RE: The DOM and the victim, the iconoclast and the believer
Hi David, David said: However, note that there should be no problem with a DOM L1 client invoking a DOM L2 server, since the on-the-wire protocol for those existing methods didn't change. And if an L2 client asks whether it server has L2 functionality, it can avoid ever seeing the system exception indicating that an L1 server doesn't know about the new methods. (Didier, you implied that functionality is missing -- not!) Didier reply: David, you are right on this point. Some ORB just throw an exception when we access a non exiting member. I am actually checking where in the OMG specs it is explicitely mentionned. It discovered that it is not all ORB that has this behavior. Now the question is: Is this behavior (to throw an exception when a required member is not there) is a specified characteristic or simply because some ORB manufacturers are more clever than others. If it is specified then it is a question of conformance and now the problem is that a certain bunch of ORB provider do not play the game right. Or that simply this behavior non conformant because it is not expicitely mentionned in the specs. But, before going any further on this, I'll do my homework and try to find this in the specs. David said: Re the problems of defining a cross-language binary-compatible runtime that has a natural versioning model as well as an API that maps cleanly and efficiently to C++, Java, C, and the other languages that folk have demanded CORBA address ... well, let's just say that memory management is only one of the nasty problems that causes exquisite agony, and say that despite all the patents filed for in that area, no solution works particularly nicely. Most "ABI" standards (ABI == Application Binary Interface) only handle a small set of those issues, and haven't caught on well; to get a multi-ORB ABI going has provably demanded more than any vendor has yet wanted to support. Didier reply: Yes memory menagement is problematic, I agree. But also to have a single binary signature convention may be against manufacturers interests since I am no longer the prisoner of a single ORB vendor. David said: That said ... I think I would agree that changing already-published interfaces was pretty much against the spirit of IDL. It'd have been much more natural to define a new module (C++ namespace, Java package) that inherited the old interfaces and added new methods: no change of current interfaces/contracts. IDL has multiple interface inheritance to allow that style of evolution, among other reasons. Didier reply: Yes I agree on this, on several ORB that I made my test, inheritence is working well, so, as you said, if suffice to have the new interface to inherit from the old. That way, we know waht is part of the old contract and what is part of the new one. Or, as an alternative solution, that the client may request for a non changing interface to probe for the DOM provider support level. David said: I've been a victim in this case (don't use JDK 1.1 if you need to mix DOM implementations with different versions, JDK 1.2 is needed); and certainly an iconoclast (see above). And there's perhaps too much cynic in me lately ... ;-) Didier reply: Gee, I guess that you got the same problem as I got with JDK 1.1. This why I am not reacting, I have been also a victim :-)), and as you, an iconoclast (its natural David, you have enough experience to be a bit iconoclast in front of stupid things), I am also a believer...that _we_ can do something to correct things. PS: Thanks David for your comment about the exception raised when you access a non present member. You gave me a hint of where to check for a probable source of the problem (a) something missing in the OMG specs, (b) non conformance of several ORBs. Cheers Didier PH Martin ---------------------------------------------- Email: martind@n... Conferences: Web New York (http://www.mfweb.com) Book to come soon: XML Pro published by Wrox Press Products: http://www.netfolder.com xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev@i... Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ or CD-ROM/ISBN 981-02-3594-1 Please note: New list subscriptions now closed in preparation for transfer to OASIS.
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