diff --git a/scopes/organize/__init__.py b/scopes/organize/__init__.py
new file mode 100644
index 0000000..829e828
--- /dev/null
+++ b/scopes/organize/__init__.py
@@ -0,0 +1 @@
+"""package scopes.organize"""
diff --git a/scopes/storage/common.py b/scopes/storage/common.py
index 89f6673..6d04ec1 100644
--- a/scopes/storage/common.py
+++ b/scopes/storage/common.py
@@ -71,8 +71,10 @@ class Storage(object):
 registry = {}
 
 def registerContainerClass(cls):
-    # TODO: error on duplicate key
-    registry[cls.itemFactory.prefix] = cls
+    prefix = cls.itemFactory.prefix
+    if prefix in registry:
+        raise ValueError("prefix '%s' already registered!" % prefix)
+    registry[prefix] = cls
     cls.headCols = cols = tuple(f.lower() for f in cls.itemFactory.headFields)
     if cls.indexes is None:
         cls.indexes = [cols[i:] for i in range(len(cols))]
diff --git a/scopes/storage/concept.py b/scopes/storage/concept.py
new file mode 100644
index 0000000..967f3a4
--- /dev/null
+++ b/scopes/storage/concept.py
@@ -0,0 +1,12 @@
+# scopes.storage.concept
+
+"""Abstract base classes for concept map application classes."""
+
+from scopes.storage.common import registerContainerClass
+from scopes.storage.tracking import Container, Track
+
+
+class Concept(Track):
+
+    headFields = ['parent', 'name']
+ 
diff --git a/scopes/storage/folder.py b/scopes/storage/folder.py
index 6a0eb88..c5e80d5 100644
--- a/scopes/storage/folder.py
+++ b/scopes/storage/folder.py
@@ -10,23 +10,23 @@ class Folder(Track):
     prefix = 'fldr'
 
     def keys(self):
-        for f in self.container.query(parent=self.uid):
+        for f in self.container.query(parent=self.name):
             yield f.name
 
     def get(self, key, default=None):
-        value = self.container.queryLast(parent=self.uid, name=key)
+        value = self.container.queryLast(parent=self.name, name=key)
         if value is None:
             return default
         return value
 
     def __getitem__(self, key):
-        value = self.container.queryLast(parent=self.uid, name=key)
+        value = self.container.queryLast(parent=self.name, name=key)
         if value is None:
             raise KeyError(key)
         return value
 
     def __setitem__(self, key, value):
-        value.set('parent', self.uid)
+        value.set('parent', self.name)
         value.set('name', key)
         self.container.save(value)
 
diff --git a/scopes/storage/relation.py b/scopes/storage/relation.py
new file mode 100644
index 0000000..100528e
--- /dev/null
+++ b/scopes/storage/relation.py
@@ -0,0 +1,3 @@
+# scopes.storage.relation
+
+"""An SQL-based relationship engine using RDF-like triples."""
diff --git a/tests/test_storage.py b/tests/test_storage.py
index ed49eec..ab234ad 100644
--- a/tests/test_storage.py
+++ b/tests/test_storage.py
@@ -80,7 +80,7 @@ class Test(unittest.TestCase):
         top['child1'] = folder.Folder(data=dict(title='First Child'))
         self.assertEqual(list(top.keys()), ['child1'])
         ch1 = top['child1']
-        self.assertEqual(ch1.parent, top.uid)
+        self.assertEqual(ch1.parent, top.name)
         assert list(top.keys()) == ['child1']
 
 def suite():