diff --git a/infer/src/quandary/Passthrough.ml b/infer/src/quandary/Passthrough.ml
new file mode 100644
index 000000000..2ffbc0dba
--- /dev/null
+++ b/infer/src/quandary/Passthrough.ml
@@ -0,0 +1,36 @@
+(*
+ * Copyright (c) 2016 - present Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *)
+
+open! Utils
+
+module F = Format
+
+(* for now this is just a call site, but in the future we may add input access path, output kind,
+   etc. depending on what we need *)
+type t =
+  {
+    site : CallSite.t;
+  }
+
+let make site =
+  { site }
+
+let compare pt1 pt2 =
+  (match pt1, pt2 with
+   | {site=site1}, {site=site2} -> CallSite.compare site1 site2
+  )[@warning "+9"]
+
+let pp fmt s =
+  F.fprintf fmt "%a" CallSite.pp s.site
+
+module Set = PrettyPrintable.MakePPSet(struct
+    type nonrec t = t
+    let compare = compare
+    let pp_element = pp
+  end)
diff --git a/infer/src/quandary/Passthrough.mli b/infer/src/quandary/Passthrough.mli
new file mode 100644
index 000000000..0dfe560ef
--- /dev/null
+++ b/infer/src/quandary/Passthrough.mli
@@ -0,0 +1,20 @@
+(*
+ * Copyright (c) 2016 - present Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *)
+
+module F = Format
+
+type t
+
+val make : CallSite.t -> t
+
+val compare : t -> t -> int
+
+val pp : F.formatter -> t -> unit
+
+module Set : PrettyPrintable.PPSet with type elt = t
diff --git a/infer/src/quandary/Sink.ml b/infer/src/quandary/Sink.ml
new file mode 100644
index 000000000..591f0ae88
--- /dev/null
+++ b/infer/src/quandary/Sink.ml
@@ -0,0 +1,16 @@
+(*
+ * Copyright (c) 2016 - present Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *)
+
+module type S = sig
+  include TraceElem.S
+
+  val to_callee : t -> CallSite.t -> t
+  (** ith param * ith source kind *)
+  val get : CallSite.t -> (int * t) list
+end
diff --git a/infer/src/quandary/Source.ml b/infer/src/quandary/Source.ml
new file mode 100644
index 000000000..0eb2fbf66
--- /dev/null
+++ b/infer/src/quandary/Source.ml
@@ -0,0 +1,19 @@
+(*
+ * Copyright (c) 2016 - present Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *)
+
+module type S = sig
+  include TraceElem.S
+
+  val is_footprint : t -> bool
+  val to_return : t -> CallSite.t -> t
+  val make_footprint : CallSite.t -> t
+
+  (** ith return value * ith sink kind *)
+  val get : CallSite.t -> (int * t) list
+end
diff --git a/infer/src/quandary/TraceElem.ml b/infer/src/quandary/TraceElem.ml
new file mode 100644
index 000000000..233a253b1
--- /dev/null
+++ b/infer/src/quandary/TraceElem.ml
@@ -0,0 +1,26 @@
+(*
+ * Copyright (c) 2016 - present Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *)
+
+module F = Format
+
+module type S = sig
+  type kind
+  type t
+
+  val call_site : t -> CallSite.t
+  val kind : t -> kind
+  val is_empty : t -> bool
+
+  val make : kind -> CallSite.t -> t
+  val make_empty : CallSite.t -> t
+
+  val compare : t -> t -> int
+  val equal : t -> t -> bool
+  val pp : F.formatter -> t -> unit
+end