diff --git a/core/models/survex.py b/core/models/survex.py
index 0e336ab..469628a 100644
--- a/core/models/survex.py
+++ b/core/models/survex.py
@@ -130,6 +130,7 @@ class SurvexBlockLookUpManager(models.Manager):
 class SurvexBlock(models.Model):
     """One begin..end block within a survex file. The basic element of a survey trip.
     Multiple anonymous survex blocks are possible within the same surfex file
+    Blocks can span several *included survexfile though.
     """
 
     objects = SurvexBlockLookUpManager() # overwrites SurvexBlock.objects and enables lookup()
@@ -139,8 +140,9 @@ class SurvexBlock(models.Model):
 
     date = models.DateField(blank=True, null=True)
     expedition = models.ForeignKey("Expedition", blank=True, null=True, on_delete=models.SET_NULL)
-
-    survexfile = models.ForeignKey("SurvexFile", blank=True, null=True, on_delete=models.SET_NULL)
+    # if the survexfile object is deleted, then all teh suvex-blocks in it should be too,
+    # though a block can span more than one file...
+    survexfile = models.ForeignKey("SurvexFile", blank=True, null=True, on_delete=models.CASCADE)
     survexpath = models.CharField(max_length=200)  # the path for the survex stations
 
     scanswallet = models.ForeignKey(
@@ -209,7 +211,8 @@ class SingleScan(models.Model):
 
 
 class DrawingFile(models.Model):
-    """A file holding a Therion (several types) or a Tunnel drawing"""
+    """A file holding a Therion (several types) or a Tunnel drawing
+    Most of the implied capabilities are not implemented yet"""
 
     dwgpath = models.CharField(max_length=200)
     dwgname = models.CharField(max_length=200)