diff --git a/src/Data/Event.purs b/src/Data/Event.purs
index b62a004..f03ff39 100644
--- a/src/Data/Event.purs
+++ b/src/Data/Event.purs
@@ -1,6 +1,5 @@
 module Data.Event
   ( Event(..)
-  , EventType(..)
   , SourceID
   , SessionID
   , DestinationID
@@ -9,6 +8,7 @@ module Data.Event
   , FeatureID
   , InstanceID
   , module Data.Event.Class
+  , module Data.Event.EventType
   , eventTypes
   , foreignEvent
   ) where
@@ -25,7 +25,7 @@ import FFI.UUID (UUID)
 
 import Data.Event.Class (class EventCategory, class EventID, eventCategories, eventIDs)
 
-data EventType = Success | Failure
+import Data.Event.EventType (EventType(..))
 
 type SourceID      = UUID
 type SessionID     = UUID
@@ -52,20 +52,43 @@ data Event a b = Event (EventCategory a => EventID b =>
   , endTime       :: Date
   }) 
 
-instance showEventType :: Show EventType where
-  show Success = "SUCCESS"
-  show Failure = "FAILURE"
+{-- todo: see https://github.com/markfarrell/3iter/issues/5 --}
+
+type Feature a b = (EventCategory a => EventID b =>
+  { eventCategory :: a 
+  , eventType     :: EventType
+  , eventID       :: b
+  })
+
+type Identifier =
+  { sourceID      :: SourceID
+  , sessionID     :: SessionID
+  , destinationID :: DestinationID
+  , logID         :: LogID
+  , schemaID      :: SchemaID
+  }
+
+type Checksum =
+  { featureID  :: FeatureID
+  , instanceID :: InstanceID
+  }
+
+type Period =
+  { startTime :: Date
+  , duration  :: Int
+  , endTime   :: Date 
+  }
 
 instance showEvent :: (EventCategory a, EventID b) => Show (Event a b) where
   show = JSON.stringify <<< foreignEvent
 
-derive instance eqEventType :: Eq EventType
-
 derive instance eqEvent :: (EventCategory a, EventID b) => Eq (Event a b)
 
 eventTypes :: Array EventType
 eventTypes = [ Success, Failure ]
 
+{-- todo: see https://github.com/markfarrell/3tier/issues/27 --}
+
 foreignEvent :: forall a b. EventCategory a => EventID b => Event a b -> Foreign
 foreignEvent (Event x) = unsafeCoerce $
   { eventCategory : show x.eventCategory
diff --git a/src/Data/Event/EventType.purs b/src/Data/Event/EventType.purs
new file mode 100644
index 0000000..31efaba
--- /dev/null
+++ b/src/Data/Event/EventType.purs
@@ -0,0 +1,15 @@
+module Data.Event.EventType
+  ( EventType (..)
+  ) where
+
+import Prelude
+
+{-- todo: see https://github.com/markfarrell/3tier/issues/5 --}
+
+data EventType = Success | Failure
+
+instance showEventType :: Show EventType where
+  show Success = "SUCCESS"
+  show Failure = "FAILURE"
+
+derive instance eqEventType :: Eq EventType
diff --git a/src/Data/Forward.purs b/src/Data/Forward.purs
index 12cddfd..8778cd9 100644
--- a/src/Data/Forward.purs
+++ b/src/Data/Forward.purs
@@ -11,10 +11,10 @@ import Data.Linux   as Linux
 import Data.Windows as Windows
 
 data Event = 
-    Alert Alert.Event
-  | Audit Audit.Event 
+    Alert   Alert.Event
+  | Audit   Audit.Event 
   | Traffic Traffic.Event
-  | Linux Linux.Event
+  | Linux   Linux.Event
   | Windows Windows.Event
 
 instance showEventForward :: Show Event where