Easy enough to do. The only drawback is I'd probably want to force it into
a hash during the query. For large datasets (say 100,000 records) this
might get expensive.
On Wed, Feb 18, 2009 at 4:13 PM, Rich Hickey <richhic...@gmail.com> wrote:
>
>
>
> On Feb 18, 3:51 pm, Jeffrey Straszheim <straszheimjeff...@gmail.com>
> wrote:
> > Yes. I've been thinking about a database layer that would support
> indexing,
> > constraints, and so on. One step at a time.
>
> Maybe I wasn't clear, I'm talking about the foundational layer.
> Instead of:
>
> (def data {
> :table-1 #{ { :x 34 :y 33 } { :x 33 :y :fred } { :x "k" :y \u } }
> :table-2 #{ { :a "fred" :b "mary" } { :a "sally" :b "joan" } }
> })
>
> I'm recommending:
>
> (def data
> #{{:rel :table-1 :x 34 :y 33 }
> {:rel :table-1 :x 33 :y :fred }
> {:rel :table-1 :x "k" :y \u }
> {:rel :table-2 :a "fred" :b "mary"}
> {:rel :table-2 :a "sally" :b "joan" }})
>
> i.e. making relation and rule names non-special.
>
> Rich
>
> > (logic-rule (:fred :x ?x :y ?y) - (:sally :x ?x :z ?z) ("becky" :y ?y)
> > (not! :janet :qqq ?z) (if < ?x ?y))
> >
> > Translated into positional notation (assuming the columns are named in
> the
> > obvious way):
> >
> > fred(X,Y) :- sally(X,Z), becky(Y), ~Janet(Z), when X<Y.
> >
> > The "<" symbol can be any Clojure callable. Its return value will be
> > interpreted as a boolean.
> >
> > So, you'd get every X,Z from the relation sally, cross product with every
> Y
> > from becky, remove each tuple that has a Z in janet, and also remove any
> > tuple where X<Y fails. The resulting X,Y would be projected as relation
> > fred.
> >
> > On Wed, Feb 18, 2009 at 3:23 PM, Rich Hickey <richhic...@gmail.com>
> wrote:
> >
> > > On Feb 9, 8:46 am, Jeffrey Straszheim <straszheimjeff...@gmail.com>
> > > wrote:
> > > > No, but I'm really learning as I go here. I'll look into it.
> >
> > > > On Mon, Feb 9, 2009 at 7:58 AM, Rich Hickey <richhic...@gmail.com>
> > > wrote:
> >
> > > > > Looks like you're moving apace!
> >
> > > > > Have you considered query/subquery optimization instead of magic
> sets?
> >
> > > > > Rich
> >
> > > > > On Feb 8, 7:51 pm, Jeffrey Straszheim <straszheimjeff...@gmail.com
> >
> > > > > wrote:
> > > > > > By the way, if anyone on this list has experience implementing
> > > bottom-up
> > > > > > optimizations for logic programs, particularly from the magic set
> > > family,
> > > > > > and is willing to assist, please contact me.
> >
> > > > > > On Sun, Feb 8, 2009 at 7:47 PM, Jeffrey Straszheim <
> >
> > > > > > straszheimjeff...@gmail.com> wrote:
> >
> > > > > > > Stratified negation is working and in trunk.
> >
> > > > > > > I have some cool ideas of a simple, but powerful, way to
> implement
> > > > > > > evaluable predicates. They'll likely make it in by midweek.
> >
> > > > > > > The the hard part (magic sets) begins.
> >
> > > > > > > On Feb 8, 11:43 am, Jeffrey Straszheim <
> > > straszheimjeff...@gmail.com>
> > > > > > > wrote:
> > > > > > > > I now have recursive queries working. My next 3 milestones
> are
> > > > > > > stratified
> > > > > > > > negation, evaluable predicates, and then some version of
> magic
> > > sets
> > > > > > > > optimization. But now, as long as your queries are
> non-negated
> > > it is
> > > > > > > > working.
> >
> > > > > > > >http://code.google.com/p/clojure-datalog/
> >
> > > I got a chance to look at your docs:
> >
> > >http://code.google.com/p/clojure-datalog/wiki/BasicSyntax
> >
> > > I think your choice of using maps (we don't call them hashes in
> > > Clojure as they might not be hash tables) is right on the money for
> > > Clojure, especially set-of-maps-is-relation, just like clojure.set.
> >
> > > Two thoughts:
> >
> > > I wonder though if the map of rel-names to rels isn't a wart though.
> > > It's a pet peeve of mine that relation names don't end up in the db
> > > like any other attribute. Yes, they'll need to be indexed, but
> > > eventually you'll want to support indexing on any desired attributes
> > > as well. Putting relation names in the db gives you a uniform meta-
> > > query capability. I haven't thought this all the way through, but you
> > > might want to think about it.
> >
> > > I didn't know how to interpret this:
> >
> > > (logic-rule (:fred :x ?x :y ?y) - (:sally :x ?x :z ?z) ("becky" :y ?y)
> > > (not! :janet :qqq ?z) (if < ?x ?
> > > y))
> >
> > > Overall, it looks very promising!
> >
> > > If you weren't aware of it:
> >
> > > Foundations of Databases: The Logical Level
> > > Serge Abiteboul, Richard Hull, Victor Vianu
> >
> > >http://www.amazon.com/gp/product/0201537710
> >
> > > has good coverage of Datalog, including QSQ.
> >
> > > Rich
> >
>
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