Object IDs vs relational keys?

> >From my background reading on object databases:
>
> "A relational database represents data relationships by having matching primary key-foreign key data. There are no data structures within the database that form links between the tables; the relationships are used as needed by joining tables. In direct contrast, a pure object-oriented database 'hard codes' its relationships by including object identifiers within an object to indicate other objects to which it is related."  (Object-Oriented Database Design, Jan L Harrington, Chapter 3)
>
> I've pored over the Magma documentation and mailing list, but couldn't find any explicit discussion of object identifiers in this context. I understand that Chris is loth to use OIDs (http://lists.squeakfoundation.org/pipermail/magma/2005-August/000027.html), so what's the alternative? What is the Magma analog of 'joining' tables using primary/foreign keys?
>
> Amir
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> Hi Amir, with Magma, every object responds to #magmaOid (It's an ugly
> name, but I prefer to be considerate of namespace, in case someone
> else wants to use #oid).  It is an integral identifier unique to that
> repository.
>
> However, in an object system, you usually don't need to do "logical"
> joins between objects via id, instead, just reference them directly.
> That is what is meant when your book mentions that ODBMS's "hard-code"
> the relationships.  They're not actually coded, they just "pre-exist"
> in teh db, rather than needing to be "looked up" over and over again..
>
> Hope this help,
>   Chris