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Subject: Re: AW: [sdo] Revised Proposal for Static SDOs.doc


Hi Ron,

Some additional comments on the proposal:

General Comments

What package will the annotations be put in, commonj.sdo.annotation?

Are we requiring that the Interfaces generated from XML schemas contain the proposed annotations?



From Section 1.1 - Compliance Points


"While it is expected that implementation will provide a means to generate static interfaces based on schema and/or other sources of metadata, the precise API for generation of static SDO is out-of-scope for this specification.  Compliance is based on the ability to use generated interfaces as a source of metadata and as a means of accessing data.  Interoperability is achieved because the interfaces of the static SDOs, and clients that rely on them and their mapping to SDO metadata, can be used with any compliant SDO implementation regardless of how the static SDOs were generated."


It is possible to test the generated interfaces.  The JAXB TCKs do this by making the class generation step pluggable, implementors write a TCK/compiler bridge so that the TCK can generate classes using that implementation.  I'm not saying we need to do it, only that it is possible.


From Section 1.6 - Generation of SDO Types from Static SDOs

Base Type
For the base type, are we going to include any special exclusions such as if your interface extends java.io.Serializable then your type is not expected to have a base type with instance class java.io.Serializable?

Containment Default
Presumably the goal of annotations is to require as few of them as possible, where the defaults are normally good enough and the user only specifies annotations when they need to override default behaviour.  If the predominant use of SDO is with XML then containment should default to true, otherwise it will appear annotation heavy when compared to technologies such as JAXB.

Data Type Properties
"If [javaType] is not a static SDO, then the implementation may create a property with any of SDO’s defined data types, so long as the selected data type is compliant with the Java type, according to the rules of Chapter 6."
Isn't this point overridden with the table below it?


From Section 1.7.2 - @SdoOpenContentProperty

"When @SdoOpenContentProperty is used to annotate a Java type, then its “type” attribute is ignored."
I find the above statement confusing.  I think if the type is not specified then it defaults to the owning interface, but if it is specified then it should either be used or an error condition should be thrown.  It would be confusing for the property to be a type other than the one specified.

How do we specify the XML representation of open content properties?

From Section 1.8.2 -
@SdoIncludePackage

Can you further explain this annotations?


-Blaise


Barack, Ron wrote:
Hi Frank,

Good catch regarding the wording of JavaHelper.define()... Yes, the proposal for static SDOs (as was pointed out during the presentation  during the vF2F) requires interfaces as static SDOs be supported.  I think that JavaHelper.define() should work the same way.  Interfaces MUST be suppported, vendor extensions (to POJO or generated classes) are allowed.  The reason for this is to achieve portability across SDO implementations.

Regarding the use of JAXB annotations as a source of SDO metadata, we've had serveral mail threads on the topic, for instance this http://www.oasis-open.org/apps/org/workgroup/sdo/email/archives/200901/msg00036.html
And before that http://www.oasis-open.org/apps/org/workgroup/sdo/email/archives/200811/msg00007.html
Everyone, myself included, would have liked to replace static SDOs with JAXB POJOs.  Unfortunately, especially when it comes to being a source of metadata, an implementation can't really do better than what the client can already do himself, call JAXBContext.generate and pass the result to XSDHelper.

Regarding the three required ways for defining types in SDO:  the current proposal has nothing to do with it, this was already decided when we added JavaHelper.define().

Regarding the "optional" ways of defining types:  these are not really optional features, they are vendor extensions.  As I wrote above, I don't think defining types based on JAXB is very realistic, at least not as an implementation feature.  I'm strengthend in this belief also by EclipseLink's JAXBHelperContext, which you notice does not use the JAXBs themselves as sources of metadata.

I don't see much of a differnce between supporting POJOs and JPAs as sources of metadata, except that for instance an implementation might want to consider @Id and @SdoKey to be synonymous.  A clever implementation could also analyse the mapping and determine bi-directional properties.  But unlike JAXB, the mapping between the JavaBean and the SDO properties is pretty one-to-one.  In other words, if an implementation chooses to allow POJOs as static SDOs, they are already very close to a solution for JPA integration. 

As far as use-cases are concerned, it comes down to the same discussion we've had before.  If SDO is supposed to provide a representation for data that is independent of the source of the data, then it's pretty awkward that the only easy way to define types is XML schema.  (To me, the TypeHelper.define() method is almost an SPI method, useful for implementing DAS's but not something I expect business services to have to provide.)  If XSD is the only way to define types in SDO, then we need to change the definition of SDO to providing a representation for data that is independent of the source of the data, provided that source is XML.

My comments above are all about using JAXB as a source of metadata.  Of course, JAXB integration (as far as moving data between SDO and JAXB, or some kind of wrapping approach) is something we'd really like to see.


Ron

-----Ursprüngliche Nachricht-----
Von: Frank Budinsky [mailto:frankb@ca.ibm.com] 
Gesendet: Donnerstag, 26. Februar 2009 23:22
An: sdo@lists.oasis-open.org
Betreff: Re: AW: [sdo] Revised Proposal for Static SDOs.doc

Hi Ron,

First of all, I want to say that the annotation design looks fundamentally 
good to me. 

My question is what exactly is this requiring of an implementation? In 
Section 2.9.1 of sdo-java-3.0-spec-cd01.doc it says this about JavaHelper: 
"Implementations may impose limitations on the classes given as arguments 
to the define and create methods. Some implementations may allow only 
interfaces to be given, others may allow POJO classes, other 
implementations may allow only classes that extend some implementation 
dependent base class to be used.".

Does this mean that it is optional whether or not implementations support 
defining metadata using interfaces with these annotations? My guess is 
that you're answer is no. If so, then I would like to better understand 
what exactly the SDO 3 story is regarding creation of metadata. 

In SDO 2, we had the following story:

1. define with XML Schema     required
2. define programmatically    required
3. define with other sources  optional (impl specific)

The proposal for SDO 3, as I understand it:

1. define with XML Schema     required
2. define programmatically    required
3. define with static SDO     required
4. define with POJO classes   optional (w/JavaHelper)
5. define with JAXB classes   optional (w/JavaHelper)
6. define with JPA classes    optional (w/JavaHelper)
7. define with other sources  optional (impl specific)

Do I have this correct? My concern with #3 being required is that if an 
impl (e.g., IBM's) wants to support #5, we're forced to support two 
competing ways of doing the same thing. In our use case, we want to use 
JAXB, but would be forced to provide users with two options. It 
complicates things, because now we need to explain which one should be 
used when. Since our use case is XML-centric and we want to use JAXB, the 
standard static API for XML, our answer will always be to use JAXB. To us, 
the static SDO alternative is only interesting when the canonical metadata 
representation is not XML Schema, but that is not a use case we currently 
want to support with our impl.

Comments?

Thanks,
Frank. 




"Barack, Ron" <ron.barack@sap.com> 
02/26/2009 09:34 AM

To
"Barack, Ron" <ron.barack@sap.com>, "Blaise Doughan" 
<blaise.doughan@oracle.com>
cc
<sdo@lists.oasis-open.org>
Subject
AW: [sdo] Revised Proposal for Static SDOs.doc






Hi Blaise,
 
Embarrassing mistake here:  annotations do not allow "extends" clauses. In 
that case, I have a slight preference for the proposal as it is currently 
written up, since it allows the user to either make something an element 
explicitly or to allow SDO to decide itself.  That said, I really don't 
want to hold up accepting this proposal based on this issue.  If this is 
the only thing that is hold you back from supporting the proposal, let me 
know and I will replace my @SdoXmlElement and @SdoXmlProperty with the 
annotations you have specified.
 
For everyone else, the proposal was reviewed and discussed at the vF2F, I 
think there is consensus here.  I'd like to resolve ISSUE 22 (as well as 
ISSUE 13, ISSUE 25, ISSUE 28 and ISSUE 29) at Tuesday's meeting.
 
Ron
 

Von: Barack, Ron [mailto:ron.barack@sap.com] 
Gesendet: Dienstag, 24. Februar 2009 15:05
An: Blaise Doughan
Cc: sdo@lists.oasis-open.org
Betreff: AW: [sdo] Revised Proposal for Static SDOs.doc

Hi Blaise,
 
I was thinking that "null" would mean "normal SDO rules (for determining 
if a property is an attribute or element) apply".   With a 2 valued enum, 
the runtime would have no way of knowing if the programmer expressed a 
wish regarding isElement or not.
 
Since they share the "name" and "uri" properties, maybe @SdoXmlProperty 
can be a base type extended by @SdoXmlAttribute and @SdoXmlElement? 
 
Ron
 

Von: Blaise Doughan [mailto:blaise.doughan@oracle.com] 
Gesendet: Dienstag, 24. Februar 2009 14:50
An: Barack, Ron
Cc: sdo@lists.oasis-open.org
Betreff: Re: [sdo] Revised Proposal for Static SDOs.doc

Hi Ron,

How about dropping @SdoXmlProperty and enhancing @SdoXmlAttribute and 
@SdoXmlElement?  Where do you see the node type being null?

    @Retention(RetentionPolicy.RUNTIME)
    @Target(@Target({ElementType.METHOD,   ElementType.FIELD})
    public @interface SdoXmlElement {
        String name() default "";
        String uri() default "";
     }

    @Retention(RetentionPolicy.RUNTIME)
    @Target(@Target({ElementType.METHOD,   ElementType.FIELD})
    public @interface SdoXmlAttribute {
        String name() default "";
        String uri() default "";
     }

-Blaise

Barack, Ron wrote: 
<<Proposal for Static SDOs.doc>> 
Hi Everyone, 
Attached is a new proposal in which I've tried to incorporate all the 
comments I got during the F2F on Friday.  Blaise, I've broken out 
@SdoXmlElement seperately rather than keeping it a part of @SdoXmlProperty 
because annotations don't allow default values to be null, and I think 
implementations need to distinguish whether the user has actually said 
anything or not.  Otherwise, we'd need a three-valued enum, and I just 
think that's too ugly.
Comments welcome, maybe we can discuss this on Tuesday's call. 

Ron 

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