On Thu, 1 Mar 2001, Alex Smith wrote:
> Dan O'Connor <[EMAIL PROTECTED]> writes:
>
> >Tyler Jewell, the BEA training director for Java and XML
> >technologies, yesterday published an article called "What's Wrong
> >with the EJB 2 Specification" at
> >http://www.onjava.com/pub/a/onjava/2001/02/28/ejb.html. In this
> >article, he identifies "dependent objects" as what is wrong with the
> >EJB 2 specification.
>
> Good article. I do agree that Tyler's objections are misplaced.
>
> >First, I would like to correct what I believe was a fairly basic
> >technical mistake in Tyler's article. He says, "Dependent objects
> >don't require primary keys." I would like to suggest that the
> >opposite is the case, and I cite from 9.4.4.1 in the spec (proposed
> >final draft): "The dependent object class instance must have a
> >primary key value that is unique across all instances of the
> >dependent object class."
>
> This is a mistake in the spec rather than the article -- dependent objects
> should not have an identity of their own else they would no longer be
> dependent. If you use a relational model to color your perception of the
> world, a dependent object may or may not have its "own" (i.e. not composed
> from the keys of its parent) primary key. Some data modeling methodologies
> recommend creating a unique physical key for each and every entity, a
> practice I don't subscribe to. On the other hand if you think in terms of
> objects, a dependent object belongs to the parent and therefore cannot have
> an identity other than that of its parent.
I'd say that the dependent object has no identity that is meaningful
outside of the context of its parent. If you have three dependent
instances of the same class associated with the same parent, they must
have their own identities if you do not consider them equivalent, right?
>
> I think the spec should provide support for dependent objects with a primary
> key but not require it.
>
> The rest of Dan's comments are right on target.
>
> Alex Smith
> Insight LLC
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--
Dan Christopherson (danch)
nVisia Technical Architect (www.nvisia.com)
Opinions expressed are mine and do not neccessarily reflect any
position or opinion of nVISIA.
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