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Subject: Re: [sdo] XML Fidelity issue: xsi:nil with attributes
Hi Frank,
xsi:schemaLocation & xsi:noNamespaceSchemaLocation are currently tracked
by commonj.sdo.helper.XMLDocument, why would these need to be technical
properties?
-Blaise
Frank Budinsky wrote:
> Hi Guys,
>
> I think something like "system properties" might be a better name than
> "technical properties". XML has 4 intrinsic system/technical properties,
> namely the 4 attributes in the xsi namespace: xsi:type, xsi:nil,
> xsi:schemaLocation, and xsi:noNamespaceSchemaLocation. These 4 are
> built-in attributes that all XML processors allow. I think we need to say
> that those 4 are system properties by default. If users want to define
> additional ones, they can do it with Ron's proposed sdo annotation (but
> note that they can result in invalid XML serializations).
>
> I'm not really crazy about adding a new API for this to SDO. Where would
> getTechnicalProperties() go? DataObject, DataHelper, or somewhere else? I
> wonder if we could require technical/system properties to map to XML
> attributes? If so, maybe we could access them using a solution we might
> come up with for SDO-132?
>
> Frank
>
>
>
>
> "James Hart" <James.Hart@roguewave.com>
> 06/19/2008 09:23 AM
>
> To
> "Barack, Ron" <ron.barack@sap.com>, Frank Budinsky/Toronto/IBM@IBMCA,
> <sdo@lists.oasis-open.org>
> cc
>
> Subject
> RE: [sdo] XML Fidelity issue: xsi:nil with attributes
>
>
>
>
>
>
> I really like this more generalized approach with "Option 2".
>
> It would also be nice if there was an additional API similar to
> getInstanceProperties() that would be PropertyList
> getTechnicalProperties(). In the long run it would even be nicer if there
> becomes a getTechnicalProperties(Namespace) api. That way a user of the
> technical properties wouldn't have to getProperty(TProp) on everything it
> may know about, but instead get a list, loop through them and see if it
> recognizes any of them.
>
> One benefit comes if there is a larger overhead in multiple calls to
> getProperty() than a single getTechnicalProperties() call. Another benefit
> is if a DAS may recognize 100 technical properties but likely there will
> only be one or two ever set on any type or data object it will save a
> large amount of time to get a list and check if it recognizes those.
>
> Thanks,
> James
>
> -----Original Message-----
> From: Barack, Ron [mailto:ron.barack@sap.com]
> Sent: Thursday, June 19, 2008 4:25 AM
> To: Frank Budinsky; sdo@lists.oasis-open.org
> Subject: AW: [sdo] XML Fidelity issue: xsi:nil with attributes
>
> Hi,
>
> I would like to propose generalizing Option 2 below as follows. We define
> an open content property
> {commonj.sdo}technicalProperty with type "boolean".
>
> When an open content property is annotated with technicalProperty="true",
> then the property may be set on any object, regardless of whether the
> object's type is open or not. This is the behavior described under
> "Option 2", except now it is not based on a pre-defined set of properties
> hardcoded into SDO, but rather on the "technicalProperty" mechanism.
>
> Technical properties DO NOT appear in an object's instance properties.
> Instance properties are typically business relevant, technical properties
> are not. Technical properties can only be retrieved or set through the
> DataObject.get(Property) or the DataObject.set(Property, Object) APIs.
>
> We must further define the open content property
> {http://www.w3.org/2001/XMLSchema-instance}nil"; and declare it to have
> technicalProperty="true".
>
> Best Regards,
> Ron
>
> -----Ursprüngliche Nachricht-----
> Von: Frank Budinsky [mailto:frankb@ca.ibm.com]
> Gesendet: Montag, 16. Juni 2008 21:02
> An: sdo@lists.oasis-open.org
> Betreff: RE: [sdo] XML Fidelity issue: xsi:nil with attributes
>
> Hi James,
>
> If I understand you, you're suggesting 1) a generic mechanism for adding
> meta information to meta information, and 2) a separate API for accessing
> instances of this meta information.
>
> For 1), I think the instanceProperty support we added to Type and Property
>
> is mostly what we need (except, I suppose, it's missing a set() API if the
>
> types are defined with XSD).
>
> For 2), I'm not sure I see the value of adding the complexity of a
> separate API for this. Simply using DataObject.get/set() seems like a very
>
> clean and simple approach to me.
>
> Frank.
>
>
>
>
> "James Hart" <James.Hart@roguewave.com>
> 06/11/2008 10:15 AM
>
> To
> "Barack, Ron" <ron.barack@sap.com>, <sdo@lists.oasis-open.org>
> cc
>
> Subject
> RE: [sdo] XML Fidelity issue: xsi:nil with attributes
>
>
>
>
>
>
> I like option two, but can we make it more generic? Could we just have a
> method on Type and Property such as
> set/getMetaProperty<val_type>(property, xmlnamespace, name, value). This
> would be an instance property but only accessable through this API and
> only should be used for auxiliary information that is critical to the data
>
> itself.
>
> In this way we could say something like any meta property can be added to
> any kind of property. By best practice it would only store meta
> information that would only be important to a DAS or a user that expects
> auxiliary information from a DAS. We could even expand that and say that
> certain projects would use these meta data to hold their own custom states
>
> and this is also how the projections can "share" information with other
> projections.
>
> So in terms of the nil property now when the XSDHelper reads in an xsd it
> could do:
> Type<bool>.addMetaProperty(nillableElementProperty, xsdnamespace,
> "nillable", true);
>
> And when the XSDHelper reads in a file where something is set, when it is
> creating the DataObject it could do something like:
> DataObject.<bool>setMetaProperty("thiselementwasnill", xsdnamespace,
> "nill", true);
>
> So now if the user wants to tell the XMLDas to marshall out something as
> nill they would:
> DataObject.<bool>setMetaProperty("thiselementwasnill", xsdnamespace,
> "nill", true);
>
> And then the XMLHelper on read just simply would check to see if the
> "nillable" meta information is on the type and if it is check to see if
> the xsd:nill meta information is set to true on the actual property where
> the elements dataObjectType is located.
>
> Now the user can use introspection on the meta properties to get meta
> information that was XML or any other medium specific meta information.
> But I think the really cool thing about this is that any kind of DAS can
> add any kind of information and now interop with compatible meta
> information from other DAS's.
>
> So I guess the solution I am proposing is a more robust system that allows
>
> for meta information that isn't XML centric but generic enough to hold any
>
> kind of meta information. One might argue since you can put instance
> properties on types that this already a way to provide meta information.
> However, there is no real way currently to provide instanced meta
> information on properties on a DataObject that has no relation to the
> stored information.
>
> Of course this is all just very preliminary in of an idea and maybe there
> are still use cases it doesn't cover well, but if this system was in place
>
> for 2.1 I think I could of implemented an XSDHelper in such a way it would
>
> of provided all the meta information needed so XMLHelper could of
> inspected a type created by the XSDHelper and generated a valid XML
> instance document, which is valuable because we have ran into a couple of
> customer use cases for that.
>
> Thanks,
> James
>
>
>
> -----Original Message-----
> From: Barack, Ron [mailto:ron.barack@sap.com]
> Sent: Wednesday, June 11, 2008 6:47 AM
> To: sdo@lists.oasis-open.org
> Subject: AW: [sdo] XML Fidelity issue: xsi:nil with attributes
>
> Hi SDO-ers,
>
> I want to bring up some additional options for dealing with xsi:nil.
>
> OPTION 1:
>
> This is more or less motivated by how JAXB deals with xsi:nil. JAXB
> defines JAXBElement, which more or less corresponds to the elements in our
>
> own beloved Sequence. JAXBElement has a property "isNil", by extension,
> we could add an "isNil(int index)" to Sequence, plus a corresponding
> setter.
>
> The implication would be that types that have elements with
> xsi:nillable="true" would be sequenced. Since there are costs associated
> with sequenced types, we might make to make this rule more precise. We
> could say, that nillable implies sequenced only if the element's type does
>
> not extend a simple type.
>
> OPTION 2:
>
> We define a set of global properties that can be set on objects whether or
>
> not object.getType().isOpen() is true. Among these global properties
> would be "xsi:nil" and maybe others, like "xml:lang". So, to set an
> object to nill, you'd have to look up the global property (using
> TypeHelper or XSDHelper):
>
> Property nilProperty =
> XSDHelper.INSTANCE.getGlobalProperty(
> "
> http://www.w3.org/2001/XMLSchema-instance","nil",false);
> dataObject.set(nilProperty,true);
>
> It's not easy, but doesn't have to be easy, since I consider this pretty
> much a corner case. The next question is whether or not such properties
> should appear in the instance properties of an object. My first
> impression is that they should not, they are not business properties but
> only relevant to XML serialization. But maybe someone can convince me
> that they are business relevant.
>
> It would be the user's responsibility to set this only where the object is
>
> used as the value of a nillable property.
>
> I like the second proposal, I think we are introducing something that can
> also be used to solve other problems. My reservation is that we are
> effectively making everything "half-open"... But isn't that the way XML
> is?
>
>
> Ron
> -----Ursprüngliche Nachricht-----
> Von: Frank Budinsky [mailto:frankb@ca.ibm.com]
> Gesendet: Montag, 9. Juni 2008 22:56
> An: sdo@lists.oasis-open.org
> Betreff: Re: WG: [sdo] XML Fidelity issue: xsi:nil with attributes
>
> Hi Guys,
>
> There are no restrictions on xsd:nillable. Any element declaration can
> have "nillable=true". It can have simple or complex type. So Ron is right
> that Blaise's option 2 is ruled out.
>
> My feeling is the getValue()/setValue() approach that Ron is suggesting is
>
>
> a very XML-specific concept, since it's still only used for XML purposes:
> 1) complexTypes with simpleContent and 2) for xsi:nil. If that's true,
> then it really doesn't seem right to add it to the DataObject interface.
>
> Yes, the project(Node.class) I'm suggesting would be providing a "live"
> Node-view of the DataObject. I don't really think it's that hard. It's
> very similar to the Sequence-view - just a slightly different "standard"
> API. I'd like to discuss it in this weeks call, if we can spend a little
> bit of time on it.
>
> Thanks,
> Frank.
>
>
>
>
> "Barack, Ron" <ron.barack@sap.com>
> 06/09/2008 08:48 AM
>
> To
> <sdo@lists.oasis-open.org>
> cc
>
> Subject
> WG: [sdo] XML Fidelity issue: xsi:nil with attributes
>
>
>
>
>
>
> Hi Blaise, Everyone
>
> Looking at the example in section 2.7, we see IntegerRange is simply a
> complex type, not a complex type that extends a simple type. Therefore,
> AFAICS, it has no value property.
>
> We couldn't find any limitations on which elements can be marked
> "nillable". But we are not the XSD experts, perhaps someone in the group
> can identify what (if any) restrictions exist. In any case, I assume
> Frank's example to be valid. In this case, option 2 falls out, and we
> have no way to express both that the "min" is set and that the value of
> the property is nil. I think we need some API changes.
>
> My gut feeling, however, is that Blaise is on the right track, in
> considering nillable and simple content together. The current way of
> handling complex types that extend simple context, through the
> introduction of an artificial "value" property, is problematic because it
> leads to name conflicts. We already have this on our list of issues to be
>
>
> addressed in 3.0. Perhaps we can address these issues together. One idea
>
>
> would be to create a DataObject.getValue() and a
> DataObject.setValue(Object x). We could define this value as follows
> a) if DataObject.getType() extends simple content, the value is the
> value of the simple context.
> b) if the DataObject.getType() does not extend simple content, then
> unless the user does something, the DataObject.getValue() returns the
> DataObject.
> c) the user may call DataObject.setValue(null): this sets xsi:nil to
> true when serialized to XML.
> d) unless the type extends simple context, it is an error to set the
> "value" of a data object to anything other value (eg, to another data
> object).
>
> If we want to seperate the issues, then it seems odd to have
> XMLHelper.isNil take a DataObject as a parameter. Whether something is
> nil seems not to be a character of the DataObject, but rather of the the
> property where the data object is set. That is, we can take an object
> that is used as the value of a non-nillable property, and set it as the
> value of a property that is nillable. Or the other way around. This sort
>
>
> of leads to the XMLHelper.isNil(DataObject, Property) approach, with
> corresponding setter and getter. I don't see the use case as being so
> important that we need to add the additional convenience methods.
>
> The suggesting to "project" to a DOM tree is interesting. I'm wondering
> how it differs from simply XMLHelper.save'ing to a DOMResult. Frank, are
> you imagining that the resulting DOM tree will be "live", that is, that
> changes to the DOM tree will be tracked, and immediately visible in the
> original SDO object? This seems very ambitious!
>
> Best Regards,
> Ron
>
>
> Von: Blaise Doughan [mailto:blaise.doughan@oracle.com]
> Gesendet: Freitag, 6. Juni 2008 22:25
> An: Frank Budinsky
> Cc: James Hart; sdo@lists.oasis-open.org
> Betreff: Re: [sdo] XML Fidelity issue: xsi:nil with attributes
>
> Hi Frank,
>
> For the following example from your doc (section 2.7), I think there are
> two options:
>
> <query>
> <intRange min="1" xsi:nil="true"/>
> </query>
>
> Option #1 - The property called "intRange" of type "IntegerRange" is set
> and null. This option will not round trip, since the "min" property is
> lost.
> Option #2 - The property called "intRange" is set to an instance of
> "IntegerRange" and the "min" property is set to "1" and the "value"
> property is set to null. This option will round trip.
>
> Then the problem is with the following use case? Both of the options
> below would marshal to the same XML document, but we would need to choose
> one for the unmarshal operation.
>
> <query>
> <intRange xsi:nil="true"/>
> </query>
>
> Option #1 - The property called "intRange" of type "IntegerRange" is set
> and null.
> Option #2 - The property called "intRange" is set to an instance of
> "IntegerRange" and the "min" property is unset, and value property is set
> to null. This option will round trip.
>
> ---
>
> I do not believe there is a need for the get/setNil operations.
>
> ---
>
> I see where you are going with the project to Node.class concept. Our
> EclipseLink implementation is built on top of our object-to-XML mapping
> (MOXy) technology (which also supports JAXB). We would offer the
> corresponding functionality to our users through our implementation of the
>
>
> JAXB Binder (which was designed for just this purpose). The advantage of
> the JAXB Binder approach is that it provides a specific scope in which the
>
>
> objects and the DOM are linked. If I use marshaller a new DOM is produced
>
>
> for each marshal operation, but binder will return the one linked to my
> object.
>
> -Blaise
>
>
> Frank Budinsky wrote:
> Hi James,
>
> Thanks for the quick response. I'm not sure I understand this part:
>
>
> When we marshal out then it is a simple matter of checking if the
> property isSet() and isNullable() to know if we need to print out
> xsi:nil="true".
>
>
> In addition to knowing that the property isSet and isNullable, you need to
>
>
>
> know if the value is nil ... right? The case where the value is acutally
> set to null is easy, but the case that I'm looking for a solution to is
> that the value is an object where only attribute properties are set, while
>
>
>
> the element content should be xsi:nil. I think this may be an XML-only
> concept.
>
> The more I think about this, I'm starting to wonder if this is too
> XML-specific to add to SDO? If we introduce an isNil method, like I
> suggested, that only covers the read case. We would then want to start
> thinking about adding some kind of setNil() method as well, e.g.,
> xmlHelper.setNil(myDO, "someProperty", true);
>
> So, I'm starting to wonder if an Option 4 that allows XML users to fall
> back to something like DOM and then just use it to look for the xsi:nil
> attribute, would be a better approach.
>
> For other reasons, I have been thinking about suggesting we add a new
> method to DataObject that allows one to project a DataObject to other
> interfaces:
>
> <T> T project(Class<T> targetClass);
>
> I had been thinking that such a method could be used to project to a
> Sequence "view" of the DataObject (and we could deprecate the getSequence
> method):
>
> Sequence sequence = myDO.project(Sequence.class);
>
> or it could be used to project to a static interface (instead of just
> casting - this would allow implementation to use a different instance for
> the static object):
>
> Company company = myDO.project(Company.class);
>
> and now, I think this could be the way we allow XML users to work with
> advanced XML features:
>
> Node node = myDO.project(Node.class);
>
> What do others think about this suggestion and this issue in general?
>
> Thanks,
> Frank.
>
>
>
>
>
> "James Hart" <James.Hart@Roguewave.Com>
> 06/04/2008 10:57 AM
>
> To
> Frank Budinsky/Toronto/IBM@IBMCA, <sdo@lists.oasis-open.org>
> cc
>
> Subject
> RE: [sdo] XML Fidelity issue: xsi:nil with attributes
>
>
>
>
>
>
> Our implementation has custom support for this already. I'll describe
> what we do that seems to work well.
>
> In our SDO implementation on our PropertyImpl we support a isNullable
> state which defaults to false. It also contains a isNullable() method
> that returns this state. The state can only be set during construction,
> but it defaults to false. On our Impl's for DataFactory and TypeManager
> all of our addProperty* methods have an additional method which includes
> a isNullable parameter so it can be told to create a nullable property.
>
> Our XSDHelper when constructing types simply creates the property using
> the TypeImpl API for addProperty that also exposes the isNullable
> parameter.
>
> When we marshal out then it is a simple matter of checking if the
> property isSet() and isNullable() to know if we need to print out
> xsi:nil="true". Otherwise we can print out whatever the default value
> is.
>
> I'd like to point out it doesn't matter in this case if the Property is
> has a type of DataObject or DataObjectType so it is more generic than
> the concept of xml's attributes, we just needed this concept to support
> these kind of xml documents.
>
> Saying that I don't think we need a special isNil() method, that would
> just be icing ;)
>
> I do think that the concept of data being "nill" or nullable for other
> data sets than xml is viable. For example, a DB has nullable columns
> and have defaults vs. columns that have defaults and are not nullable
> much in the same fashion of nillable attributes in schema. So I would
> prefer the benefits of making the concept nillable part of SDO's
> properties and not something that is only DAS dependant.
>
> I can also say option #2 works well because that is essentially what we
> do and it allows us to support these concepts in both our XSDHelper
> XMLHelper XMLDas and DBDas. The biggest drawback is that it increases
> the size of the in memory for every single property which is a concern
> when having to support very large data sets, but I think that currently
> is an issue with all of the state information and could be trivialized
> and a responsibility to solve as an implementation issue and not
> something that the spec has to solve.
>
> Thanks,
> James
>
>
>
> -----Original Message-----
> From: Frank Budinsky [mailto:frankb@ca.ibm.com]
> Sent: Tuesday, June 03, 2008 7:18 PM
> To: sdo@lists.oasis-open.org
> Subject: [sdo] XML Fidelity issue: xsi:nil with attributes
>
> Hi Guys,
>
> I'd like to start discussing some of the XML fidelity issues. The first
> one, hopefully easy, is to come up with a way to handle nillable
> elements
> with attributes. The problem is described in section 2.7 in this doc:
>
> http://www.oasis-open.org/apps/org/workgroup/sdo/download.php/26722/SDO_
> XML_Issues.doc
>
> Here is my first thoughts on possible solutions:
>
> Option 1: Add a helper method (to XMLHelper or maybe DataHelper if we
> think this may not be an XML-only issue) to determine if a value is nil:
>
> boolean isNil(Object value);
>
> This method would return true if value == null or if value is a
> DataObject
> with an xsi:nil tag. Users could use it something like this:
>
> if (xmlHelper.isNil(myDO.get("someValue"))) {
> // someValue is nil
> }
>
> Option 2: We could have a method that takes a DataObject and a property
> path as arguments to determine if a property is nil without actually
> getting the value:
>
> boolean isNil(DataObject object, String path);
>
> if (xmlHelper.isNil(myDO, "someValue")) {
> // someValue is nil
> }
>
> If we go with this approach we would probably want 3 methods:
>
> boolean isNil(DataObject object, String path);
> boolean isNil(DataObject object, Property property);
> boolean isNil(DataObject object, int index);
>
> Option 3: Add the methods to DataObject:
>
> boolean isNil(String path);
> boolean isNil(Property property);
> boolean isNil(int index);
>
> if (myDO.isNil("someValue")) {
> // someValue is nil
> }
>
> This is nice and clean but would only make sense if we can think of
> other
> data domains (other than XML) where the concept of nil (different from
> null) applies.
>
> Please let me know what you guys think about these suggestions, or if
> you
> have any other ideas.
>
> Thanks,
> Frank.
>
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