Datalog规则和Datomic规则是否等效

Question

我有一个简单的Datalog程序，我试图在Datomic中使用Closure表达。这个想法是可以选择assertions，选择一些断言也可以选择其他断言。这是Datalog程序：

% Facts
assertion("id1", "1").
assertion("id11", "1.1").
assertion("id2", "2").
assertion("id3", "3").

select_assertion("id1").

% Rules:
selected(Id, Name) :- assertion(Id, Name), select_assertion(Id).

select_assertion(IdChild) :-
  assertion(IdChild, "1.1"),
  assertion(IdParent, "1"),
  select_assertion(IdParent).

运行查询：

selected(A,B)?
=>
selected(id1, 1).
selected(id11, "1.1").

选择“1”，也选择“1.1”。我一直试图在Datomic中表达这一点，但发现很难让rules看起来和facts一样，这样查询就可以区分它们。这是我所拥有的：

% ... connection stuff

(def schema [{:db/ident :assertion/name
              :db/valueType :db.type/string
              :db/cardinality :db.cardinality/one
              :db/doc "The name of an assertion"}

             {:db/ident :select_assertion/assertion
              :db/valueType :db.type/ref
              :db/cardinality :db.cardinality/one
              :db/doc "The ID of an assertion to be selected"}
             ])

(def data [
           {:db/id "id-1" :assertion/name "1"}
           {:assertion/name "1.1"}
           {:assertion/name "2"}
           {:assertion/name "3"}
           {:select_assertion/assertion "id-1"}
           ])

(def rules '[
             [(selected ?assertion_name)
              [?a :assertion/name ?assertion_name]
              [_ :select_assertion/assertion ?a]]

             [(select_assertion "1.1")
              [?a :assertion/name "1"]
              [_ :select_assertion/assertion ?a]]])

(def selected '[:find ?c
                :in $ %
                :where
                (selected ?c)])

(defn reload-dbs []
  (d/transact conn {:tx-data schema})
  (d/transact conn {:tx-data data}))

(defn query []
  (d/q selected db rules))

如何在不诉诸析取的情况下使Datomic查询返回相同的内容？

Answer 1

虽然我无法回答“他们是否相同”的问题，但在观看https://www.youtube.com/watch?v=bAilFQdaiHk&feature=youtu.be&t=464之后我能够得到类似的效果。它指出具有相同名称的多个规则与隐式OR组合。这看起来类似于Datalog。

将代码切换为：

(def rules '[
             [(selected ?a)
              [?a :assertion/name ?assertion_name]
              [_ :select_assertion/assertion ?a]]
             [(selected ?a)
              [?a  :assertion/name "1.1"]
              [?ap :assertion/name "1"]
              [_ :select_assertion/assertion ?ap]]])

(def selected '[:find ?a ?n
                :in $ %
                :where
                (selected ?a)
                [?a :assertion/name ?n]])

给出正确的答案。这里第一个selected返回具有名称的实体的ID，并且也被选中。第二个selected返回实体的ID，如果它具有名称“1.1”并且还有另一个实体具有名称“1”并且也被选中。

我认为我的困惑围绕着entity的想法。在Datomic中，您可以拥有一个具有任何属性组合的实体。然而，在Datalog他们有atoms，其名称是predicate。在Datomic中，您可以通过创建返回所需属性的规则来获得与这些predicates相同的效果。