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Subject: AW: [sdo] ISSUE 5: Defining SDO types by JAVA types


Hi Everyone,

During the call on Sept. 2, we decided it would be best to limit the scope of ISSUE 5 to the API question below, that is, the question of whether "TypeHelper.getType(Class)" can implicitly use introspection to define types, or whether we need an explicit "TypeHelper.defineType(Class)".

Resolving ISSUE 5 along the lines of either proposal at least signifies that Java classes are legitimate sources of metadata, that it is possible to round-trip between static SDOs and SDO Types.

The actual annotations (or side files) used to derive the metadata (or to augment the metadata that is already available through reflection) can then be discussed in a seperate issue, which we can open as a part of the resolution of this ISSUE 5.

The interesting discussion here is to which extent can we use already existing standards, JPA and JAXB, as annotations.

Ron


-----Ursprüngliche Nachricht-----
Von: Barack, Ron [mailto:ron.barack@sap.com] 
Gesendet: Freitag, 1. August 2008 01:14
An: sdo@lists.oasis-open.org
Betreff: Re: [sdo] ISSUE 5: Defining SDO types by JAVA types

Hi Blaise,

I can only say I had option 1 in mind.  The only item from option 2 I
think would be really nice to have is support for Qname for the URI
types...it's just that the string format defined by SDO requires that
clients write their own parsers, and anyway, the only reason we don't
support Qname for type anyway is that SDO is older than Java 1.4, where
Qname became part of the JDK.  The different calandar classes would be
worth supporting, too.

Annotations are something I wish we could live without, or rather, I
wish we could use JAXB's (or someone elses) annotations.  Unfortunately,
the match really isn't very good:  JAXB is very efficient in that it
captures enough information in the annotations so that the XML can be
produced (note, there is no round tripping of the XSD), but we want to
capture the SDO metadata, we want to round trip SDO -> Static SDO ->
SDO...I see the Java interface as a valid alternative to XSD for storing
(non-XML oriented) metadata.  On the other hand, JAXB has use cases that
are really complex, complete support of JAXB annotations is really a
daunting task.  Bottom line, I think we do need to define our own
interfaces.  I put forward a proposal for the annotations some time ago,
basically it documents how our implementation already works.  You can
find it here:
http://www.oasis-open.org/apps/org/workgroup/sdo/download.php/26370/sd03
0_annotations.doc

I'm pretty curious what others think about the idea of defining our own
annotations.

Best Regards,
Ron



Subject: Re: [sdo] ISSUE 5: Defining SDO types by JAVA types

From: Blaise Doughan <blaise.doughan@oracle.com> 
To: sdo@lists.oasis-open.org 
Date: Tue, 29 Jul 2008 11:41:49 -0400 

------------------------------------------------------------------------
--------

Title: ISSUE 5: Defining SDO types by JAVA types
What is the intended scope for this issue?:

Option #1:  Define Types from SDO Compatible Interfaces
For me the minimum bar for this feature is to ensure that interfaces
that can be generated from an XML schema can themselves be the source of
the SDO metadata.  Presumably we would also require that all generated
interfaces contain the necessary annotations (just as JAXB 2.X does with
its generated classes).

Option #2:  Define Types from Any Interface
Similar to option #1, but a heck of a lot more work.  We would need to
devise ways of handling all possible Java types including:

javax.xml.namespace.QName 
org.w3c.dom.Element 
java.util.Calendar 
javax.xml.datatype.XMLGregorianCalendar 
java.util.Map 
org.mydomain.foo.Employee (a POJO not an interface)

Option #3:  Somewhere between Option #1 and Option #2
Somewhere between option #1 & option #2, although we should decide where
the line will be drawn.

-Blaise

Barack, Ron wrote: 
Hi Everyone, 

The current discussion of containment is in large part motivated by the
wish to use other sources of metadata as a standard way to define types.

Although we at SAP have always interpreted the spec as at least allowing
this, we're probably alone in that interpretation.  The spec is at best
very unclear about how this should be done.

One possibility is to interpret TypeHelper.getType(Class) as performing
introspection of the class, and returning a type based on this
introspection.  In order to standardize this behavior, all we'd need to
do is change the second bullet point in 4.8.2 from

getType(Class interfaceClass) returns the Type for this interfaceClass
or null if not found. 
To something like 

getType(Class interfaceClass) returns the Type for this interfaceClass.
If the interfaceClass is not already associated with a Type, the class
will be introspected according to the algorithm in Chapter 6,
recursively creating Types as needed for all classes directly or
indirectly referenced by interfaceClass. 

This is probably fairly surprising behavior.  From the usability
standpoint, most people don't expect a getter to do anything other than
look up a value.  On the other hand, this is really nothing more than a
form of lazy initialization.  The ClassLoader associated with the helper
context is implicitly loaded when the helper context is created.

If we want to define a new method, then need to do a little more work,
and define a method like 

defineType(Class interfaceClass) returns the Type for this
interfaceClass.  If the interfaceClass is not already associated with a
Type, the class will be introspected according to the algorithm in
Chapter 6, recursively creating Types as needed for all classes directly
or indirectly referenced by interfaceClass. 


Note that neither proposal requires us to solve the knottier issue of
how the class is introspected, and converted to a SDO type.  This is
just putting another stake in the ground, saying that Java classes can
be introspected, can be sources of metadata, and that this is the API
for doing it.



Best Regards, 
Ron 


 sd

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