A view can be delta predicates with --prepare option.

bin/dl2u.ml

@@ -11,7 +11,7 @@ let sort rules =
 
 let simplify rules sources =
   let open Result in
-  match Simplification.simplify rules sources with
+  match Simplification.simplify rules None sources with
   | Error err ->
       error @@ Simplification.string_of_error err
   | Result.Ok rules ->

bin/simplification.ml

@@ -1,5 +1,11 @@
 open Birds
 
+let build_view ast =
+  if Array.length Sys.argv >= 3 && Sys.argv.(2) = "--prepare" then
+    ast.Expr.view
+  else
+    None
+
 let _ =
   if Array.length Sys.argv < 2 then
     print_endline "Invalid arguments. File name must be passed."
@@ -10,11 +16,12 @@ let _ =
     let ast = Parser.main Lexer.token lexbuf in
     let rules = ast.rules in
     let sources = ast.sources in
+    let view = build_view ast in
     match Inlining.sort_rules rules with
     | Result.Error err ->
       print_endline @@ Inlining.string_of_error err
     | Result.Ok rules ->
-      match Simplification.simplify rules sources with
+      match Simplification.simplify rules view sources with
       | Result.Error err ->
         print_endline @@ Simplification.string_of_error err
       | Result.Ok rules ->

examples/simplification_prepare1.dl

@@ -0,0 +1,5 @@
+source x('A':int).
+view v('A':int).
+
++x(A) :- x(A), v(A), A <> 42.
+-x(A) :- +x(A), -v(A).

src/simplification.ml

@@ -585,7 +585,7 @@ let rec simplify_rule_recursively (imrule1 : intermediate_rule) : intermediate_r
     simplify_rule_recursively imrule2
 
 
-let resolve_undefined_predicates (imrules : intermediate_rule list) : intermediate_rule list =
+let resolve_undefined_predicates (view : PredicateSet.t) (imrules : intermediate_rule list) : intermediate_rule list =
   imrules
   |> List.fold_left (fun (preds_set, acc) imrule ->
     let { head_predicate; positive_terms; negative_terms; _ } = imrule in
@@ -620,15 +620,15 @@ let resolve_undefined_predicates (imrules : intermediate_rule list) : intermedia
         let preds_set = preds_set |> PredicateSet.add head_predicate in
         let imrule = { imrule with positive_terms; negative_terms } in
         (preds_set, imrule :: acc)
-  ) (PredicateSet.empty, [])
+  ) (view, [])
   |> snd
   |> List.rev
 
 
 module TableNameSet = Set.Make(String)
 
 
-let remove_unused_rules (sources : TableNameSet.t) (imrules : intermediate_rule list) : intermediate_rule list =
+let remove_unused_rules (sources : TableNameSet.t) (view : PredicateSet.t) (imrules : intermediate_rule list) : intermediate_rule list =
   List.fold_right (fun imrule (pred_set, acc) ->
     let { positive_terms; negative_terms; _ } = imrule in
     let terms = PredicateMap.union (fun _ x _ -> Some x) positive_terms negative_terms in
@@ -657,7 +657,7 @@ let remove_unused_rules (sources : TableNameSet.t) (imrules : intermediate_rule
         else
           (pred_set, acc)
 
-  ) imrules (PredicateSet.empty, [])
+  ) imrules (view, [])
   |> snd
 
 
@@ -781,7 +781,7 @@ let remove_duplicate_rules (rules : rule list) : rule list =
   with
   | (rules, _) -> rules
 
-let simplify (rules : rule list) (sources : source list) : (rule list, error) result =
+let simplify (rules : rule list) (view : view option) (sources : source list) : (rule list, error) result =
   let open ResultMonad in
 
   (* Converts each rule to an intermediate rule (with unsatisfiable ones removed): *)
@@ -794,8 +794,14 @@ let simplify (rules : rule list) (sources : source list) : (rule list, error) re
   (* Performs per-rule simplification: *)
   let imrules = imrules |> List.map simplify_rule_recursively in
 
+  let view =
+    match view with
+    | None      -> PredicateSet.empty
+    | Some (view, _) -> PredicateSet.of_list [ImDeltaInsert view; ImDeltaDelete view]
+  in
+
   (* Removes predicates that are not defined: *)
-  let imrules = imrules |> resolve_undefined_predicates in
+  let imrules = imrules |> resolve_undefined_predicates view in
 
   let sources =
     sources
@@ -804,7 +810,7 @@ let simplify (rules : rule list) (sources : source list) : (rule list, error) re
   in
 
   (* Removes rules that are not used: *)
-  let imrules = imrules |> remove_unused_rules sources in
+  let imrules = imrules |> remove_unused_rules sources view in
 
   (* Removes rules that have a contradicting body: *)
   let imrules = imrules |> List.filter (fun imrule -> not (has_contradicting_body imrule)) in

src/simplification.mli

@@ -3,6 +3,6 @@ open Expr
 
 type error
 
-val simplify : rule list -> source list -> (rule list, error) result
+val simplify : rule list -> view option -> source list -> (rule list, error) result
 
 val string_of_error : error -> string

test/ast2sql_operation_based_conversion_test.ml

@@ -210,7 +210,7 @@ let main () =
                   assert false
               | Ok rules ->
                 let sources = [ "a", []; "b", []; "v", [] ] in
-                match Simplification.simplify rules sources with
+                match Simplification.simplify rules None sources with
                 | Error err ->
                     Printf.printf "Error: %s\n" (Simplification.string_of_error err);
                     assert false

test/simplification_test.ml

@@ -5,7 +5,7 @@ open Expr
 
 type test_case = {
   title    : string;
-  input    : rule list * source list;
+  input    : rule list * view option * source list;
   expected : rule list;
 }
 
@@ -16,12 +16,12 @@ type test_result =
 
 let run_test (test_case : test_case) =
   let open ResultMonad in
-  let rules, sources = test_case.input in
+  let rules, view, sources = test_case.input in
   match Inlining.sort_rules rules with
   | Error err ->
       return (Fail { expected = "no error when sorting rules."; got = Inlining.string_of_error err })
   | Ok rules ->
-    Simplification.simplify rules sources >>= fun got ->
+    Simplification.simplify rules view sources >>= fun got ->
     let s_got = got |> List.map string_of_rule |> String.concat "; " in
     let s_expected = test_case.expected |> List.map string_of_rule |> String.concat "; " in
     if String.equal s_got s_expected then
@@ -61,7 +61,7 @@ let main () =
   run_tests [
     {
       title    = "empty";
-      input    = [], [];
+      input    = [], None, [];
       expected = [];
     };
     {
@@ -82,6 +82,7 @@ let main () =
           Equat (Equation ("=", Var rating, Const (Int 1)));
         ]);
       ],
+      None,
       [ "tracks", [] ];
       expected = [
         (* (1) simplified:
@@ -118,6 +119,7 @@ let main () =
           Not (Pred ("tracks", [ NamedVar "V31"; NamedVar "V32"; NamedVar "V33"; album ]));
         ]);
       ],
+      None,
       [ "tracks", [] ];
       expected = [];
     };
@@ -139,6 +141,7 @@ let main () =
           Equat (Equation ("=", Var (NamedVar "V6855"), Const (Int 1)));
         ]);
       ],
+      None,
       [ "albums", [] ];
       expected = [
         (* (7) simplified:
@@ -173,6 +176,7 @@ let main () =
           Noneq (Equation ("=", Var rating, Const (Int 1)));
         ]);
       ],
+      None,
       [ "albums", [] ];
       expected = [
         (* (32) simplified:
@@ -209,6 +213,7 @@ let main () =
           Not (Pred ("eed", [NamedVar "E"; NamedVar "D"]));
         ]);
       ],
+      None,
       [ "eed", []; "ed", [] ];
       expected = [
         (* Boolean body simplified:
@@ -257,6 +262,7 @@ let main () =
         (Pred ("g", [NamedVar "X"]), [Equat (Equation ("=", (Var (NamedVar "X")), (Const (Int 1))))]);
         (Pred ("f", [NamedVar "X"]), [Equat (Equation ("=", (Var (NamedVar "X")), (Const (Int 1))))]);
       ],
+      None,
       [ "f", []; "g", []; "a", []; "b", []; "c", []; "d", [] ];
       expected = [
         (Deltadelete ("g", [NamedVar "X"]), [Rel (Pred ("g", [NamedVar "X"]))]);
@@ -309,6 +315,7 @@ let main () =
           ]);
           (Pred ("v", [NamedVar "A"]), [Rel (Pred ("s", [NamedVar "A"; NamedVar "B"]))]);
       ],
+      None,
       [ "v", []; "s", [] ];
       expected = [
         (Deltainsert ("s", [NamedVar "A"; NamedVar "B"]), [
@@ -394,6 +401,7 @@ let main () =
           (Equat (Equation ("<>", Var (NamedVar "A"), Const (Int 4))));
         ]);
       ],
+      None,
       ["ps", []];
       expected = [
         (*
@@ -507,6 +515,7 @@ let main () =
           Not (Pred ("__updated__v", [NamedVar "A"; NamedVar "B"; NamedVar "GENV1"]))
         ]);
       ],
+      None,
       ["a", []; "b", []];
       expected = [
         (*