type fruit = int
table fruit : { Id : fruit, Nam : string, Weight : float, Secret : string }
PRIMARY KEY Id,
CONSTRAINT Nam UNIQUE Nam
type order = int
table order : { Id : order, Fruit : fruit, Qty : int, Code : int }
PRIMARY KEY Id,
CONSTRAINT Fruit FOREIGN KEY Fruit REFERENCES fruit(Id)
(* Everyone may knows IDs and names. *)
policy query_policy (SELECT fruit.Id, fruit.Nam
FROM fruit)
(* The weight is sensitive information; you must know the secret. *)
policy query_policy (SELECT fruit.Weight
FROM fruit
WHERE known(fruit.Secret))
policy query_policy (SELECT order.Id, order.Fruit, order.Qty
FROM order, fruit
WHERE order.Fruit = fruit.Id
AND order.Qty = 13)
fun fname r =
x <- queryX (SELECT fruit.Weight
FROM fruit
WHERE fruit.Nam = {[r.Nam]}
AND fruit.Secret = {[r.Secret]})
(fn r => Weight is {[r.Fruit.Weight]});
return
{x}
fun main () =
x1 <- queryX (SELECT fruit.Id, fruit.Nam
FROM fruit)
(fn x => {[x.Fruit.Id]}: {[x.Fruit.Nam]});
x2 <- queryX (SELECT fruit.Nam, order.Qty
FROM fruit, order
WHERE fruit.Id = order.Fruit
AND order.Qty = 13)
(fn x => {[x.Fruit.Nam]}: {[x.Order.Qty]});
return