Module type Datalog.S

module type S = sig .. end


Literals and clauses


type symbol 
Abstract type of symbols (individual objects)
type term = private 
| Var of int
| Const of symbol (*Individual object*)
val mk_var : int -> term
val mk_const : symbol -> term
type literal 
A datalog atom, i.e. pred(arg_1, ..., arg_n). The first element of the array is the predicate, then arguments follow
type clause 
A datalog clause, i.e. head :- body_1, ..., body_n
type soft_lit = symbol * term list 
type soft_clause = soft_lit * soft_lit list 

Constructors and destructors


val mk_literal : symbol -> term list -> literal
Helper to build a literal. Arguments are either variables or constants
val of_soft_lit : soft_lit -> literal
val open_literal : literal -> soft_lit
Deconstruct a literal
val mk_clause : literal -> literal list -> clause
Create a clause from a conclusion and a list of premises
val of_soft_clause : soft_clause -> clause
val open_clause : clause -> soft_clause
Deconstruct a clause
val is_ground : literal -> bool
Is the literal ground (a fact)?
val arity : literal -> int
Number of subliterals of the literal. Ex for p(a,b,c) it returns 3

Comparisons


val eq_term : term -> term -> bool
val eq_literal : literal -> literal -> bool
Are the literals equal?
val hash_literal : literal -> int
Hash the literal
val check_safe : clause -> bool
A datalog clause is safe iff all variables in its head also occur in its body
val is_fact : clause -> bool
A fact is a ground clause with empty body
val eq_clause : clause -> clause -> bool
Check whether clauses are (syntactically) equal
val hash_clause : clause -> int
Hash the clause

Pretty-printing


val pp_term : Format.formatter -> term -> unit
val pp_literal : Format.formatter -> literal -> unit
Pretty print the literal
val pp_clause : Format.formatter -> clause -> unit
Pretty print the clause

The Datalog unit resolution algorithm


exception UnsafeClause
type db 
A database of facts and clauses, with incremental fixpoint computation
type explanation = 
| Axiom
| Resolution of clause * literal
| ExtExplanation of string * Datalog.Univ.t (*Explanation for a clause or fact. It is extensible through universal types.*)
val db_create : unit -> db
Create a DB
val db_copy : db -> db
Deep copy of the DB
val db_mem : db -> clause -> bool
Is the clause member of the DB?
val db_add : ?expl:explanation -> db -> clause -> unit
Add the clause/fact to the DB as an axiom, updating fixpoint. UnsafeRule will be raised if the rule is not safe (see Datalog.S.check_safe)
val db_add_fact : ?expl:explanation -> db -> literal -> unit
Add a fact (ground unit clause)
val db_goal : db -> literal -> unit
Add a goal to the DB. The goal is used to trigger backward chaining (calling goal handlers that could help solve the goal)
val db_match : db -> literal -> (literal -> unit) -> unit
match the given literal with facts of the DB, calling the handler on each fact that match
val db_query : db ->
literal -> int list -> (symbol list -> unit) -> unit
Like Datalog.S.db_match, but the additional int list is used to select bindings of variables in the literal. Their bindings, in the same order, are given to the callback.
val db_size : db -> int
Size of the DB
val db_fold : ('a -> clause -> 'a) -> 'a -> db -> 'a
Fold on all clauses in the current DB (including fixpoint)
type fact_handler = literal -> unit 
type goal_handler = literal -> unit 
val db_subscribe_fact : db -> symbol -> fact_handler -> unit
val db_subscribe_all_facts : db -> fact_handler -> unit
val db_subscribe_goal : db -> goal_handler -> unit
type user_fun = soft_lit -> soft_lit 
val db_add_fun : db -> symbol -> user_fun -> unit
Add a function to be called on new literals. Only one function per symbol can be registered.
val db_goals : db -> (literal -> unit) -> unit
Iterate on all current goals
val db_explain : db -> literal -> literal list
Explain the given fact by returning a list of facts that imply it under the current clauses, or raise Not_found
val db_premises : db ->
literal -> clause * literal list
Immediate premises of the fact (ie the facts that resolved with a clause to give the literal), plus the clause that has been used.
val db_explanations : db -> clause -> explanation list
Get all the explanations that explain why this clause is true

Querying


module Query: sig .. end