Hi Erik!
-----Original Message-----
From: Eric R. Williams
To: [EMAIL PROTECTED]
Sent: 2/22/99 10:57 AM
Subject: Re: Pass-by-Value (was:RE: Question regarding Session and Entity
Beans)
Richard,
Correct me if I'm wrong... but wouldn't the lack of support
for Serializable types make the implementation non-compliant
with the EJB spec? Can you list the servers which do not
support graphs of Serializable objects?
**************
Well, yes. EJB servers are supposed to support Java RMI which includes PBV.
Unfortunately, EJB servers based on CORBA have a handicap in that CORBA PBV
spec is still young and not universally implemented. This will change over
time, but for now most (if not all) CORBA based EJB servers do not support
PBV.
**************
I looked at your PBV paper... and it has some interesting
ideas. I don't think that atomicity and immutability are
absolutely necessary, but I agree with the dependent and
fine-grained criteria. You should be able to specify as
complex a data/view model as required. And clients should
be able to update the objects and send them back to the
server (not in all cases, but when it makes sense).
*************
I think you have to take that paper at face value. Its a strategy that I,
and probably others, believe is best for creating CTM applications. Even if
you take away some, but not all aspects of this strategy, I would consider
the paper to be a success.
Personally, I will follow the guidelines outlined in the PBV paper as much
as possible because I have some experience with this and other strategies
and have found the guidelines in the PBV paper to work the best.
*************
-eric
Richard Monson-Haefel wrote:
>
> Personally I think this issue about passing partial object graphs is
> irrelevant in some ways. Two issues come to mind:
>
> First not all CORBA implementations of EJB support Java serializable
types,
> most allow standard CORBA structs but not PBV as we are used to in
Java RMI.
> In these cases you have to develop your PBV objects to be very simple
with
> public attributes so that it can double as CORBA structs if necessary.
>
> Second, PBV should be done with care. I have outlined some ground
rules for
> PBV in a paper I submitted to the EJB workshop
>
(http://www.inprise.com/events/ejbdesign/submissions/Pass-by-Value.html)
.
> Generally, PBV is a bad idea in Component Transaction Monitor (CTM)
> applications because of problems with object equivalence and
performance.
> You can use PBV as described in my paper, but anything more
complicated will
> cause problems in the long run.
>
> You can't design EJB solutions like business object systems because
you are
> dealing with solutions that span address spaces. Your approach needs
to be
> completely different stressing the use of session beans to manage
workflow
> and act as an interface to your clients (applets, servlets, etc.), and
> limited use of entity beans on the client. Entity bean should focus
on
> consistent and safe access to related data.
>
> There is a lot more to this than meets the eye and there is no way I
can
> cover it all in an e-mail - a book maybe.
>
> Thanks,
>
> Richard
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