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Subject: AW: AW: [sdo] ISSUE 5: Defining SDO types by JAVA types
Hi Frank, Well, the spec says "null if not found", so I guess it all comes down to how hard an implementation looks ;-) I alway interpreted "found" to mean that the implementation is capable in finding and generating SDO metadata based on reflection of the class parameter. Even if you consider it a breaking change, I doubt any of our customers are currently relying on the value null being returned, e.g., I doubt any code will break if we add intelligence to the getter. It's not the consistency with the other getType that bothers me with implicitly definiting types, it's simply that I don't think the average user expects a "getter" to do anything, only to retrieve values from some kind of store. So the "principle of least surprise" would argue for the behavior you suggest. On the otherhand, all we are really talking about here is lazy initialization of the type, which is not that uncommon for getter. And the effect of your API is that we are going to force the user into constucts like Type fooType = typeHelper.getType(Foo.class); if (fooType == null) { fooType = typeHelper.defineType(Foo.class); } everytime he want to get a type. The same is construct will have to be used of DataFactory.create(Class), which is defined as relying on TypeHelper.getType(). And this is probably the standard way of creating static SDOs, right? Doing this every time you want to create a static SDO is a chore. What's the point of placing this extra burdon on the user? Why not add the intelligence to the implementation, and save the users the "if". This last point (IMO) trumps the "principle of least surprise". It's something for which it's hard to think of a compromise. I guess we'll just have to settle this one with a vote. Ron ________________________________ Von: Frank Budinsky [mailto:frankb@ca.ibm.com] Gesendet: Mi 10.09.2008 21:01 An: sdo@lists.oasis-open.org Betreff: Re: AW: [sdo] ISSUE 5: Defining SDO types by JAVA types Hi Ron, After giving it some thought, I think that TypeHelper.getType(Class) should not implicitly define types. We should instead add one or more define methods that take classes as input. The problems with TypeHelper.getType(Class) defining types are: 1) it would be a breaking change (currently the spec says it returns null if the type is not found). 2) it would be inconsistent with the way TypeHelper.getType(uri, name) works. I would think it would be odd to see this kind of behavior: type = typeHelper.getType("someURI", "Person"); // return null type = typeHelper.getType(Person.class); // return non null type = typeHelper.getType("someURI", "Person"); // return non null If we did this, I think we might also want getType(String, String) to do implicit type definition (for example, check on the class path if there is a Class that, if defined, would have the correct name and URI. We could consider this .... but personally, I think it's better to just keep getType() as a read-only API with no side-effects. As far as what kinds of annotations we might want to support, I think that we could maybe handle it like bindings ... e.g., have various define methods like: JAXBBindingHelper.defineType(Class), JPABindingHelper.defineType(Class), etc. Each knows about binding-specific annotations, and knows how to produce SDO metadata from them. Anyway, just a thought. Frank "Barack, Ron" <ron.barack@sap.com> 09/10/2008 04:55 AM To <sdo@lists.oasis-open.org> cc 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 --------------------------------------------------------------------- To unsubscribe from this mail list, you must leave the OASIS TC that generates this mail. 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