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;; Copyright (c) Jeffrey Straszheim. All rights reserved. The use and
;; distribution terms for this software are covered by the Eclipse Public
;; License 1.0 ( which can
;; be found in the file epl-v10.html at the root of this distribution. By
;; using this software in any fashion, you are agreeing to be bound by the
;; terms of this license. You must not remove this notice, or any other,
;; from this software.
;; database.clj
;; A Clojure implementation of Datalog -- Support for in-memory database
;; straszheimjeffrey (gmail)
;; Created 21 Feburary 2009
(ns clojure.contrib.datalog.database
(:use clojure.contrib.datalog.util)
(:use clojure.contrib.def)
(:use [clojure.set :only (union intersection difference)])
(:use [clojure.contrib.except :only (throwf)])
(defstruct relation
:schema ; A set of key names
:data ; A set of tuples
:indexes) ; A map key names to indexes (in turn a map of value to tuples)
;;; DDL
(defmethod print-method ::datalog-database
[db #^Writer writer]
(binding [*out* writer]
(println "(datalog-database")
(println "{")
(doseq [key (keys db)]
(println key)
(print-method (db key) writer))
(println "})"))))
(defn datalog-database
(with-meta rels {:type ::datalog-database}))
(def empty-database (datalog-database {}))
(defmethod print-method ::datalog-relation
[rel #^Writer writer]
(binding [*out* writer]
(println "(datalog-relation")
(println " ;; Schema")
(println " " (:schema rel))
(println " ;; Data")
(println " #{")
(doseq [tuple (:data rel)]
(println " " tuple))
(println " }")
(println " ;; Indexes")
(println " {")
(doseq [key (-> rel :indexes keys)]
(println " " key)
(println " {")
(doseq [val (keys ((:indexes rel) key))]
(println " " val)
(println " " (get-in rel [:indexes key val])))
(println " }"))
(println " })"))))
(defn datalog-relation
"Creates a relation"
[schema data indexes]
(with-meta (struct relation schema data indexes) {:type ::datalog-relation}))
(defn add-relation
"Adds a relation to the database"
[db name keys]
(assoc db name (datalog-relation (set keys) #{} {})))
(defn add-index
"Adds an index to an empty relation named name"
[db name key]
(assert (empty? (:data (db name))))
(let [rel (db name)
inx (assoc (:indexes rel) key {})]
(assoc db name (datalog-relation (:schema rel)
(:data rel)
(defn ensure-relation
"If the database lacks the named relation, add it"
[db name keys indexes]
(if-let [rel (db name)]
(assert (= (:schema rel) (set keys)))
(let [db1 (add-relation db name keys)]
(reduce (fn [db key] (add-index db name key))
(defmacro make-database
"Makes a database, like this
(relation :fred [:mary :sue])
(index :fred :mary)
(relation :sally [:jen :becky])
(index :sally :jen)
(index :sally :becky))"
[& commands]
(let [wrapper (fn [cur new]
(let [cmd (first new)
body (next new)]
(assert (= 2 (count body)))
(= cmd 'relation)
`(add-relation ~cur ~(first body) ~(fnext body))
(= cmd 'index)
`(add-index ~cur ~(first body) ~(fnext body))
:otherwise (throwf "%s not recognized" new))))]
(reduce wrapper `empty-database commands)))
(defn get-relation
"Get a relation object by name"
[db rel-name]
(db rel-name))
(defn replace-relation
"Add or replace a fully constructed relation object to the database."
[db rel-name rel]
(assoc db rel-name rel))
;;; DML
(defn database-counts
"Returns a map with the count of elements in each relation."
(map-values #(-> % :data count) db))
(defn- modify-indexes
"Perform f on the indexed tuple-set. f should take a set and tuple,
and return the new set."
[idxs tuple f]
(into {} (for [ik (keys idxs)]
(let [im (idxs ik)
iv (tuple ik)
os (get im iv #{})
ns (f os tuple)]
[ik (if (empty? ns)
(dissoc im iv)
(assoc im iv (f os tuple)))]))))
(defn- add-to-indexes
"Adds the tuple to the appropriate keys in the index map"
[idxs tuple]
(modify-indexes idxs tuple conj))
(defn- remove-from-indexes
"Removes the tuple from the appropriate keys in the index map"
[idxs tuple]
(modify-indexes idxs tuple disj))
(defn add-tuple
"Two forms:
[db relation-name tuple] adds tuple to the named relation. Returns
the new database.
[rel tuple] adds to the relation object. Returns the new relation."
([db rel-name tuple]
(assert (= (-> tuple keys set) (-> rel-name db :schema)))
(assoc db rel-name (add-tuple (db rel-name) tuple)))
([rel tuple]
(let [data (:data rel)
new-data (conj data tuple)]
(if (identical? data new-data) ; optimization hack!
(let [idxs (add-to-indexes (:indexes rel) tuple)]
(assoc rel :data new-data :indexes idxs))))))
(defn remove-tuple
"Two forms:
[db relation-name tuple] removes the tuple from the named relation,
returns a new database.
[rel tuple] removes the tuple from the relation. Returns the new
([db rel-name tuple] (assoc db rel-name (remove-tuple (db rel-name) tuple)))
([rel tuple]
(let [data (:data rel)
new-data (disj data tuple)]
(if (identical? data new-data)
(let [idxs (remove-from-indexes (:indexes rel) tuple)]
(assoc rel :data new-data :indexes idxs))))))
(defn add-tuples
"Adds a collection of tuples to the db, as
(add-tuples db
[:rel-name :key-1 1 :key-2 2]
[:rel-name :key-1 2 :key-2 3])"
[db & tupls]
(reduce #(add-tuple %1 (first %2) (apply hash-map (next %2))) db tupls))
(defn- find-indexes
"Given a map of indexes and a partial tuple, return the sets of full tuples"
[idxs pt]
(if (empty? idxs)
(filter identity (for [key (keys pt)]
(if-let [idx-map (idxs key)]
(get idx-map (pt key) #{})
(defn- match?
"Is m2 contained in m1?"
[m1 m2]
(let [compare (fn [key]
(and (contains? m1 key)
(= (m1 key) (m2 key))))]
(every? compare (keys m2))))
(defn- scan-space
"Computes a stream of tuples from relation rn matching partial tuple (pt)
and applies fun to each"
[fun db rn pt]
(let [rel (db rn)
idxs (find-indexes (:indexes rel) pt)
space (if (empty? idxs)
(:data rel) ; table scan :(
(reduce intersection idxs))]
(trace-datalog (when (empty? idxs)
(println (format "Table scan of %s: %s rows!!!!!"
(count space)))))
(fun #(match? % pt) space)))
(defn select
"finds all matching tuples to the partial tuple (pt) in the relation named (rn)"
[db rn pt]
(scan-space filter db rn pt))
(defn any-match?
"Finds if there are any matching records for the partial tuple"
[db rn pt]
(if (= (-> pt keys set) (:schema (db rn)))
(contains? (:data (db rn)) pt)
(scan-space some db rn pt)))
;;; Merge
(defn merge-indexes
[idx1 idx2]
(merge-with (fn [h1 h2] (merge-with union h1 h2)) idx1 idx2))
(defn merge-relations
"Merges two relations"
[r1 r2]
(assert (= (:schema r1) (:schema r2)))
(let [merged-indexes (merge-indexes (:indexes r1)
(:indexes r2))
merged-data (union (:data r1)
(:data r2))]
(assoc r1 :data merged-data :indexes merged-indexes)))
(defn database-merge
"Merges databases together"
(apply merge-with merge-relations dbs))
(defn database-merge-parallel
"Merges databases together in parallel"
(preduce merge-relations dbs))
;; End of file
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