module type STORAGE = sig
  type connection
  type transaction

  val connect : Concepts.Configuration.term -> (connection, Concepts.Condition.condition) result

  (** begin a transaction within `connection` *)
  val start : connection -> (transaction, Concepts.Condition.condition) result

  (** `commit` the current transaction *)
  val commit : transaction -> (unit, Concepts.Condition.condition) result

  (** `abort` the current transaction *)
  val abort : transaction -> (unit, Concepts.Condition.condition) result

  (** within a transaction, fetch a blob from disk *)
  val get :
    transaction ->
    Concepts.Hash.hash ->
    (Concepts.Representation.blob option, Concepts.Condition.condition) result

  (** within a transaction, associate a hash with a blob on disk *)
  val put :
    transaction ->
    Concepts.Hash.hash ->
    Concepts.Representation.blob ->
    (unit, Concepts.Condition.condition) result
end