diff -r 4bb38d03e430 -r 40e125004a0b src/hdalab/models/dataviz.py
--- a/src/hdalab/models/dataviz.py	Thu Apr 02 22:52:54 2015 +0200
+++ b/src/hdalab/models/dataviz.py	Fri Apr 03 02:22:15 2015 +0200
@@ -12,7 +12,7 @@
 
 class TagYears(models.Model):
     
-    tag = models.ForeignKey(Tag, related_name="years", blank=False, null=False, db_index=True, unique=True)
+    tag = models.OneToOneField(Tag, related_name="years", blank=False, null=False, db_index=True)
     start_year = models.IntegerField(blank=False, null=False, db_index=True)
     end_year = models.IntegerField(blank=False, null=False, db_index=True)