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From Dain Sundstrom <d...@coredevelopers.net>
Subject Re: [persistence] Some thoughts regarding CMP and JDO
Date Thu, 07 Aug 2003 16:34:40 GMT
Hello Thomas (and the rest of the OJB team),

Jeremy Boynes and I (and a few others) wrote the CMP 2.0 implementation 
in JBoss, and we have been working on the persistence code in the 
initial Geronimo code base.

There is some code right now (a compiler and sql generator) and a 
fairly extensive design, but it looks like we have similar designs.  
The design is fairly simple from the high level.  We will support 
several front end layers simultaneously at runtime (CMP, JDO, maybe 
Hibernate, heck maybe SQL).   The job of the front end layer is to 
handle the life-cycle and callbacks required by the related 
specification, but all real work will be delegated to a centralized 
persistence service.  This persistence service handles caching, 
locking, versioning, clustering and so on.  When persistence service 
actually needs to manipulate data it delegates to a store manager 
service.  The target initial store managers include SQL 92, SQL 99, 
Oracle (which is not really SQL), file based (XML maybe), and we have 
plans to add LDAP, clustered database layer and some legacy systems.  
The following ASCI picture sums this up (if it comes through):

CMP ----------> |             | ------> SQL
JDP ----------> | persistence | ------> Oracle
Hibernate ----> | manager     | ------> LDAP
                 |             | ------> CICS (whatever)

Now the persistence manager has a huge job, so it is broken down into 
plugins for caching, locking and so on, which effectively  makes the 
persistence manager just a coordinator of the plugins.

Anyway, this is getting a little too technical for right now, 
considering the initial code doesn't even have Entity beans.  From what 
I have seen, we have a similar vision, and I think we should talk about 
merging our efforts into a common persistence engine (maybe we can even 
get Gavin and the Hibernate team to sync up with us).  I think it would 
be really positive for Java to at least have all of us at least talking 
so our systems can play well together, but if we joined forces....  :D


On Thursday, August 7, 2003, at 07:02 AM, Mahler Thomas wrote:

> Hello all,
> I'm contacting you on behalf of the Apache OJB development team
> (http://db.apache.org/ojb).
> OJB is part of the Apache DB subproject and aims at providing first 
> class
> standards based object relational mapping technology. We are currently
> finalizing our 1.0 release.
> Our team is excited to have a complete J2EE implementation at Apache 
> and we
> are willing to contribute to your project.
> OJB is heavily used in Tomcat, JBOSS and other application server
> environments and supports JTA and JCA.
> OJB provides special support for implementing BMP solutions easily.
> It provides ODMG and JDO compliant APIs.
> That's why we feel that OJB is a natural choice if you are thinking 
> about a
> persistence engine to implement CMP (and maybe JDO). We are willing to
> integrate all necessary changes into our codebase.
> Who is working on persistence concepts? Whom could we contact to get
> involved into the respective discussions?
> If you have any questions don't hesitate to contact me or the ojb 
> developer
> mailing list.
> cheers and all the best for this new project,
> Thomas Mahler
> OJB developer
> mailto:thma@apache.org

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