to attributes, others to elements. How do you specify how the attributes are separated from the elements. Do the attributes have to be first, or last, or can they be interleaved with the sub-elements' physical data? 2) in XSD syntax, if you define a element with both sub-elements and attributes, the attributes textually come after the sub-elements. This means you may or may not have them in the right order for DFDL annotation to be convenient. E.g., suppose you had 5 children the first 2 you want to be attributes the remaining 3 sub-elements in a sequence. How can you annotate this conveniently? 3)The attributes are always unordered w.r.t. the XSD concept, but the sub-elements can be either ordered or un-ordered. These all seemed like avoidable issues. That is, I'm not saying there is no good solution here, I'm just saying it's probably uninteresting. One solution to the whole issue is to say that attributes can't be in the bottom-most layer. I.e., you create them by referencing element values in hidden or non-hidden layers. This eliminates all the above problems.It is equivalent to using a stylesheet to create the attributes you want from elements-only data. However, by use of the layers you can embed it all right into the DFDL schema. I also believe attributes are to some extent beside the point for DFDL. What we needed from XSD is a standardized hierarchical type system that we can hang represetnation properties on. We get that by using the elements-only subset of XSD. Attributes are only needed if we broaden our agenda to include "creating the XML I want out of my data", which layering can do. 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 03:05 PM To Mike Beckerle/Worcester/IBM@IBMUS cc <dfdl-wg@ggf.org>, "Suman Kalia" <kalia@ca.ibm.com>, <owner-dfdl-wg@ggf.org>, "Steve Hanson" <smh@uk.ibm.com> Subject Attributes - (was Ambiguous XPaths to hidden elements) I think (hope) that with the emerging operational semantics, that there will not be any problems putting annotations into attributes and having them evaluated just like an element. It is not obvious to me that they are any different. Martin _____ From: Mike Beckerle [mailto:beckerle@us.ibm.com] Sent: Thursday, January 19, 2006 12:03 PM To: Westhead, Martin (Martin) Cc: dfdl-wg@ggf.org; Suman Kalia; owner-dfdl-wg@ggf.org; Steve Hanson Subject: RE: [dfdl-wg] Ambiguous XPaths to hidden elements I think we did not agree formally to this. It was one of those things where we're trying to find something we can cut out with low risk of later complications. 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> Sent by: owner-dfdl-wg@ggf.org 01/19/2006 01:59 PM To "Suman Kalia" <kalia@ca.ibm.com>, "Steve Hanson" <smh@uk.ibm.com> cc Mike Beckerle/Worcester/IBM@IBMUS, <dfdl-wg@ggf.org>, <owner-dfdl-wg@ggf.org> Subject RE: [dfdl-wg] Ambiguous XPaths to hidden elements Why are we not allowing attributes? Martin _____ From: owner-dfdl-wg@ggf.org [mailto:owner-dfdl-wg@ggf.org] On Behalf Of Suman Kalia Sent: Thursday, January 19, 2006 10:57 AM To: Steve Hanson Cc: Mike Beckerle; dfdl-wg@ggf.org; owner-dfdl-wg@ggf.org Subject: Fw: [dfdl-wg] Ambiguous XPaths to hidden elements 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"/> <!-- 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 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