diff --git a/artifice/billing/csv_invoice.py b/artifice/billing/csv_invoice.py
index 6303e21..c1edca2 100644
--- a/artifice/billing/csv_invoice.py
+++ b/artifice/billing/csv_invoice.py
@@ -1,12 +1,12 @@
 import os
 from csv import writer
 from artifice import invoice
-from artifice import clerk_mixins
+# from artifice import clerk_mixins
 import yaml
 from decimal import *
 
 
-class Csv(clerk_mixins.ClerkRatesMixin, invoice.Invoice):
+class Csv(invoice.RatesFileMixin, invoice.Invoice):
 
     def __init__(self, tenant, start, end, config):
         self.config = config
diff --git a/artifice/database.py b/artifice/database.py
index 7c99374..e4c3557 100644
--- a/artifice/database.py
+++ b/artifice/database.py
@@ -1,7 +1,5 @@
 from sqlalchemy import func
-from .models.db_models import Tenant as tenant_model
-from .models.db_models import UsageEntry, Resource
-from .models import billing, Base
+from .models import billing, Base, Tenant, Resource, UsageEntry
 import collections
 
 import json
@@ -61,12 +59,12 @@ class Database(object):
         """Returns a list of tenants based on the usage entries
            in the given range.
            start, end: define the range to query
-           teants: is a iterable of tenants,
+           tenants: is a iterable of tenants,
                    if not given will default to whole tenant list."""
 
         if tenants is None:
-            tenants = self.session.query(tenant_model.tenant_id).\
-                filter(tenant_model.active)
+            tenants = self.session.query(Tenant.tenant_id).\
+                filter(Tenant.active)
         elif not isinstance(tenants, collections.Iterable):
             raise AttributeError("tenants is not an iterable")
 
@@ -103,8 +101,8 @@ class Database(object):
                 resource.usage_strategies[entry.service] = usage_strat
 
                 # build tenant:
-                name = self.session.query(tenant_model.name).\
-                    filter(tenant_model.tenant_id == entry.tenant_id)
+                name = self.session.query(Tenant.name).\
+                    filter(Tenant.tenant_id == entry.tenant_id)
                 tenant = billing.Tenant(name[0].name, entry.tenant_id)
                 # add resource to tenant:
                 tenant.resources[entry.resource_id] = resource
diff --git a/artifice/invoice.py b/artifice/invoice.py
index baccbff..8704bcc 100644
--- a/artifice/invoice.py
+++ b/artifice/invoice.py
@@ -118,7 +118,7 @@ class RatesFileMixin(object):
     # Adds a rates file loader, expecting various things from the
     # configuration
 
-    def rate(self, name):
+    def rate(self, name, region=None):
         try:
             self.__rates
         except AttributeError:
diff --git a/artifice/models/__init__.py b/artifice/models/__init__.py
index 1545f9e..0bd598d 100644
--- a/artifice/models/__init__.py
+++ b/artifice/models/__init__.py
@@ -1,8 +1,48 @@
 from sqlalchemy.ext.declarative import declarative_base
-from sqlalchemy import create_engine
 from sqlalchemy.orm import sessionmaker
+from sqlalchemy import Column, Text, DateTime, Boolean, DECIMAL
 
 Base = declarative_base()
 #
 
-Session = sessionmaker()
\ No newline at end of file
+Session = sessionmaker()
+
+
+class UsageEntry(Base):
+    """Simplified data store of usage information for a given service,
+       in a resource, in a tenant. Similar to ceilometer datastore,
+       but stores local transformed data."""
+    __tablename__ = 'usage'
+    service = Column(Text, primary_key=True)
+    volume = Column(DECIMAL)
+    resource_id = Column(Text, primary_key=True)
+    tenant_id = Column(Text, primary_key=True)
+    start = Column(DateTime)
+    end = Column(DateTime, primary_key=True)
+
+
+class Resource(Base):
+    """Database model for storing metadata associated with a resource."""
+    __tablename__ = 'resources'
+    resource_id = Column(Text, primary_key=True)
+    info = Column(Text)
+
+
+# this might not be a needed model?
+class SalesOrder(Base):
+    """Historic billing periods so that tenants cannot be rebuild accidentally."""
+    __tablename__ = 'sales_orders'
+    tenant_id = Column(Text, primary_key=True)
+    start = Column(DateTime)
+    end = Column(DateTime, primary_key=True)
+
+
+class Tenant(Base):
+    """Model for storage of metadata related to a tenant."""
+    __tablename__ = 'tenants'
+    # ID is a uuid
+    tenant_id = Column(Text, primary_key=True, nullable=False)
+    name = Column(Text)
+    info = Column(Text)
+    active = Column(Boolean, default=True)
+    # Some reference data to something else?
diff --git a/artifice/models/db_models.py b/artifice/models/db_models.py
deleted file mode 100644
index 1939312..0000000
--- a/artifice/models/db_models.py
+++ /dev/null
@@ -1,36 +0,0 @@
-from . import Base
-from sqlalchemy import Column, Text, DateTime, Boolean, DECIMAL
-
-
-class UsageEntry(Base):
-    __tablename__ = 'usage'
-    service = Column(Text, primary_key=True)
-    volume = Column(DECIMAL)
-    resource_id = Column(Text, primary_key=True)
-    tenant_id = Column(Text, primary_key=True)
-    start = Column(DateTime)
-    end = Column(DateTime, primary_key=True)
-
-
-class Resource(Base):
-    __tablename__ = 'resources'
-    resource_id = Column(Text, primary_key=True)
-    info = Column(Text)
-
-
-class SalesOrder(Base):
-    __tablename__ = 'sales_orders'
-    tenant_id = Column(Text, primary_key=True)
-    start = Column(DateTime)
-    end = Column(DateTime, primary_key=True)
-
-
-class Tenant(Base):
-
-    __tablename__ = 'tenants'
-    # ID is a uuid
-    tenant_id = Column(Text, primary_key=True, nullable=False)
-    name = Column(Text)
-    info = Column(Text)
-    active = Column(Boolean, default=True)
-    # Some reference data to something else?
diff --git a/examples/csv_rates.csv b/examples/csv_rates.csv
index cfd5356..027f2ce 100644
--- a/examples/csv_rates.csv
+++ b/examples/csv_rates.csv
@@ -1,8 +1,8 @@
-region | m1.nano  | duration       | 0.32
-region | m1.micro  | duration       | 0.42
-region | m1.tiny  | duration       | 0.62
-region | m1.small  | duration       | 0.82
-region | m1.medium  | duration       | 1.02
+region | m1_nano  | duration       | 0.32
+region | m1_micro  | duration       | 0.42
+region | m1_tiny  | duration       | 0.62
+region | m1_small  | duration       | 0.82
+region | m1_medium  | duration       | 1.02
 region | incoming_megabytes  | bytes          | 0.004
 region | outgoing_megabytes  | bytes          | 0.007
 region | storage_size    | bytes per hour | 0.000513
diff --git a/tests/test_DB_transform.py b/tests/test_DB_transform.py
index 3244eea..fc6904b 100644
--- a/tests/test_DB_transform.py
+++ b/tests/test_DB_transform.py
@@ -1,7 +1,7 @@
 from . import test_interface
 from decimal import Decimal
 from artifice import database
-from artifice.models.db_models import Tenant
+from artifice.models import Tenant
 from sqlalchemy.ext.declarative import declarative_base
 
 Base = declarative_base()
diff --git a/tests/test_csv_invoice.py b/tests/test_csv_invoice.py
index 8344aa0..6ac809e 100644
--- a/tests/test_csv_invoice.py
+++ b/tests/test_csv_invoice.py
@@ -1,6 +1,6 @@
 from . import test_interface
 from artifice import database
-from artifice.models.db_models import Tenant
+from artifice.models import Tenant
 from sqlalchemy.ext.declarative import declarative_base
 
 from artifice.billing import csv_invoice
@@ -10,7 +10,7 @@ Base = declarative_base()
 
 config = {
     "output_file": '%(tenant)s-%(start)s-%(end)s.csv',
-    "output_path": "./invoices",
+    "output_path": "./tests/invoices",
     "rates": {"file":
               "/home/adriant/Projects/openstack-artifice/examples/csv_rates.csv"}
 }
diff --git a/tests/test_interface.py b/tests/test_interface.py
index 7d4b5fb..3561d91 100644
--- a/tests/test_interface.py
+++ b/tests/test_interface.py
@@ -4,8 +4,8 @@ from artifice.interface import Artifice
 import mock
 import random
 import json
-from artifice.models.db_models import Tenant as tenant_model
-from artifice.models.db_models import UsageEntry, Resource
+from artifice.models import Tenant as tenant_model
+from artifice.models import UsageEntry, Resource
 # import copy
 
 from sqlalchemy import create_engine