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From Aleksei Lukin <lu...@stu.cn.ua>
Subject Re: OCM:To Path or Not to Path
Date Wed, 08 Oct 2008 08:07:16 GMT
Wednesday 08 October 2008 10:16:07 Boni Gopalan (BioImagene) написав:
> Let me take a challenge I am facing right now to give the context of why
> identities other than UUID is important - may be this is something specific
> to the OCM interpretation.
> I mapped Foo , with mix:referenceable and by specifying an UUID field on
> the the bean. I saved an instance of Foo. After some time I archived that
> Instance (A normal enterprise requirement).  After some more time user
> requests a restore.  Now if I restore using the same OCM layer I am going
> to get a different UUID.  It is not desirable at all.  I would like the
> state of the object to be restored just as it was before: including the
> jcr:uuid.

Lets decide what realluy we  backup and restore. 
If you backup you make copy of object therefore you make ANOTHER object that lives on it's
own and original object lives on it's own. 
So it is 2 different objects in any meaning.
If repository does a copy it changes UUID for copy. If you do backup somewhere outside repository
you can not use UUID of a copy anymore as primary key, you must save old UUID 
somewhere in backup copy as reference to original object and create new one for a copy.  Thus
your restore code must handle UUID specially. JCR import/export code has options 
for UUIDs that allows to use UUIDS from system XML view or ignore them at import.

We can think of UUIDs as a C/C++ pointers in infinite abstract memory. Each object lives somewhere
and we can say to universe-wide MMU :) to find it.

> So the simple notion of UUID being unique alone is not sufficient.  What
> about a notion of UUID : <scope = "usecurrentifprovided">?
> OCM fully acknowledges this and has provided the notion of "id" through
> "id=true" attribute.  I feel, for the completeness of such a notion we need
> the ability to attach an ID generator with the intelligence of not
> generating a new ID if one is provided.

Do not think that id purpose to be some unique key. OCM just creates node with such name.
May be Christphe needs it for collection mapping or whatever else...
> Thanks
> Boni

SY, Alex Lukin

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