diff --git a/SciFlow.cabal b/SciFlow.cabal
--- a/SciFlow.cabal
+++ b/SciFlow.cabal
@@ -1,5 +1,5 @@
 name:                SciFlow
-version:             0.6.0
+version:             0.6.1
 synopsis:            Scientific workflow management system
 description:         SciFlow is a DSL for building scientific workflows.
                      Workflows built with SciFlow can be run either on desktop
@@ -58,7 +58,7 @@
     , lifted-async
     , mtl
     , network
-    , optparse-applicative >=0.13.0.0
+    , optparse-applicative >=0.14.0.0
     , rainbow
     , sqlite-simple
     , split
diff --git a/src/Scientific/Workflow/Internal/Builder.hs b/src/Scientific/Workflow/Internal/Builder.hs
--- a/src/Scientific/Workflow/Internal/Builder.hs
+++ b/src/Scientific/Workflow/Internal/Builder.hs
@@ -162,8 +162,9 @@
 -- | Add a prefix to IDs of nodes for a given builder, i.e.,
 -- @id@ becomes @prefix_id@.
 namespace :: T.Text -> Builder () -> Builder ()
-namespace prefix builder = builder >> addPrefix
+namespace prefix builder = modify (st <>)
   where
+    st = execState (builder >> addPrefix) ([], [])
     addPrefix = modify $ \(nodes, edges) ->
         ( map (\x -> x{_nodePid = prefix <> "_" <> _nodePid x}) nodes
         , map (\x -> x{ _edgeFrom = prefix <> "_" <> _edgeFrom x
@@ -300,7 +301,7 @@
         (Fail ex) -> liftIO (putMVar pSt pStValue) >> lift (throwE (pid, ex))
         Success -> liftIO $ do
             putMVar pSt pStValue
-            readData pid $ wfState^.database
+            fmap deserialize $ readData pid $ wfState^.database
         Scheduled -> do
             _ <- liftIO $ takeMVar $ wfState^.procParaControl
 
@@ -324,7 +325,7 @@
                         sendLog (wfState^.logServer) $ Warn pid "Failed!"
                     lift (throwE (pid, ex))
                 Right r -> liftIO $ do
-                    saveData pid r $ wfState^.database
+                    saveData pid (serialize r) $ wfState^.database
                     putMVar pSt Success
                     _ <- forkIO $ putMVar (wfState^.procParaControl) ()
                     sendLog (wfState^.logServer) $ Complete pid
@@ -351,7 +352,7 @@
 
     -- Read data stored in this node
     FetchData -> liftIO $ do
-        r <- readData pid $ wfState^.database
+        r <- fmap deserialize $ readData pid $ wfState^.database
         B.putStr $ showYaml r
         putMVar nodeSt $ Special Skip
         return r
@@ -361,7 +362,7 @@
         c <- liftIO $ B.readFile inputData
         r <- return (readYaml c) `asTypeOf` fn undefined
         liftIO $ do
-            updateData pid r $ wfState^.database
+            updateData pid (serialize r) $ wfState^.database
             putMVar nodeSt $ Special Skip
             return r
 {-# INLINE handleSpecialMode #-}
diff --git a/src/Scientific/Workflow/Internal/Builder/Types.hs b/src/Scientific/Workflow/Internal/Builder/Types.hs
--- a/src/Scientific/Workflow/Internal/Builder/Types.hs
+++ b/src/Scientific/Workflow/Internal/Builder/Types.hs
@@ -73,7 +73,7 @@
 deriveLift ''FunctionType
 deriveLift ''Attribute
 
-makeLenses 'Attribute
+makeLenses ''Attribute
 
 defaultAttribute :: Attribute
 defaultAttribute = Attribute
diff --git a/src/Scientific/Workflow/Internal/DB.hs b/src/Scientific/Workflow/Internal/DB.hs
--- a/src/Scientific/Workflow/Internal/DB.hs
+++ b/src/Scientific/Workflow/Internal/DB.hs
@@ -1,13 +1,11 @@
+{-# LANGUAGE ConstraintKinds      #-}
 {-# LANGUAGE FlexibleInstances    #-}
 {-# LANGUAGE OverloadedStrings    #-}
 {-# LANGUAGE UndecidableInstances #-}
-{-# LANGUAGE ConstraintKinds #-}
 module Scientific.Workflow.Internal.DB
     ( openDB
     , closeDB
     , readData
-    , readDataByteString
-    , saveDataByteString
     , saveData
     , updateData
     , delRecord
@@ -30,8 +28,9 @@
 import           Database.SQLite.Simple
 import           Text.Printf            (printf)
 
--- | An abstract type representing the database used to store states of workflow
-newtype WorkflowDB  = WorkflowDB Connection
+--------------------------------------------------------------------------------
+-- Data Serialization
+--------------------------------------------------------------------------------
 
 -- | @DBData@ constraint is used for data serialization.
 type DBData a = (FromJSON a, ToJSON a, S.Serialize a)
@@ -51,8 +50,13 @@
 readYaml :: DBData a => B.ByteString -> a
 readYaml = fromJust . decode
 
-type PID = T.Text
 
+-- | An abstract type representing the database used to store states of workflow
+newtype WorkflowDB  = WorkflowDB Connection
+type Key = T.Text
+type Val = B.ByteString
+
+
 dbTableName :: String
 dbTableName = "SciFlowDB"
 
@@ -82,48 +86,36 @@
 closeDB (WorkflowDB db) = close db
 {-# INLINE closeDB #-}
 
-readData :: DBData r => PID -> WorkflowDB -> IO r
+readData :: Key -> WorkflowDB -> IO Val
 readData pid (WorkflowDB db) = do
     [Only result] <- query db (Query $ T.pack $
         printf "SELECT data FROM %s WHERE pid=?" dbTableName) [pid]
-    return $ deserialize result
-{-# INLINE readData #-}
-
-readDataByteString :: PID -> WorkflowDB -> IO B.ByteString
-readDataByteString pid (WorkflowDB db) = do
-    [Only result] <- query db (Query $ T.pack $
-        printf "SELECT data FROM %s WHERE pid=?" dbTableName) [pid]
     return result
-{-# INLINE readDataByteString #-}
-
-saveData :: DBData r => PID -> r -> WorkflowDB -> IO ()
-saveData pid result (WorkflowDB db) = execute db (Query $ T.pack $
-    printf "INSERT INTO %s VALUES (?, ?)" dbTableName) (pid, serialize result)
-{-# INLINE saveData #-}
+{-# INLINE readData #-}
 
-updateData :: DBData r => PID -> r -> WorkflowDB -> IO ()
+updateData :: Key -> Val -> WorkflowDB -> IO ()
 updateData pid result (WorkflowDB db) = execute db (Query $ T.pack $
-    printf "UPDATE %s SET data=? WHERE pid=?" dbTableName) (serialize result, pid)
+    printf "UPDATE %s SET data=? WHERE pid=?" dbTableName) (result, pid)
 {-# INLINE updateData #-}
 
-saveDataByteString :: PID -> B.ByteString -> WorkflowDB -> IO ()
-saveDataByteString pid result (WorkflowDB db) = execute db (Query $ T.pack $
+saveData :: Key -> Val -> WorkflowDB -> IO ()
+saveData pid result (WorkflowDB db) = execute db (Query $ T.pack $
     printf "INSERT INTO %s VALUES (?, ?)" dbTableName) (pid, result)
-{-# INLINE saveDataByteString #-}
+{-# INLINE saveData #-}
 
-isFinished :: PID -> WorkflowDB -> IO Bool
+isFinished :: Key -> WorkflowDB -> IO Bool
 isFinished pid (WorkflowDB db) = do
     result <- query db (Query $ T.pack $
         printf "SELECT pid FROM %s WHERE pid = ?" dbTableName) [pid]
     return $ not $ null (result :: [Only T.Text])
 {-# INLINE isFinished #-}
 
-getKeys :: WorkflowDB -> IO [PID]
+getKeys :: WorkflowDB -> IO [Key]
 getKeys (WorkflowDB db) = concat <$> query_ db (Query $ T.pack $
     printf "SELECT pid FROM %s;" dbTableName)
 {-# INLINE getKeys #-}
 
-delRecord :: PID -> WorkflowDB -> IO ()
+delRecord :: Key -> WorkflowDB -> IO ()
 delRecord pid (WorkflowDB db) =
     execute db (Query $ T.pack $ printf
         "DELETE FROM %s WHERE pid = ?" dbTableName) [pid]
diff --git a/src/Scientific/Workflow/Main.hs b/src/Scientific/Workflow/Main.hs
--- a/src/Scientific/Workflow/Main.hs
+++ b/src/Scientific/Workflow/Main.hs
@@ -41,7 +41,7 @@
 import           Data.Serialize                             (encode)
 import qualified Data.Text                                  as T
 import qualified Data.Text.Lazy.IO                          as T
-import           Data.Yaml                                  (FromJSON, decode)
+import           Data.Yaml                                  (FromJSON, decodeEither)
 
 #ifdef DRMAA_ENABLED
 import           DRMAA                                      (withSession)
@@ -218,10 +218,10 @@
         config <- case configuration opts of
             [] -> return def
             fls -> do
-                r <- decode . B.unlines <$> mapM B.readFile fls
+                r <- decodeEither . B.unlines <$> mapM B.readFile fls
                 case r of
-                    Nothing -> error "fail to parse configuration file"
-                    Just x  -> return x
+                    Left err -> error err
+                    Right x  -> return x
 
         result <- runReaderT (runExceptT $ runReaderT (wf ()) initState) config
         case result of
diff --git a/src/Scientific/Workflow/Main/Options.hs b/src/Scientific/Workflow/Main/Options.hs
--- a/src/Scientific/Workflow/Main/Options.hs
+++ b/src/Scientific/Workflow/Main/Options.hs
@@ -75,7 +75,7 @@
   where
     f x = case x of
         ('\\' : '0' : rest) -> '\0' : rest
-        x' -> x'
+        x'                  -> x'
 
 viewParser :: Parser CMD
 viewParser = View <$> switch (long "raw")
diff --git a/src/Scientific/Workflow/Visualize.hs b/src/Scientific/Workflow/Visualize.hs
--- a/src/Scientific/Workflow/Visualize.hs
+++ b/src/Scientific/Workflow/Visualize.hs
@@ -22,7 +22,7 @@
     fmtnode (_, (i, attr)) = [G.Label $ G.HtmlLabel label]
       where
         label = H.Table $ H.HTable (Just []) tableAttr $ header : H.HorizontalRule :
-            map toLine (wrap 45 $ attr^.note)
+            map toLine (wrap 45 $ if T.null (attr^.note) then "Empty" else attr^.note)
         header = H.Cells [H.LabelCell [] $ H.Text
             [ H.Format H.Bold $ [H.Font [H.PointSize 18] [H.Str $ TL.fromStrict i]]
             ]]