Deployment descriptors.
In EJB, deployment descriptors are used to address
issues of synchronization, persistence, transactions, etc.
separately from the base code. A similar approach is used
in Demeter/Java (and in AOP in general)
where the synchronization and remote invocation
aspect are treated separately.
See the following message
To: EJB-INTEREST@JAVA.SUN.COM
Subject: EJBs and Aspect-oriented programming
From: Carl Jones
Reply-To: A mailing list for Enterprise JavaBeans development
I have just come across the subject of aspect-oriented programming
(see http://www.parc.xerox.com/spl/projects/aop/) and can see a number
of parallels between it and EJB development.
Aspect-oriented programming (AOP) allows the modelling of behaviour
that "cross-cuts" a number of objects. To me, it would seem that EJBs
currently support at least four such aspects; persistence, transactions,
security and concurrency.
The idea with AOP is that an aspect is defined along with a "weaver" that
weaves the aspect's code into the selected class.
If these parallels are correct, it seems to me that we have a modeling
concept that should be used in the EJB specification and which would allow
for the addition of new aspects to the EJB model over time, say replication.