Support multiple database through a ZConfig file. You can still do the

file_storage shortcut if you don't want a separate file and a Data.fs is
enough for you.

zope/paste/factory.py

@@ -1,12 +1,36 @@
+import os.path
+import ZConfig
+import zope.event
 import zope.app.appsetup
+from zope.app.appsetup.appsetup import multi_database
 from zope.app.wsgi import WSGIPublisherApplication
 
-def zope_app_factory(global_conf, site_definition, file_storage,
-                     devmode='no'):
+def zope_app_factory(global_conf, site_definition, file_storage=None,
+                     db_definition=None, devmode='no'):
+    # load ZCML (usually site.zcml)
     features = ()
     if devmode.lower() in ('yes', 'true', 'on'):
         features += ('devmode',)
     zope.app.appsetup.config(site_definition, features)
 
-    db = zope.app.appsetup.database(file_storage)
+    if file_storage is None and db_definition is None:
+        raise TypeError("You must either provide a 'file_storage' or a "
+                        "'db_definition' setting.")
+
+    if file_storage is not None and db_definition is not None:
+        raise TypeError("You may only provide a 'file_storage' or a "
+                        "'db_definition' setting, not both.")
+
+    # open database
+    if file_storage is not None:
+        db = zope.app.appsetup.database(file_storage)
+    else:
+        schema_xml = os.path.join(os.path.dirname(__file__), 'schema.xml')
+        schema = ZConfig.loadSchema(schema_xml)
+        cfgroot, cfghandlers = ZConfig.loadConfig(schema, db_definition)
+
+        result, databases = multi_database(cfgroot.databases)
+        db = result[0]
+        zope.event.notify(zope.app.appsetup.DatabaseOpened(db))
+
     return WSGIPublisherApplication(db)

zope/paste/schema.xml

@@ -0,0 +1,5 @@
+<schema>
+  <import package="ZODB" />
+  <multisection type="ZODB.database" name="*" required="yes"
+                attribute="databases" />
+</schema>