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Subject: Re: DM Rule #5: References considered harmful.
From: Felix Meschberger <fmeschbe@gmail.com>
To: users@jackrabbit.apache.org
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Date: Mon, 09 Jul 2007 08:16:46 +0200
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Hi David,

I have the issue of creating a caching system, where I have my cache
entries, which have dependencies of certain data. Of course, I would not
create REFERENCEs to the real data to not lock down the user managing
the data. But how about creating a mirror hierarchy of data to which the
cache entries REFERENCE.

In this case, when the real data is modified I can lookup the mirror and
find the referring cache entries. The nice thing of having a REFERENCE
property in this case is, that I can get the referents from the data
(actually the mirro of it) node without having to employ a heavy weight
search.

What do you think ?

Regards
Felix

Am Samstag, den 07.07.2007, 13:20 +0200 schrieb David Nuescheler:
> Explanation
> ---
> References imply referential integrity. I find it important to
> understand that references do not just add additional cost for the
> repository managing the referential integrity, but they also are
> costly from a content flexibility perspective.
> 
> Personally I make sure I only ever use references when I really cannot
> deal with a dangling reference and otherwise use a path, a name or a
> string UUID to refer to another node.
> 
> Example
> ---
> Let's assume I allow "references" from a document (a) to another
> document (b). If I model this relation using reference properties this
> means that the two documents are linked on a repository level. I
> cannot export/import document (a) individually, since the reference
> property's target may not exist. Other operations like merge, update,
> restore or clone are affected as well.
> 
> So I would either model those references as "weak-references" (in JCR
> v1.0 his essentially boils down to string properties that contain the
> uuid of the target node) or simply use a path. Sometimes the path is
> more meaningful to begin with.
> 
> I think there are usecases where a system really can't work if a
> reference is dangling, but I just can't come up with a good "real" yet
> simple example from my direct experience.