[elephant-devel] Re: Derived Indicies

[Alex Mizrahi]

 IE> Given that in Elephant, the cost of a btree instance is negligable,

it postmodern backend each btree is backed by a database table,
so i think it's not that negligable there..

 IE> one way to do this is the just have a set of messages for each user in
 IE> a user slot (a pset or set-valued slot).

but i think it's quite easy to make cheap psets -- just a dup-btree of 
pset-oid->item

 IE> messages.  Of course to get the full efficiency you want, we'd have to
 IE> make a sorted-pset that sorts on some fn of the elements.

sorted-pset? how can we sort something in database without having a key?

i think that would be more like indexed-pset, with indices being btrees.

as an interface, it could look like:
   (get-by-range (messages-of user) 'date yesterday nil)

but, damn, it would be much harder to make cheap btrees with SQL..

 IE> I'd like to think about different metaphors for solving these problems
 IE> so we don't end up turning Elephant's interface into a less efficient
 IE> variation of an ORM!

i thought elephant is a BDB wrapper :)