Same thing has been bothering me as I am about to embark on fairly large EJB
based project.
IMO this is one of the major questions which needs to be addressed by the
EJB dev community. There are many OO systems that have domain object models
as a conerstone of their design. Most of these models involve complex
inheritence and association relationships. Polymorphic behaviour is
important in this modeling.
I have been following this discussion group and I am yet to come across a
suggestion of a reasonable pattern for implementing DOM's in an EJB based
environment. Most threads where this is discussed end up in a debate around
the evils of inheritence as opposed to delegation.
This to me is missing the point. The issue is: we have inheritence in OO
analysis, design, and implementation. It is a powerfull tool when used
correctly. The Java environment itself relies heavily on it and encourages
it use in the programming model, and yet to my knowledge there is no clear
and simple way for using it with EJB's.
DOM's usually reflect:
- "entity" (Jacobson) type objects involved in the problem domain.
- These entity objects have state.
- The state needs to persist beyond the lifecycle of one process
- There a generalizations and specializations of entities.
- They are involved in units of work (transacions)
Entity EJB's seem to be the perfect answer at an implementation level for
dealing with these requirements.
Echoing Michael's question: What then are strategies/patterns for
implementing domain objects to entity EJbeans?
Clyde.
-----Original Message-----
From: Michael Schuerig <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED] <[EMAIL PROTECTED]>
Date: 06 July 1999 10:23
Subject: Entity bean granularity
>My understanding is that entity beans are meant to be components that
>may realize parts of design models encompassing more than a single
>class. Now, this sounds fine in the abstract, but what are the concrete
>consequences? Let me put it like this:
>
>- Taking the usual multi-tier stuff for granted, what are the specific
>influences of EJB on design?
>- What strategies are there to allocate domain objects to entity beans?
>- What strategies are there to allocate functionality to session beans?
>(Is it reasonable to represent Jacobson's "control classes" through
>session beans?)
>
>TIA,
>Michael
>
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