diff --git a/iTunesParser.py b/iTunesParser.py
index 85cc7e1..b5e0a98 100644
--- a/iTunesParser.py
+++ b/iTunesParser.py
@@ -45,6 +45,7 @@ import os
 import plistlib
 import sys
 import argparse
+import hashlib
 
 
 class SetEncoder(json.JSONEncoder):
@@ -135,8 +136,9 @@ class ITunesParser:
         akey = track['Artist']
         # Add artist
         if akey not in self._artists:
+            a_id = self.calc_id(akey)
             self._artists[akey] = {
-                'id': len(self._artists), # TODO Calc an uniq ID (permit to replace data)
+                'Persistent ID': a_id,
                 'Name': akey,
                 'Track Count': 0,
                 'Play Count': 0,
@@ -149,7 +151,7 @@ class ITunesParser:
         # TODO If no Rating, don't take 0
         play_count = track['Play Count'] if 'Play Count' in track else 0
 
-        rating = self._calc_rating(rating, self._artists[akey]['Rating'], self._artists[akey]['Track Count'])
+        rating = self.calc_rating(rating, self._artists[akey]['Rating'], self._artists[akey]['Track Count'])
 
         self._artists[akey]['Track Count'] += 1
         self._artists[akey]['Rating'] = rating
@@ -173,14 +175,15 @@ class ITunesParser:
 
         akey = track['Album']
         if akey not in self._albums:
+            a_id = self.calc_id(akey)
             self._albums[akey] = {
-                'id': len(self._albums),
+                'Persistent ID': a_id,
                 'Name': akey,
                 'Track Count': 0,
                 'Play Count': 0,
                 'Rating': 0,
                 'Genre': set(),
-                'artist': set()
+                'Artist': set()
             }
 
         # Compute information
@@ -189,7 +192,7 @@ class ITunesParser:
         # TODO If no Rating, don't take 0
         play_count = track['Play Count'] if 'Play Count' in track else 0
 
-        rating = self._calc_rating(rating, self._albums[akey]['Rating'], self._albums[akey]['Track Count'])
+        rating = self.calc_rating(rating, self._albums[akey]['Rating'], self._albums[akey]['Track Count'])
 
         self._albums[akey]['Track Count'] += 1
         self._albums[akey]['Rating'] = rating
@@ -205,7 +208,7 @@ class ITunesParser:
         ## Add different artists
         if 'Artist' not in track:
             return
-        self._albums[akey]['artist'].add(track['Artist'])
+        self._albums[akey]['Artist'].add(track['Artist'])
         return
 
     def _write_artists(self):
@@ -215,8 +218,9 @@ class ITunesParser:
 
         file_artist = io.open('es-artist-data.json', 'wb')
         for artist in self._artists:
+            persistent_id = self._artists[artist]['Persistent ID']
             json_track_index = {
-                "index": {"_index": "itunessongs", "_type": "artist"}
+                "index": {"_index": "itunessongs", "_type": "artist", "_id": persistent_id}
             }
             file_artist.write(bytes(json.dumps(json_track_index, indent=None, cls=SetEncoder), 'UTF-8'))
             file_artist.write(bytes("\n", 'UTF-8'))
@@ -231,8 +235,9 @@ class ITunesParser:
 
         file_albums = io.open('es-albums-data.json', 'wb')
         for album in self._albums:
+            persistent_id = self._albums[album]['Persistent ID']
             json_track_index = {
-                "index": {"_index": "itunessongs", "_type": "album"}
+                "index": {"_index": "itunessongs", "_type": "album", "_id": persistent_id}
             }
             file_albums.write(bytes(json.dumps(json_track_index, indent=None, cls=SetEncoder), 'UTF-8'))
             file_albums.write(bytes("\n", 'UTF-8'))
@@ -240,9 +245,22 @@ class ITunesParser:
             file_albums.write(bytes("\n", 'UTF-8'))
         file_albums.close()
 
-    def _calc_rating(self, added_value, current_rating, count):
+    @classmethod
+    def calc_rating(cls, added_value, current_rating, count):
+        """
+            Calculate average rating from a current rating, a rating value to add and the number of elements
+        """
         return (current_rating * count + added_value) // (count + 1)
 
+    @classmethod
+    def calc_id(cls, key):
+        """
+            Calculate a MD5 sum from a key as ID
+        """
+        md5 = hashlib.md5()
+        md5.update(key.encode('UTF-8'))
+        return md5.hexdigest()
+
 #### main block ####
 
 # Default input & output files