diff --git a/commerce/interfaces.py b/commerce/interfaces.py
index bb22c12..c7631ef 100644
--- a/commerce/interfaces.py
+++ b/commerce/interfaces.py
@@ -32,9 +32,117 @@ from cybertools.util.jeep import Jeep, Term
 _ = MessageFactory('cybertools.commerce')
 
 
+# shops
+
+class IShop(Interface):
+    """ A shop with products and customers.
+    """
+
+    name = schema.TextLine(
+            title=_(u'Shop name'),
+            description=_(u'An internal name uniquely identifying the shop.'),
+            default=u'',
+            required=True)
+    title = schema.TextLine(
+            title=_(u'Title'),
+            description=_(u'Short title of the shop.'),
+            default=u'',
+            required=True)
+    description = schema.Text(
+            title=_(u'Description'),
+            description=_(u'A medium-length description.'),
+            default=u'',
+            missing_value=u'',
+            required=False)
+
+    products = Attribute(u'The products available in this shop.')
+    categories = Attribute(u'The product categories provided by this shop.')
+    customers = Attribute(u'The customers registered for this shop.')
+
+
 # products
 
 class IProduct(Interface):
     """ A certain class of similar objects that may be put in a shopping cart.
     """
 
+    productId = schema.TextLine(
+            title=_(u'Product Identifier'),
+            description=_(u'A name or number uniquely identifiying the '
+                    u'product within a shop.'),
+            default=u'',
+            required=True)
+    title = schema.TextLine(
+            title=_(u'Title'),
+            description=_(u'Short title of the product.'),
+            default=u'',
+            required=True)
+    description = schema.Text(
+            title=_(u'Description'),
+            description=_(u'A medium-length description of the product.'),
+            default=u'',
+            missing_value=u'',
+            required=False)
+
+    categories = Attribute(u'The product categories this product belongs to.')
+    shops = Attribute(u'The shops providing this product.')
+
+
+class ICategory(Interface):
+    """ A product category.
+    """
+
+    title = schema.TextLine(
+            title=_(u'Title'),
+            description=_(u'Short title of the category.'),
+            default=u'',
+            required=True)
+    description = schema.Text(
+            title=_(u'Description'),
+            description=_(u'A medium-length description of the category.'),
+            default=u'',
+            missing_value=u'',
+            required=False)
+
+    products = Attribute(u'The products belonging to this category.')
+    subcategories = Attribute(u'The sub-categories belonging to this category.')
+    shops = Attribute(u'The shops providing this category.')
+
+
+# customers
+
+class ICustomer(Interface):
+    """ A role of - for example - a person or institution (the ``client``)
+        representing a customer of one or more shops.
+    """
+
+    customerId = schema.TextLine(
+            title=_(u'Customer Identifier'),
+            description=_(u'A name or number uniquely identifiying the customer.'),
+            default=u'',
+            required=True)
+
+    client = Attribute(u'The (real) client object of the customer role.')
+    shops = Attribute(u'The shops the client object is a customer of.')
+
+
+# orders
+
+class IOrder(Interface):
+    """
+    """
+
+    orderId = Attribute(u'Order Identifier')
+    shop = Attribute(u'The shop this order is for.')
+    customer = Attribute(u'The customer issuing this order.')
+
+
+class IOrderItem(Interface):
+    """
+    """
+
+    order = Attribute(u'Order this order item belongs to.')
+    product = Attribute(u'The product represented by this order item.')
+    amount = Attribute(u'The number of product items ordered.')
+    unitPrice = Attribute(u'The basic unit price for one of the product '
+                    u'items ordered.')