Yes. I've been thinking about a database layer that would support indexing,
constraints, and so on. One step at a time.
(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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