diff --git a/.travis.yml b/.travis.yml
index a6f4d3c..eff8101 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -8,7 +8,7 @@ matrix:
       dist: xenial
       sudo: true
 env:
-  - TRAVIS=yes
+  - TRAVIS=yes AWS_ACCESS_KEY_ID=test AWS_SECRET_ACCESS_KEY=test
 before_install:
   - pip install -U pip && pip --version
   - wget https://repo.anaconda.com/miniconda/Miniconda3-4.6.14-Linux-x86_64.sh -O miniconda.sh
diff --git a/CHANGES.txt b/CHANGES.txt
index a626264..534fb56 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1,3 +1,20 @@
+v1.2.3 - 2020-05-07
+===================
+
+- Updated requirements in order to use newer versions of dependencies
+  (also fixing potential security vulnerabilities in dependencies)
+
+- Added support for handling model attachments
+
+- Exclamation mark `!` can now be used instead of `__factory__` in
+  configuration files
+
+v1.2.2.1 - 2019-09-30
+=====================
+
+- Added AWS S3 persister
+
+
 v1.2.2 - 2019-08-15
 ===================
 
diff --git a/VERSION b/VERSION
index 23aa839..0495c4a 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-1.2.2
+1.2.3
diff --git a/docs/user/R.rst b/docs/user/R.rst
index 4c720e1..00ccf60 100644
--- a/docs/user/R.rst
+++ b/docs/user/R.rst
@@ -42,7 +42,7 @@ above:
 .. code-block:: python
 
   'dataset_loader_train': {
-      '__factory__': 'palladium.R.DatasetLoader',
+      '!': 'palladium.R.DatasetLoader',
       'scriptname': 'iris.R',
       'funcname': 'dataset',
       },
@@ -54,7 +54,7 @@ R classification models are configured very similarly, using
 .. code-block:: python
 
   'model': {
-      '__factory__': 'palladium.R.ClassificationModel',
+      '!': 'palladium.R.ClassificationModel',
       'scriptname': 'iris.R',
       'funcname': 'train.randomForest',
       'encode_labels': True,
@@ -99,7 +99,7 @@ Here's how this would look like:
 .. code-block:: python
 
   'model': {
-      '__factory__': 'palladium.R.RegressionModel',
+      '!': 'palladium.R.RegressionModel',
       'scriptname': 'tooth.R',
       'funcname': 'train.randomForest',
       },
@@ -110,7 +110,7 @@ classification above:
 .. code-block:: python
 
     'dataset_loader_train': {
-        '__factory__': 'palladium.R.DatasetLoader',
+        '!': 'palladium.R.DatasetLoader',
         'scriptname': 'tooth.R',
         'funcname': 'dataset',
     },
@@ -129,13 +129,13 @@ including :class:`~palladium.R.Rpy2Transform` in a
 .. code-block:: python
 
     'model': {
-        '__factory__': 'sklearn.pipeline.Pipeline',
+        '!': 'sklearn.pipeline.Pipeline',
         'steps': [
             ['rpy2', {
-                '__factory__': 'palladium.R.Rpy2Transform',
+                '!': 'palladium.R.Rpy2Transform',
             }],
             ['regressor', {
-                '__factory__': 'palladium.R.RegressionModel',
+                '!': 'palladium.R.RegressionModel',
                 'scriptname': 'tooth.R',
                 'funcname': 'train.randomForest',
             }],
diff --git a/docs/user/configuration.rst b/docs/user/configuration.rst
index 5004919..defdfd3 100644
--- a/docs/user/configuration.rst
+++ b/docs/user/configuration.rst
@@ -31,7 +31,7 @@ you to pass in things like database credentials from the environment:
 .. code-block:: python
 
     'dataset_loader_train': {
-        '__factory__': 'palladium.dataset.SQL',
+        '!': 'palladium.dataset.SQL',
         'url': 'mysql://{}:{}@localhost/test?encoding=utf8'.format(
             environ['DB_USER'], environ['DB_PASS'],
             ),
@@ -46,7 +46,7 @@ folder as the configuration:
 .. code-block:: python
 
     'dataset_loader_train': {
-        '__factory__': 'palladium.dataset.CSV',
+        '!': 'palladium.dataset.CSV',
         'path': '{}/data.csv'.format(here),
         }
 
@@ -80,7 +80,7 @@ file:
 .. code-block:: python
 
     'dataset_loader_train': {
-        '__factory__': 'palladium.dataset.CSV',
+        '!': 'palladium.dataset.CSV',
         'path': '{}/train.csv'.format(here),
         'many': '...',
         'more': {'...'},
@@ -88,7 +88,7 @@ file:
         }
 
     'dataset_loader_test': {
-        '__factory__': 'palladium.dataset.CSV',
+        '!': 'palladium.dataset.CSV',
         'path': '{}/test.csv'.format(here),
         'many': '...',
         'more': {'...'},
@@ -100,7 +100,7 @@ With ``__copy__``, you can reduce this down to:
 .. code-block:: python
 
     'dataset_loader_train': {
-        '__factory__': 'palladium.dataset.CSV',
+        '!': 'palladium.dataset.CSV',
         'path': '{}/train.csv'.format(here),
         'many': '...',
         'more': {'...'},
diff --git a/docs/user/deployment.rst b/docs/user/deployment.rst
index ca971c4..2b45871 100644
--- a/docs/user/deployment.rst
+++ b/docs/user/deployment.rst
@@ -421,7 +421,7 @@ startup:
 .. code-block:: python
 
   'oauth_init_app': {
-      '__factory__': 'myoauth.oauth.init_app',
+      '!': 'myoauth.oauth.init_app',
       'app': 'palladium.server.app',
       },
 
diff --git a/docs/user/faq.rst b/docs/user/faq.rst
index 89655b3..c5ae981 100644
--- a/docs/user/faq.rst
+++ b/docs/user/faq.rst
@@ -156,7 +156,7 @@ passed at runtime.
             'C': [0.1, 0.3, 1.0],
             },
         'cv': {
-            '__factory__': 'palladium.util.Partial',
+            '!': 'palladium.util.Partial',
             'func': 'sklearn.cross_validation.StratifiedKFold',
             'random_state': 0,
             },
@@ -177,16 +177,16 @@ classifier:
 .. code-block:: python
 
     'grid_search': {
-        '__factory__': 'skopt.BayesSearchCV',
+        '!': 'skopt.BayesSearchCV',
         'estimator': {'__copy__': 'model'},
         'n_iter': 16,
         'search_spaces': {
             'C': {
-                '__factory__': 'skopt.space.Real',
+                '!': 'skopt.space.Real',
                 'low': 1e-6, 'high': 1e+1, 'prior': 'log-uniform',
             },
             'degree': {
-                '__factory__': 'skopt.space.Integer',
+                '!': 'skopt.space.Integer',
                 'low': 1, 'high': 20,
             },
         },
@@ -208,35 +208,34 @@ grid search:
 
 .. code-block:: python
 
+{
     'grid_search': {
-        '__factory__': 'palladium.fit.with_parallel_backend',
+        '!': 'palladium.fit.with_parallel_backend',
         'estimator': {
-            '__factory__': 'sklearn.model_selection.GridSearchCV',
+            '!': 'sklearn.model_selection.GridSearchCV',
             'estimator': {'__copy__': 'model'},
-            'param_grid': {
-                'C': [0.1, 0.3, 1.0],
-            },
-            'n_jobs': -1,
+            'param_grid': {'__copy__': 'grid_search.param_grid'},
+            'scoring': {'__copy__': 'scoring'},
         },
-        'backend': 'dask.distributed',
-        'scheduler_host': '127.0.0.1:8786',
+        'backend': 'dask',
     },
 
-    '_init_distributed': {
-        '__factory__': 'palladium.util.resolve_dotted_name',
-        'dotted_name': 'distributed.joblib.joblib',
+    '_init_client': {
+        '!': 'dask.distributed.Client',
+        'address': '127.0.0.1:8786',
     },
+}
 
-To start up the Dask scheduler and workers you can follow the
-dask.distributed documentation.  Here's an example that runs three
-workers locally:
+For details on how to set up Dask workers and a scheduler, please
+consult the `Dask docs <https://docs.dask.org>`_.  But here's how you
+would start up a scheduler and three workers locally:
 
 .. code-block:: bash
 
     $ dask-scheduler
     Scheduler started at 127.0.0.1:8786
 
-    $ dask-worker 127.0.0.1:8786
+    $ dask-worker 127.0.0.1:8786  # start each in a new terminal
     $ dask-worker 127.0.0.1:8786
     $ dask-worker 127.0.0.1:8786    
 
diff --git a/docs/user/julia.rst b/docs/user/julia.rst
index 5154b14..b2af4f7 100644
--- a/docs/user/julia.rst
+++ b/docs/user/julia.rst
@@ -44,7 +44,7 @@ configuration in that example defines the model to be of type
 .. code-block:: python
 
   'model': {
-      '__factory__': 'palladium.julia.ClassificationModel',
+      '!': 'palladium.julia.ClassificationModel',
       'fit_func': 'SVM.svm',
       'predict_func': 'SVM.predict',
       }
diff --git a/docs/user/tutorial.rst b/docs/user/tutorial.rst
index 3d06de4..62b8890 100644
--- a/docs/user/tutorial.rst
+++ b/docs/user/tutorial.rst
@@ -149,7 +149,7 @@ defines the type of dataset loader we want to use.  That is
 .. code-block:: python
 
     'dataset_loader_train': {
-        '__factory__': 'palladium.dataset.CSV',
+        '!': 'palladium.dataset.CSV',
 
 The rest of what is inside the ``dataset_loader_train`` are the
 keyword arguments that are used to initialize the
@@ -159,7 +159,7 @@ keyword arguments that are used to initialize the
 .. code-block:: python
 
     'dataset_loader_train': {
-        '__factory__': 'palladium.dataset.CSV',
+        '!': 'palladium.dataset.CSV',
         'path': 'iris.data',
         'names': [
             'sepal length',
@@ -232,7 +232,7 @@ scikit-learn:
 .. code-block:: python
 
     'model': {
-        '__factory__': 'sklearn.linear_model.LogisticRegression',
+        '!': 'sklearn.linear_model.LogisticRegression',
         'C': 0.3,
         },
 
@@ -367,10 +367,10 @@ part of the configuration:
 .. code-block:: python
 
     'model_persister': {
-        '__factory__': 'palladium.persistence.CachedUpdatePersister',
+        '!': 'palladium.persistence.CachedUpdatePersister',
         'update_cache_rrule': {'freq': 'HOURLY'},
         'impl': {
-            '__factory__': 'palladium.persistence.Database',
+            '!': 'palladium.persistence.Database',
             'url': 'sqlite:///iris-model.db',
             },
         },
@@ -407,9 +407,9 @@ model's version:
 .. code-block:: python
 
     'model_persister': {
-        '__factory__': 'palladium.persistence.CachedUpdatePersister',
+        '!': 'palladium.persistence.CachedUpdatePersister',
         'impl': {
-            '__factory__': 'palladium.persistence.File',
+            '!': 'palladium.persistence.File',
             'path': 'model-{version}.pickle',
             },
         },
@@ -420,9 +420,9 @@ models, you can use the RestPersister:
 .. code-block:: python
 
     'model_persister': {
-        '__factory__': 'palladium.persistence.CachedUpdatePersister',
+        '!': 'palladium.persistence.CachedUpdatePersister',
         'impl': {
-            '__factory__': 'palladium.persistence.Rest',
+            '!': 'palladium.persistence.Rest',
             'url': 'http://localhost:8081/artifactory/modelz/{version}',
             'auth': ('username', 'passw0rd'),
             },
@@ -440,7 +440,7 @@ endpoint.  Let us take a look at how it is configured:
 .. code-block:: python
 
     'predict_service': {
-        '__factory__': 'palladium.server.PredictService',
+        '!': 'palladium.server.PredictService',
         'mapping': [
             ('sepal length', 'float'),
             ('sepal width', 'float'),
@@ -450,7 +450,7 @@ endpoint.  Let us take a look at how it is configured:
         }
 
 Again, the specific implementation of the ``predict_service`` that we
-use is specified through the ``__factory__`` setting.
+use is specified through the ``!`` setting.
 
 The ``mapping`` defines which request parameters are to be expected.
 In this example, we expect a ``float`` number for each of ``sepal
@@ -522,7 +522,7 @@ different entry points:
 .. code-block:: python
 
     'predict_service1': {
-        '__factory__': 'mypackage.server.PredictService',
+        '!': 'mypackage.server.PredictService',
         'mapping': [
             ('sepal length', 'float'),
             ('sepal width', 'float'),
@@ -533,7 +533,7 @@ different entry points:
 	'decorator_list_name': 'predict_decorators',
         }
     'predict_service2': {
-        '__factory__': 'mypackage.server.PredictServiceID',
+        '!': 'mypackage.server.PredictServiceID',
         'mapping': [
             ('id', 'int'),
             ],
@@ -590,7 +590,7 @@ entry in ``config.py`` to look like this:
 .. code-block:: python
 
     'model': {
-        '__factory__': 'iris.model',
+        '!': 'iris.model',
         'clf__C': 0.3,
         },
 
@@ -609,7 +609,7 @@ configuration file, e.g.:
 .. code-block:: python
 
     'model': {
-        '__factory__': 'sklearn.pipeline.Pipeline',
-        'steps': [['clf', {'__factory__': 'sklearn.linear_model.LinearRegression'}],
+        '!': 'sklearn.pipeline.Pipeline',
+        'steps': [['clf', {'!': 'sklearn.linear_model.LinearRegression'}],
         ],
     },
diff --git a/docs/user/web-service.rst b/docs/user/web-service.rst
index 647faba..b1caa5b 100644
--- a/docs/user/web-service.rst
+++ b/docs/user/web-service.rst
@@ -31,7 +31,7 @@ configuration from the :ref:`tutorial`:
 .. code-block:: python
 
     'predict_service': {
-        '__factory__': 'palladium.server.PredictService',
+        '!': 'palladium.server.PredictService',
         'mapping': [
             ('sepal length', 'float'),
             ('sepal width', 'float'),
@@ -106,7 +106,7 @@ there's a list of predictions that's returned:
 
 Should a different output format be desired than the one implemented
 by :class:`~palladium.interfaces.PredictService`, it is possible to use a
-different class altogether by setting an appropriate ``__factory__``
+different class altogether by setting an appropriate ``!``
 (though that class will likely derive from
 :class:`~palladium.interfaces.PredictService` for reasons of convenience).
 
@@ -271,13 +271,13 @@ endpoints is this:
 
     'flask_add_url_rules': [
         {
-            '__factory__': 'palladium.server.add_url_rule',
+            '!': 'palladium.server.add_url_rule',
             'rule': '/fit',
             'view_func': 'palladium.server.fit',
             'methods': ['POST'],
         },
         {
-            '__factory__': 'palladium.server.add_url_rule',
+            '!': 'palladium.server.add_url_rule',
             'rule': '/update-model-cache',
             'view_func': 'palladium.server.update_model_cache',
             'methods': ['POST'],
diff --git a/examples/R/config-iris-dataset-from-python.py b/examples/R/config-iris-dataset-from-python.py
index f4271a4..7f31a6c 100644
--- a/examples/R/config-iris-dataset-from-python.py
+++ b/examples/R/config-iris-dataset-from-python.py
@@ -4,7 +4,7 @@
 
 {
     'dataset_loader_train': {
-        '__factory__': 'palladium.dataset.CSV',
+        '!': 'palladium.dataset.CSV',
         'path': 'iris.data',
         'names': [
             'sepal length',
diff --git a/examples/R/config-iris.py b/examples/R/config-iris.py
index 40c4b06..c1338b2 100644
--- a/examples/R/config-iris.py
+++ b/examples/R/config-iris.py
@@ -5,34 +5,34 @@
     },
 
     'dataset_loader_train': {
-        '__factory__': 'palladium.R.DatasetLoader',
+        '!': 'palladium.R.DatasetLoader',
         'scriptname': 'iris.R',
         'funcname': 'dataset',
     },
 
     'dataset_loader_test': {
-        '__factory__': 'palladium.R.DatasetLoader',
+        '!': 'palladium.R.DatasetLoader',
         'scriptname': 'iris.R',
         'funcname': 'dataset',
     },
 
     'model': {
-        '__factory__': 'palladium.R.ClassificationModel',
+        '!': 'palladium.R.ClassificationModel',
         'scriptname': 'iris.R',
         'funcname': 'train.randomForest',
         'encode_labels': True,
     },
 
     'model_persister': {
-        '__factory__': 'palladium.persistence.CachedUpdatePersister',
+        '!': 'palladium.persistence.CachedUpdatePersister',
         'impl': {
-            '__factory__': 'palladium.persistence.Database',
+            '!': 'palladium.persistence.Database',
             'url': 'sqlite:///iris-model.db',
         },
     },
 
     'predict_service': {
-        '__factory__': 'palladium.server.PredictService',
+        '!': 'palladium.server.PredictService',
         'mapping': [
             ('sepal length', 'float'),
             ('sepal width', 'float'),
diff --git a/examples/R/config-tooth.py b/examples/R/config-tooth.py
index c403e6a..b2dc98e 100644
--- a/examples/R/config-tooth.py
+++ b/examples/R/config-tooth.py
@@ -5,25 +5,25 @@
     },
 
     'dataset_loader_train': {
-        '__factory__': 'palladium.R.DatasetLoader',
+        '!': 'palladium.R.DatasetLoader',
         'scriptname': 'tooth.R',
         'funcname': 'dataset',
     },
 
     'dataset_loader_test': {
-        '__factory__': 'palladium.R.DatasetLoader',
+        '!': 'palladium.R.DatasetLoader',
         'scriptname': 'tooth.R',
         'funcname': 'dataset',
     },
 
     'model': {
-        '__factory__': 'sklearn.pipeline.Pipeline',
+        '!': 'sklearn.pipeline.Pipeline',
         'steps': [
             ['rpy2', {
-                '__factory__': 'palladium.R.Rpy2Transform',
+                '!': 'palladium.R.Rpy2Transform',
             }],
             ['regressor', {
-                '__factory__': 'palladium.R.RegressionModel',
+                '!': 'palladium.R.RegressionModel',
                 'scriptname': 'tooth.R',
                 'funcname': 'train.randomForest',
             }],
@@ -31,15 +31,15 @@
     },
 
     'model_persister': {
-        '__factory__': 'palladium.persistence.CachedUpdatePersister',
+        '!': 'palladium.persistence.CachedUpdatePersister',
         'impl': {
-            '__factory__': 'palladium.persistence.Database',
+            '!': 'palladium.persistence.Database',
             'url': 'sqlite:///tooth-model.db',
         },
     },
 
     'predict_service': {
-        '__factory__': 'palladium.server.PredictService',
+        '!': 'palladium.server.PredictService',
         'mapping': [
             ('supp', 'str'),
             ('dose', 'float'),
diff --git a/examples/iris/config.py b/examples/iris/config.py
index e58ab22..16accb2 100644
--- a/examples/iris/config.py
+++ b/examples/iris/config.py
@@ -5,7 +5,7 @@
     },
 
     'dataset_loader_train': {
-        '__factory__': 'palladium.dataset.CSV',
+        '!': 'palladium.dataset.CSV',
         'path': 'iris.data',
         'names': [
             'sepal length',
@@ -19,7 +19,7 @@
     },
 
     'dataset_loader_test': {
-        '__factory__': 'palladium.dataset.CSV',
+        '!': 'palladium.dataset.CSV',
         'path': 'iris.data',
         'names': [
             'sepal length',
@@ -33,7 +33,7 @@
     },
 
     'model': {
-        '__factory__': 'sklearn.linear_model.LogisticRegression',
+        '!': 'sklearn.linear_model.LogisticRegression',
         'C': 0.3,
         'solver': 'lbfgs',
         'multi_class': 'auto',
@@ -49,16 +49,16 @@
     },
 
     'model_persister': {
-        '__factory__': 'palladium.persistence.CachedUpdatePersister',
+        '!': 'palladium.persistence.CachedUpdatePersister',
         'update_cache_rrule': {'freq': 'HOURLY'},
         'impl': {
-            '__factory__': 'palladium.persistence.Database',
+            '!': 'palladium.persistence.Database',
             'url': 'sqlite:///iris-model.db',
         },
     },
 
     'predict_service': {
-        '__factory__': 'palladium.server.PredictService',
+        '!': 'palladium.server.PredictService',
         'mapping': [
             ('sepal length', 'float'),
             ('sepal width', 'float'),
diff --git a/examples/julia/config.py b/examples/julia/config.py
index f91f7aa..640978c 100644
--- a/examples/julia/config.py
+++ b/examples/julia/config.py
@@ -1,6 +1,6 @@
 {
     'dataset_loader_train': {
-        '__factory__': 'palladium.dataset.CSV',
+        '!': 'palladium.dataset.CSV',
         'path': 'iris.data',
         'names': [
             'sepal length',
@@ -15,7 +15,7 @@
     },
 
     'dataset_loader_test': {
-        '__factory__': 'palladium.dataset.CSV',
+        '!': 'palladium.dataset.CSV',
         'path': 'iris.data',
         'names': [
             'sepal length',
@@ -30,18 +30,18 @@
     },
 
     'model': {
-        '__factory__': 'palladium.julia.ClassificationModel',
+        '!': 'palladium.julia.ClassificationModel',
         'fit_func': 'SVM.svm',
         'predict_func': 'SVM.predict',
     },
 
     'model_persister': {
-        '__factory__': 'palladium.persistence.Database',
+        '!': 'palladium.persistence.Database',
         'url': 'sqlite:///iris-model.db',
     },
 
     'predict_service': {
-        '__factory__': 'palladium.server.PredictService',
+        '!': 'palladium.server.PredictService',
         'mapping': [
             ('sepal length', 'float'),
             ('sepal width', 'float'),
diff --git a/examples/keras/config.py b/examples/keras/config.py
new file mode 100644
index 0000000..436a8bf
--- /dev/null
+++ b/examples/keras/config.py
@@ -0,0 +1,51 @@
+{
+    'dataset_loader_train': {
+        '__factory__': 'palladium.dataset.Table',
+        'path': 'iris.data',
+        'names': [
+            'sepal length',
+            'sepal width',
+            'petal length',
+            'petal width',
+            'species',
+        ],
+        'target_column': 'species',
+        'sep': ',',
+        'nrows': 100,
+    },
+
+    'dataset_loader_test': {
+        '__copy__': 'dataset_loader_train',
+        'nrows': None,
+        'skiprows': 100,
+    },
+
+    'model': {
+        '__factory__': 'model.make_pipeline',
+        'epochs': 100,
+    },
+
+    'model_persister': {
+        '__factory__': 'palladium.persistence.Database',
+        'url': 'sqlite:///iris-model.db',
+    },
+
+    'predict_service': {
+        '__factory__': 'palladium.server.PredictService',
+        'mapping': [
+            ('sepal length', 'float'),
+            ('sepal width', 'float'),
+            ('petal length', 'float'),
+            ('petal width', 'float'),
+        ],
+    },
+
+    'service_metadata': {
+        'service_name': 'iris',
+        'service_version': '0.1',
+    },
+
+    'alive': {
+        'process_store_required': ('model',),
+    },
+}
diff --git a/examples/keras/iris.data b/examples/keras/iris.data
new file mode 100644
index 0000000..f0d63d9
--- /dev/null
+++ b/examples/keras/iris.data
@@ -0,0 +1,150 @@
+5.2,3.5,1.5,0.2,Iris-setosa
+4.3,3.0,1.1,0.1,Iris-setosa
+5.6,3.0,4.5,1.5,Iris-versicolor
+6.3,3.3,6.0,2.5,Iris-virginica
+5.1,3.8,1.5,0.3,Iris-setosa
+6.9,3.1,5.1,2.3,Iris-virginica
+7.7,3.0,6.1,2.3,Iris-virginica
+6.3,2.3,4.4,1.3,Iris-versicolor
+4.4,2.9,1.4,0.2,Iris-setosa
+7.2,3.2,6.0,1.8,Iris-virginica
+7.4,2.8,6.1,1.9,Iris-virginica
+7.7,2.8,6.7,2.0,Iris-virginica
+6.1,2.8,4.0,1.3,Iris-versicolor
+6.9,3.1,5.4,2.1,Iris-virginica
+5.6,2.9,3.6,1.3,Iris-versicolor
+6.5,3.2,5.1,2.0,Iris-virginica
+5.8,2.7,5.1,1.9,Iris-virginica
+7.1,3.0,5.9,2.1,Iris-virginica
+5.0,3.6,1.4,0.2,Iris-setosa
+5.0,2.3,3.3,1.0,Iris-versicolor
+6.5,3.0,5.2,2.0,Iris-virginica
+4.6,3.1,1.5,0.2,Iris-setosa
+6.1,2.9,4.7,1.4,Iris-versicolor
+6.9,3.1,4.9,1.5,Iris-versicolor
+4.9,2.5,4.5,1.7,Iris-virginica
+6.2,2.9,4.3,1.3,Iris-versicolor
+4.8,3.1,1.6,0.2,Iris-setosa
+5.7,2.8,4.1,1.3,Iris-versicolor
+5.8,2.7,4.1,1.0,Iris-versicolor
+6.5,3.0,5.8,2.2,Iris-virginica
+6.4,2.8,5.6,2.2,Iris-virginica
+5.5,3.5,1.3,0.2,Iris-setosa
+4.9,2.4,3.3,1.0,Iris-versicolor
+6.5,2.8,4.6,1.5,Iris-versicolor
+6.0,2.2,5.0,1.5,Iris-virginica
+5.1,3.8,1.6,0.2,Iris-setosa
+6.7,3.1,5.6,2.4,Iris-virginica
+5.0,3.4,1.6,0.4,Iris-setosa
+5.2,2.7,3.9,1.4,Iris-versicolor
+5.4,3.7,1.5,0.2,Iris-setosa
+5.3,3.7,1.5,0.2,Iris-setosa
+7.7,2.6,6.9,2.3,Iris-virginica
+6.8,2.8,4.8,1.4,Iris-versicolor
+5.2,4.1,1.5,0.1,Iris-setosa
+6.0,3.4,4.5,1.6,Iris-versicolor
+4.7,3.2,1.3,0.2,Iris-setosa
+7.2,3.6,6.1,2.5,Iris-virginica
+6.8,3.2,5.9,2.3,Iris-virginica
+6.3,2.8,5.1,1.5,Iris-virginica
+5.9,3.0,4.2,1.5,Iris-versicolor
+5.1,3.8,1.9,0.4,Iris-setosa
+5.0,3.3,1.4,0.2,Iris-setosa
+5.0,2.0,3.5,1.0,Iris-versicolor
+4.4,3.2,1.3,0.2,Iris-setosa
+6.3,2.5,5.0,1.9,Iris-virginica
+5.9,3.2,4.8,1.8,Iris-versicolor
+5.0,3.5,1.6,0.6,Iris-setosa
+5.4,3.0,4.5,1.5,Iris-versicolor
+6.7,3.1,4.7,1.5,Iris-versicolor
+5.7,2.5,5.0,2.0,Iris-virginica
+5.0,3.4,1.5,0.2,Iris-setosa
+5.8,2.7,3.9,1.2,Iris-versicolor
+6.1,2.8,4.7,1.2,Iris-versicolor
+4.5,2.3,1.3,0.3,Iris-setosa
+5.0,3.2,1.2,0.2,Iris-setosa
+5.4,3.9,1.7,0.4,Iris-setosa
+6.7,3.0,5.2,2.3,Iris-virginica
+6.6,2.9,4.6,1.3,Iris-versicolor
+6.0,2.2,4.0,1.0,Iris-versicolor
+6.7,3.0,5.0,1.7,Iris-versicolor
+7.0,3.2,4.7,1.4,Iris-versicolor
+5.6,2.5,3.9,1.1,Iris-versicolor
+4.9,3.0,1.4,0.2,Iris-setosa
+6.7,3.3,5.7,2.1,Iris-virginica
+5.4,3.4,1.5,0.4,Iris-setosa
+7.2,3.0,5.8,1.6,Iris-virginica
+5.5,2.4,3.8,1.1,Iris-versicolor
+5.7,3.8,1.7,0.3,Iris-setosa
+6.9,3.2,5.7,2.3,Iris-virginica
+6.2,3.4,5.4,2.3,Iris-virginica
+4.6,3.4,1.4,0.3,Iris-setosa
+6.4,3.2,5.3,2.3,Iris-virginica
+4.8,3.4,1.6,0.2,Iris-setosa
+6.7,3.3,5.7,2.5,Iris-virginica
+5.6,2.8,4.9,2.0,Iris-virginica
+4.4,3.0,1.3,0.2,Iris-setosa
+6.7,2.5,5.8,1.8,Iris-virginica
+6.4,3.2,4.5,1.5,Iris-versicolor
+5.8,2.7,5.1,1.9,Iris-virginica
+6.0,2.9,4.5,1.5,Iris-versicolor
+6.6,3.0,4.4,1.4,Iris-versicolor
+5.7,2.8,4.5,1.3,Iris-versicolor
+5.5,4.2,1.4,0.2,Iris-setosa
+5.8,2.8,5.1,2.4,Iris-virginica
+6.4,2.7,5.3,1.9,Iris-virginica
+5.7,2.9,4.2,1.3,Iris-versicolor
+6.4,2.9,4.3,1.3,Iris-versicolor
+5.0,3.5,1.3,0.3,Iris-setosa
+5.1,3.7,1.5,0.4,Iris-setosa
+5.7,3.0,4.2,1.2,Iris-versicolor
+6.5,3.0,5.5,1.8,Iris-virginica
+4.9,3.1,1.5,0.1,Iris-setosa
+6.3,3.4,5.6,2.4,Iris-virginica
+6.7,3.1,4.4,1.4,Iris-versicolor
+5.4,3.9,1.3,0.4,Iris-setosa
+5.5,2.6,4.4,1.2,Iris-versicolor
+4.8,3.0,1.4,0.3,Iris-setosa
+7.7,3.8,6.7,2.2,Iris-virginica
+6.3,3.3,4.7,1.6,Iris-versicolor
+6.0,3.0,4.8,1.8,Iris-virginica
+6.1,3.0,4.6,1.4,Iris-versicolor
+4.7,3.2,1.6,0.2,Iris-setosa
+7.3,2.9,6.3,1.8,Iris-virginica
+4.8,3.0,1.4,0.1,Iris-setosa
+6.1,3.0,4.9,1.8,Iris-virginica
+5.7,2.6,3.5,1.0,Iris-versicolor
+5.6,3.0,4.1,1.3,Iris-versicolor
+6.4,2.8,5.6,2.1,Iris-virginica
+6.3,2.9,5.6,1.8,Iris-virginica
+5.7,4.4,1.5,0.4,Iris-setosa
+6.1,2.6,5.6,1.4,Iris-virginica
+5.1,3.5,1.4,0.2,Iris-setosa
+5.9,3.0,5.1,1.8,Iris-virginica
+6.3,2.7,4.9,1.8,Iris-virginica
+5.5,2.5,4.0,1.3,Iris-versicolor
+5.5,2.3,4.0,1.3,Iris-versicolor
+4.6,3.6,1.0,0.2,Iris-setosa
+5.8,4.0,1.2,0.2,Iris-setosa
+5.1,2.5,3.0,1.1,Iris-versicolor
+5.2,3.4,1.4,0.2,Iris-setosa
+4.9,3.1,1.5,0.1,Iris-setosa
+5.0,3.0,1.6,0.2,Iris-setosa
+6.0,2.7,5.1,1.6,Iris-versicolor
+4.9,3.1,1.5,0.1,Iris-setosa
+5.8,2.6,4.0,1.2,Iris-versicolor
+6.8,3.0,5.5,2.1,Iris-virginica
+5.6,2.7,4.2,1.3,Iris-versicolor
+4.8,3.4,1.9,0.2,Iris-setosa
+6.2,2.8,4.8,1.8,Iris-virginica
+4.6,3.2,1.4,0.2,Iris-setosa
+6.2,2.2,4.5,1.5,Iris-versicolor
+5.1,3.3,1.7,0.5,Iris-setosa
+5.4,3.4,1.7,0.2,Iris-setosa
+5.1,3.4,1.5,0.2,Iris-setosa
+5.1,3.5,1.4,0.3,Iris-setosa
+7.6,3.0,6.6,2.1,Iris-virginica
+5.5,2.4,3.7,1.0,Iris-versicolor
+6.4,3.1,5.5,1.8,Iris-virginica
+7.9,3.8,6.4,2.0,Iris-virginica
+6.3,2.5,4.9,1.5,Iris-versicolor
diff --git a/examples/keras/model.py b/examples/keras/model.py
new file mode 100644
index 0000000..3905fac
--- /dev/null
+++ b/examples/keras/model.py
@@ -0,0 +1,33 @@
+from dstoolbox.pipeline import PipelineY
+from keras.models import Sequential
+from keras.layers import Dense
+from keras.wrappers.scikit_learn import KerasClassifier
+import numpy as np
+from sklearn.preprocessing import LabelBinarizer
+
+
+np.random.seed(0)
+
+
+def keras_model():
+    model = Sequential()
+    model.add(Dense(8, input_dim=4, activation='relu'))
+    model.add(Dense(3, activation='softmax'))
+    model.compile(
+        loss='categorical_crossentropy',
+        optimizer='adam',
+        metrics=['accuracy'],
+        )
+    return model
+
+
+def make_pipeline(**kw):
+    # In the case of this Iris dataset, our targets are string labels,
+    # and KerasClassifier doesn't like that.  So we transform the
+    # targets into a one-hot encoding instead using PipeLineY.
+    return PipelineY([
+            ('clf', KerasClassifier(build_fn=keras_model, **kw)),
+        ],
+        y_transformer=LabelBinarizer(),
+        predict_use_inverse=False,
+        )
diff --git a/examples/keras/requirements.txt b/examples/keras/requirements.txt
new file mode 100644
index 0000000..cdf759b
--- /dev/null
+++ b/examples/keras/requirements.txt
@@ -0,0 +1,3 @@
+dstoolbox
+Keras
+tensorflow
diff --git a/examples/xgboost/config.py b/examples/xgboost/config.py
new file mode 100644
index 0000000..39307ab
--- /dev/null
+++ b/examples/xgboost/config.py
@@ -0,0 +1,60 @@
+{
+    'dataset_loader_train': {
+        '__factory__': 'palladium.dataset.Table',
+        'path': 'iris.data',
+        'names': [
+            'sepal length',
+            'sepal width',
+            'petal length',
+            'petal width',
+            'species',
+        ],
+        'target_column': 'species',
+        'sep': ',',
+        'nrows': 100,
+    },
+
+    'dataset_loader_test': {
+        '__copy__': 'dataset_loader_train',
+        'nrows': None,
+        'skiprows': 100,
+    },
+
+    'model': {
+        '__factory__': 'xgboost.XGBClassifier',
+    },
+
+    'grid_search': {
+        'param_grid': {
+            'max_depth': [2, 3, 4],
+            'n_estimators': [3, 30, 300],
+        },
+        'cv': 8,
+        'verbose': 4,
+        'n_jobs': -1,
+    },
+
+    'model_persister': {
+        '__factory__': 'palladium.persistence.Database',
+        'url': 'sqlite:///iris-model.db',
+    },
+
+    'predict_service': {
+        '__factory__': 'palladium.server.PredictService',
+        'mapping': [
+            ('sepal length', 'float'),
+            ('sepal width', 'float'),
+            ('petal length', 'float'),
+            ('petal width', 'float'),
+        ],
+    },
+
+    'service_metadata': {
+        'service_name': 'iris',
+        'service_version': '0.1',
+    },
+
+    'alive': {
+        'process_store_required': ('model',),
+    },
+}
diff --git a/examples/xgboost/iris.data b/examples/xgboost/iris.data
new file mode 100644
index 0000000..f0d63d9
--- /dev/null
+++ b/examples/xgboost/iris.data
@@ -0,0 +1,150 @@
+5.2,3.5,1.5,0.2,Iris-setosa
+4.3,3.0,1.1,0.1,Iris-setosa
+5.6,3.0,4.5,1.5,Iris-versicolor
+6.3,3.3,6.0,2.5,Iris-virginica
+5.1,3.8,1.5,0.3,Iris-setosa
+6.9,3.1,5.1,2.3,Iris-virginica
+7.7,3.0,6.1,2.3,Iris-virginica
+6.3,2.3,4.4,1.3,Iris-versicolor
+4.4,2.9,1.4,0.2,Iris-setosa
+7.2,3.2,6.0,1.8,Iris-virginica
+7.4,2.8,6.1,1.9,Iris-virginica
+7.7,2.8,6.7,2.0,Iris-virginica
+6.1,2.8,4.0,1.3,Iris-versicolor
+6.9,3.1,5.4,2.1,Iris-virginica
+5.6,2.9,3.6,1.3,Iris-versicolor
+6.5,3.2,5.1,2.0,Iris-virginica
+5.8,2.7,5.1,1.9,Iris-virginica
+7.1,3.0,5.9,2.1,Iris-virginica
+5.0,3.6,1.4,0.2,Iris-setosa
+5.0,2.3,3.3,1.0,Iris-versicolor
+6.5,3.0,5.2,2.0,Iris-virginica
+4.6,3.1,1.5,0.2,Iris-setosa
+6.1,2.9,4.7,1.4,Iris-versicolor
+6.9,3.1,4.9,1.5,Iris-versicolor
+4.9,2.5,4.5,1.7,Iris-virginica
+6.2,2.9,4.3,1.3,Iris-versicolor
+4.8,3.1,1.6,0.2,Iris-setosa
+5.7,2.8,4.1,1.3,Iris-versicolor
+5.8,2.7,4.1,1.0,Iris-versicolor
+6.5,3.0,5.8,2.2,Iris-virginica
+6.4,2.8,5.6,2.2,Iris-virginica
+5.5,3.5,1.3,0.2,Iris-setosa
+4.9,2.4,3.3,1.0,Iris-versicolor
+6.5,2.8,4.6,1.5,Iris-versicolor
+6.0,2.2,5.0,1.5,Iris-virginica
+5.1,3.8,1.6,0.2,Iris-setosa
+6.7,3.1,5.6,2.4,Iris-virginica
+5.0,3.4,1.6,0.4,Iris-setosa
+5.2,2.7,3.9,1.4,Iris-versicolor
+5.4,3.7,1.5,0.2,Iris-setosa
+5.3,3.7,1.5,0.2,Iris-setosa
+7.7,2.6,6.9,2.3,Iris-virginica
+6.8,2.8,4.8,1.4,Iris-versicolor
+5.2,4.1,1.5,0.1,Iris-setosa
+6.0,3.4,4.5,1.6,Iris-versicolor
+4.7,3.2,1.3,0.2,Iris-setosa
+7.2,3.6,6.1,2.5,Iris-virginica
+6.8,3.2,5.9,2.3,Iris-virginica
+6.3,2.8,5.1,1.5,Iris-virginica
+5.9,3.0,4.2,1.5,Iris-versicolor
+5.1,3.8,1.9,0.4,Iris-setosa
+5.0,3.3,1.4,0.2,Iris-setosa
+5.0,2.0,3.5,1.0,Iris-versicolor
+4.4,3.2,1.3,0.2,Iris-setosa
+6.3,2.5,5.0,1.9,Iris-virginica
+5.9,3.2,4.8,1.8,Iris-versicolor
+5.0,3.5,1.6,0.6,Iris-setosa
+5.4,3.0,4.5,1.5,Iris-versicolor
+6.7,3.1,4.7,1.5,Iris-versicolor
+5.7,2.5,5.0,2.0,Iris-virginica
+5.0,3.4,1.5,0.2,Iris-setosa
+5.8,2.7,3.9,1.2,Iris-versicolor
+6.1,2.8,4.7,1.2,Iris-versicolor
+4.5,2.3,1.3,0.3,Iris-setosa
+5.0,3.2,1.2,0.2,Iris-setosa
+5.4,3.9,1.7,0.4,Iris-setosa
+6.7,3.0,5.2,2.3,Iris-virginica
+6.6,2.9,4.6,1.3,Iris-versicolor
+6.0,2.2,4.0,1.0,Iris-versicolor
+6.7,3.0,5.0,1.7,Iris-versicolor
+7.0,3.2,4.7,1.4,Iris-versicolor
+5.6,2.5,3.9,1.1,Iris-versicolor
+4.9,3.0,1.4,0.2,Iris-setosa
+6.7,3.3,5.7,2.1,Iris-virginica
+5.4,3.4,1.5,0.4,Iris-setosa
+7.2,3.0,5.8,1.6,Iris-virginica
+5.5,2.4,3.8,1.1,Iris-versicolor
+5.7,3.8,1.7,0.3,Iris-setosa
+6.9,3.2,5.7,2.3,Iris-virginica
+6.2,3.4,5.4,2.3,Iris-virginica
+4.6,3.4,1.4,0.3,Iris-setosa
+6.4,3.2,5.3,2.3,Iris-virginica
+4.8,3.4,1.6,0.2,Iris-setosa
+6.7,3.3,5.7,2.5,Iris-virginica
+5.6,2.8,4.9,2.0,Iris-virginica
+4.4,3.0,1.3,0.2,Iris-setosa
+6.7,2.5,5.8,1.8,Iris-virginica
+6.4,3.2,4.5,1.5,Iris-versicolor
+5.8,2.7,5.1,1.9,Iris-virginica
+6.0,2.9,4.5,1.5,Iris-versicolor
+6.6,3.0,4.4,1.4,Iris-versicolor
+5.7,2.8,4.5,1.3,Iris-versicolor
+5.5,4.2,1.4,0.2,Iris-setosa
+5.8,2.8,5.1,2.4,Iris-virginica
+6.4,2.7,5.3,1.9,Iris-virginica
+5.7,2.9,4.2,1.3,Iris-versicolor
+6.4,2.9,4.3,1.3,Iris-versicolor
+5.0,3.5,1.3,0.3,Iris-setosa
+5.1,3.7,1.5,0.4,Iris-setosa
+5.7,3.0,4.2,1.2,Iris-versicolor
+6.5,3.0,5.5,1.8,Iris-virginica
+4.9,3.1,1.5,0.1,Iris-setosa
+6.3,3.4,5.6,2.4,Iris-virginica
+6.7,3.1,4.4,1.4,Iris-versicolor
+5.4,3.9,1.3,0.4,Iris-setosa
+5.5,2.6,4.4,1.2,Iris-versicolor
+4.8,3.0,1.4,0.3,Iris-setosa
+7.7,3.8,6.7,2.2,Iris-virginica
+6.3,3.3,4.7,1.6,Iris-versicolor
+6.0,3.0,4.8,1.8,Iris-virginica
+6.1,3.0,4.6,1.4,Iris-versicolor
+4.7,3.2,1.6,0.2,Iris-setosa
+7.3,2.9,6.3,1.8,Iris-virginica
+4.8,3.0,1.4,0.1,Iris-setosa
+6.1,3.0,4.9,1.8,Iris-virginica
+5.7,2.6,3.5,1.0,Iris-versicolor
+5.6,3.0,4.1,1.3,Iris-versicolor
+6.4,2.8,5.6,2.1,Iris-virginica
+6.3,2.9,5.6,1.8,Iris-virginica
+5.7,4.4,1.5,0.4,Iris-setosa
+6.1,2.6,5.6,1.4,Iris-virginica
+5.1,3.5,1.4,0.2,Iris-setosa
+5.9,3.0,5.1,1.8,Iris-virginica
+6.3,2.7,4.9,1.8,Iris-virginica
+5.5,2.5,4.0,1.3,Iris-versicolor
+5.5,2.3,4.0,1.3,Iris-versicolor
+4.6,3.6,1.0,0.2,Iris-setosa
+5.8,4.0,1.2,0.2,Iris-setosa
+5.1,2.5,3.0,1.1,Iris-versicolor
+5.2,3.4,1.4,0.2,Iris-setosa
+4.9,3.1,1.5,0.1,Iris-setosa
+5.0,3.0,1.6,0.2,Iris-setosa
+6.0,2.7,5.1,1.6,Iris-versicolor
+4.9,3.1,1.5,0.1,Iris-setosa
+5.8,2.6,4.0,1.2,Iris-versicolor
+6.8,3.0,5.5,2.1,Iris-virginica
+5.6,2.7,4.2,1.3,Iris-versicolor
+4.8,3.4,1.9,0.2,Iris-setosa
+6.2,2.8,4.8,1.8,Iris-virginica
+4.6,3.2,1.4,0.2,Iris-setosa
+6.2,2.2,4.5,1.5,Iris-versicolor
+5.1,3.3,1.7,0.5,Iris-setosa
+5.4,3.4,1.7,0.2,Iris-setosa
+5.1,3.4,1.5,0.2,Iris-setosa
+5.1,3.5,1.4,0.3,Iris-setosa
+7.6,3.0,6.6,2.1,Iris-virginica
+5.5,2.4,3.7,1.0,Iris-versicolor
+6.4,3.1,5.5,1.8,Iris-virginica
+7.9,3.8,6.4,2.0,Iris-virginica
+6.3,2.5,4.9,1.5,Iris-versicolor
diff --git a/examples/xgboost/requirements.txt b/examples/xgboost/requirements.txt
new file mode 100644
index 0000000..10ddd5b
--- /dev/null
+++ b/examples/xgboost/requirements.txt
@@ -0,0 +1 @@
+xgboost
diff --git a/palladium/config.py b/palladium/config.py
index 295a538..2829515 100644
--- a/palladium/config.py
+++ b/palladium/config.py
@@ -38,7 +38,7 @@ def __getitem__(self, name):
 
 
 class ComponentHandler:
-    key = '__factory__'
+    key = '!'
 
     def __init__(self, config):
         self.config = config
@@ -63,6 +63,10 @@ def finish(self):
                 component.initialize_component(self.config)
 
 
+class ComponentHandler2(ComponentHandler):
+    key = '__factory__'
+
+
 class CopyHandler:
     key = '__copy__'
 
@@ -131,9 +135,24 @@ def __call__(self, name, props):
         return props
 
 
+def rewrite_handler(key_from, key_to):
+    class RewriteHandler:
+        key = key_from
+        target = key_to
+
+        def __init__(self, config):
+            pass
+
+        def __call__(self, name, props):
+            props[self.target] = props.pop(self.key)
+            return props
+    return RewriteHandler
+
+
 def _handlers_phase0(configs):
     return {
         Handler.key: Handler(configs) for Handler in [
+            rewrite_handler('__factory__', '!'),
             CopyHandler,
             ]
         }
diff --git a/palladium/persistence.py b/palladium/persistence.py
index a106313..53820b4 100644
--- a/palladium/persistence.py
+++ b/palladium/persistence.py
@@ -183,7 +183,7 @@ def read(self, version=None):
         if version is None:
             props = self.list_properties()
             if 'active-model' not in props:
-                raise LookupError("No active model available")
+                raise LookupError("No active model available: " + self.path)
             version = props['active-model']
 
         fname = self.path.format(version=version) + '.pkl.gz'
@@ -196,7 +196,17 @@ def read(self, version=None):
 
         with self.io.open(fname, 'rb') as fh:
             with gzip.open(fh, 'rb') as f:
-                return pickle.load(f)
+                model = pickle.load(f)
+
+        attachments = annotate(model).get('__attachments__', [])
+        for key in attachments:
+            fname_attach = self.attach_filename(version=version, key=key)
+            if self.io.exists(fname_attach):
+                with open(fname_attach, 'rb') as f:
+                    data_attach = base64.b64encode(f.read())
+                    annotate(model, {key: data_attach})
+
+        return model
 
     def write(self, model):
         last_version = 0
@@ -207,11 +217,29 @@ def write(self, model):
         version = last_version + 1
         li.append(annotate(model, {'version': version}))
 
+        annotations = annotate(model)
+        attachments = {
+            key: data
+            for key, data in annotations.items()
+            if key.startswith('attachments/')
+            }
+        if attachments:
+            for key in attachments:
+                del annotations[key]
+            annotations['__attachments__'] = tuple(attachments.keys())
+        annotate(model, annotations)
+
         fname = self.path.format(version=version) + '.pkl.gz'
         with self.io.open(fname, 'wb') as fh:
             with gzip.open(fh, 'wb') as f:
                 pickle.dump(model, f)
 
+        if attachments:
+            for key, data in attachments.items():
+                fname_attach = self.attach_filename(version=version, key=key)
+                with self.io.open(fname_attach, 'wb') as f:
+                    f.write(base64.b64decode(data))
+
         self._update_md({'models': li})
         return version
 
@@ -230,19 +258,33 @@ def activate(self, version):
         self._update_md({'properties': md['properties']})
 
     def delete(self, version):
-        md = self._read_md()
-        versions = [m['version'] for m in md['models']]
         version = int(version)
-        if version not in versions:
+        md = self._read_md()
+        try:
+            model_md = [m for m in md['models'] if m['version'] == version][0]
+        except IndexError:
             raise LookupError("No such version: {}".format(version))
+
         self._update_md({
             'models': [m for m in md['models'] if m['version'] != version]})
         self.io.remove(self.path.format(version=version) + '.pkl.gz')
 
+        attachments = model_md.get('__attachments__', [])
+        for key in attachments:
+            fname_attach = self.attach_filename(version=version, key=key)
+            if self.io.exists(fname_attach):
+                self.io.remove(fname_attach)
+
     @property
     def _md_filename(self):
         return self.path.format(version='metadata') + '.json'
 
+    def attach_filename(self, version, key):
+        return (
+            self.path.format(version=version) +
+            '-{}'.format(key[len('attachments/'):])
+            )
+
     def _read_md(self):
         if self.io.exists(self._md_filename):
             with self.io.open(self._md_filename, 'r') as f:
@@ -670,6 +712,8 @@ def __init__(self, **kwargs):
         self.fs = s3fs.S3FileSystem(anon=False)
 
     def open(self, path, mode='r'):
+        # this is needed to avoid reading stale metadata JSONs
+        self.fs.invalidate_cache()
         return self.fs.open(path, mode=mode)
 
     def exists(self, path):
@@ -688,9 +732,9 @@ class S3(FileLike):
     persister. For example, if you used the ``File`` persister
     before, change your config as follows:
 
-        -   '__factory__': 'palladium.persistence.File',
+        -   '!': 'palladium.persistence.File',
         -   'path': 'models/mymodel-{version}',
-        +   '__factory__': 'palladium.persistence.S3',
+        +   '!': 'palladium.persistence.S3',
         +   'path': 'your-s3-bucket/models/mymodel-{version}',
 
     Note that the first part of the path denotes the s3 bucket.
diff --git a/palladium/server.py b/palladium/server.py
index 1257b6c..2ce446a 100644
--- a/palladium/server.py
+++ b/palladium/server.py
@@ -35,7 +35,7 @@ def make_ujson_response(obj, status_code=200):
     :return:
       A Flask response.
     """
-    json_encoded = ujson.encode(obj, ensure_ascii=False, double_precision=-1)
+    json_encoded = ujson.encode(obj, ensure_ascii=False)
     resp = make_response(json_encoded)
     resp.mimetype = 'application/json'
     resp.content_type = 'application/json; charset=utf-8'
diff --git a/palladium/tests/test_config.py b/palladium/tests/test_config.py
index b8b1f25..f8efe4e 100644
--- a/palladium/tests/test_config.py
+++ b/palladium/tests/test_config.py
@@ -86,7 +86,7 @@ def config1_fname(self, tmpdir):
             'env': environ['ENV1'],
             'here': here,
             'blocking': {
-                '__factory__': 'palladium.tests.test_config.BlockingDummy',
+                '!': 'palladium.tests.test_config.BlockingDummy',
             }
         }""")
         return str(path)
@@ -102,7 +102,7 @@ def config3_fname(self, tmpdir):
         path = tmpdir.join('config3.py')
         path.write("""{
             'bad': {
-                '__factory__': 'palladium.tests.test_config.BadDummy'
+                '!': 'palladium.tests.test_config.BadDummy'
              }
         }""")
         return str(path)
@@ -169,14 +169,14 @@ def config1(self):
         dummy = 'palladium.tests.test_config.MyDummyComponent'
         return {
             'mycomponent': {
-                '__factory__': dummy,
+                '!': dummy,
                 'arg1': 3,
                 'arg2': {'no': 'factory'},
                 'subcomponent': {
-                    '__factory__': dummy,
+                    '!': dummy,
                     'arg1': {
                         'subsubcomponent': {
-                            '__factory__':
+                            '!':
                             dummy,
                             'arg1': 'wobwob',
                             'arg2': 9,
@@ -186,16 +186,16 @@ def config1(self):
                     },
                 },
             'mylistofcomponents': [{
-                '__factory__': dummy,
+                '!': dummy,
                 'arg1': 'wobwob',
                 },
                 'somethingelse',
                 ],
             'mynestedlistofcomponents': [[{
-                '__factory__': dummy,
+                '!': dummy,
                 'arg1': 'feep',
                 'arg2': {
-                    '__factory__': dummy,
+                    '__factory__': dummy,  # alternative to '!'
                     'arg1': 6,
                 },
             }]],
@@ -214,7 +214,7 @@ def config1(self):
                 },
 
             '__python__': """
-C['mynestedlistofcomponents'][0][0]['arg2']['__factory__'] = 'builtins:dict'
+C['mynestedlistofcomponents'][0][0]['arg2']['!'] = 'builtins:dict'
 C['myotherconstant'] = 13
 """,
             }
diff --git a/palladium/tests/test_fit.py b/palladium/tests/test_fit.py
index 5890e35..e7f0b43 100644
--- a/palladium/tests/test_fit.py
+++ b/palladium/tests/test_fit.py
@@ -438,7 +438,6 @@ def estimator(self):
             LogisticRegression(solver='liblinear'),
             param_grid={'C': [0.001, 0.01]},
             cv=3,
-            iid=False,
             )
 
     @pytest.mark.parametrize('backend', ['threading', 'sequential'])
diff --git a/palladium/tests/test_persistence.py b/palladium/tests/test_persistence.py
index e50f9b3..6672449 100644
--- a/palladium/tests/test_persistence.py
+++ b/palladium/tests/test_persistence.py
@@ -13,6 +13,8 @@
 import requests_mock
 import pytest
 
+from palladium.interfaces import annotate
+
 
 class Dummy:
     def __init__(self, **kwargs):
@@ -74,12 +76,14 @@ def test_read(self, File):
             patch('palladium.persistence.File.list_properties') as lp,\
             patch('palladium.persistence.os.path.exists') as exists,\
             patch('palladium.persistence.open') as open,\
+            patch('palladium.persistence.annotate') as annotate,\
             patch('palladium.persistence.gzip.open') as gzopen,\
             patch('palladium.persistence.pickle.load') as load:
             lm.return_value = [{'version': 99}]
             lp.return_value = {'active-model': '99'}
             exists.side_effect = lambda fn: fn == '/models/model-99.pkl.gz'
             open.return_value = MagicMock()
+            annotate.return_value = {}
             result = File('/models/model-{version}').read()
             open.assert_called_with('/models/model-99.pkl.gz', 'rb')
             assert result == load.return_value
@@ -89,11 +93,13 @@ def test_read_with_version(self, File):
         with patch('palladium.persistence.File.list_models') as lm,\
             patch('palladium.persistence.os.path.exists') as exists,\
             patch('palladium.persistence.open') as open,\
+            patch('palladium.persistence.annotate') as annotate,\
             patch('palladium.persistence.gzip.open') as gzopen,\
             patch('palladium.persistence.pickle.load') as load:
             lm.return_value = [{'version': 99}]
             exists.side_effect = lambda fn: fn == '/models/model-432.pkl.gz'
             open.return_value = MagicMock()
+            annotate.return_value = {}
             result = File('/models/model-{version}').read(432)
             open.assert_called_with('/models/model-432.pkl.gz', 'rb')
             assert result == load.return_value
@@ -104,20 +110,22 @@ def test_read_no_model(self, File):
             patch('palladium.persistence.File.list_properties') as lp:
             lp.return_value = {}
             lm.return_value = []
-            f = File('/models/model-{version}')
+            filename = '/models/model-{version}'
+            f = File(filename)
             with pytest.raises(LookupError) as exc:
                 f.read()
-            assert exc.value.args[0] == 'No active model available'
+            assert exc.value.args[0] == 'No active model available: {}'.format(filename)
 
     def test_read_no_active_model(self, File):
         with patch('palladium.persistence.File.list_models') as lm,\
             patch('palladium.persistence.File.list_properties') as lp:
             lp.return_value = {}
             lm.return_value = [{'version': 99}]
-            f = File('/models/model-{version}')
+            filename = '/models/model-{version}'
+            f = File(filename)
             with pytest.raises(LookupError) as exc:
                 f.read()
-            assert exc.value.args[0] == 'No active model available'
+            assert exc.value.args[0] == 'No active model available: {}'.format(filename)
 
     def test_read_no_model_with_given_version(self, File):
         with patch('palladium.persistence.os.path.exists') as exists:
@@ -385,6 +393,69 @@ def test_upgrade_1_0_no_metadata(self, File):
             dump.assert_called_with(new_md, open_rv, indent=4)
 
 
+class TestFileAttachments:
+    @pytest.fixture
+    def persister(self, tmpdir):
+        from palladium.persistence import File
+        model1 = Dummy()
+        annotate(model1, {'attachments/myatt.txt': 'aGV5',
+                          'attachments/my2ndatt.txt': 'aG8='})
+        model2 = Dummy()
+        annotate(model2, {'attachments/myatt.txt': 'aG8='})
+        persister = File(str(tmpdir) + '/model-{version}')
+        persister.write(model1)
+        persister.write(model2)
+        return persister
+
+    def test_filenames(self, persister, tmpdir):
+        # Attachment files are namespaced by the model:
+        assert sorted(os.listdir(tmpdir)) == [
+            'model-1-my2ndatt.txt', 'model-1-myatt.txt', 'model-1.pkl.gz',
+            'model-2-myatt.txt', 'model-2.pkl.gz',
+            'model-metadata.json',
+            ]
+
+    def test_attachment_file_contents(self, persister, tmpdir):
+        # Attachment data is written to files system decoded:
+        with open(tmpdir + '/model-1-myatt.txt', 'rb') as f:
+            assert f.read() == b'hey'
+        with open(tmpdir + '/model-1-my2ndatt.txt', 'rb') as f:
+            assert f.read() == b'ho'
+        with open(tmpdir + '/model-2-myatt.txt', 'rb') as f:
+            assert f.read() == b'ho'
+
+    def test_attachment_not_in_metadata_file(self, persister, tmpdir):
+        # Attachment data is not written to the metadata file:
+        with open(tmpdir + '/model-metadata.json') as f:
+            md = json.loads(f.read())
+            assert len(md['models']) == 2
+            for model_md in md['models']:
+                assert 'attachments/myatt.txt' not in model_md
+
+    def test_attachment_not_in_pickle(self, persister, tmpdir):
+        # Attachment data is not pickled as part of the model:
+        with open(tmpdir + '/model-1.pkl.gz', 'rb') as fh:
+            with gzip.open(fh, 'rb') as f:
+                model1 = pickle.load(f)
+                assert 'attachments/myatt.txt' not in annotate(model1)
+
+    def test_loaded_back_on_read(self, persister, tmpdir):
+        # Attachment is read back from the file into metadata
+        # dictionary on read:
+        model1 = persister.read(version=1)
+        assert annotate(model1)['attachments/myatt.txt'] == b'aGV5'
+        assert annotate(model1)['attachments/my2ndatt.txt'] == b'aG8='
+
+    def test_deleted_on_delete(self, persister, tmpdir):
+        # Attachment files are removed from the file system when a
+        # model is deleted:
+        persister.delete(1)
+        assert sorted(os.listdir(tmpdir)) == [
+            'model-2-myatt.txt', 'model-2.pkl.gz',
+            'model-metadata.json',
+            ]
+
+
 class TestDatabase:
     @pytest.fixture
     def Database(self):
@@ -665,7 +736,7 @@ def handle_put_md(request, context):
 
     def test_download(self, mocked_requests, persister):
         """ test download and activation of a model """
-        expected = Dummy(name='mymodel')
+        expected = Dummy(name='mymodel', __metadata__={})
         zipped_model = gzip.compress(pickle.dumps(expected))
 
         get_md_url = "%s/mymodel-metadata.json" % (self.base_url,)
diff --git a/palladium/tests/test_server.py b/palladium/tests/test_server.py
index 2062b3c..86f5d7d 100644
--- a/palladium/tests/test_server.py
+++ b/palladium/tests/test_server.py
@@ -320,7 +320,7 @@ def test_entry_point_not_set(
 
         config['model_persister'] = Mock()
         config['predict_service'] = {
-            '__factory__': 'palladium.server.PredictService',
+            '!': 'palladium.server.PredictService',
             'mapping': [
                 ('param', 'str'),
             ],
@@ -342,14 +342,14 @@ def test_entry_point_multiple(
 
         config['model_persister'] = Mock()
         config['my_predict_service'] = {
-            '__factory__': 'palladium.server.PredictService',
+            '!': 'palladium.server.PredictService',
             'mapping': [
                 ('param', 'str'),
             ],
             'entry_point': '/predict1',
         }
         config['my_predict_service2'] = {
-            '__factory__': 'palladium.server.PredictService',
+            '!': 'palladium.server.PredictService',
             'mapping': [
                 ('param', 'str'),
             ],
@@ -381,14 +381,14 @@ def test_entry_point_multiple_conflict(
 
         config['model_persister'] = Mock()
         config['my_predict_service'] = {
-            '__factory__': 'palladium.server.PredictService',
+            '!': 'palladium.server.PredictService',
             'mapping': [
                 ('param', 'str'),
             ],
             'entry_point': '/predict1',  # <--
         }
         config['my_predict_service2'] = {
-            '__factory__': 'palladium.server.PredictService',
+            '!': 'palladium.server.PredictService',
             'mapping': [
                 ('param', 'str'),
             ],
@@ -665,7 +665,7 @@ def test_it(self, fit, config, jobs, flask_app):
         config['model_persister'] = model_persister
         with flask_app.test_request_context(method='POST'):
             resp = fit()
-        sleep(0.02)
+        sleep(0.05)
         resp_json = json.loads(resp.get_data(as_text=True))
         job = jobs[resp_json['job_id']]
         assert job['status'] == 'finished'
diff --git a/palladium/tests/test_util.py b/palladium/tests/test_util.py
index a584c3f..c6fb99c 100644
--- a/palladium/tests/test_util.py
+++ b/palladium/tests/test_util.py
@@ -424,12 +424,12 @@ def myfunc(tts):
 
         num_threads_before = len(threading.enumerate())
         for i in range(3):
-            run_job(myfunc, tts=i/100)
+            run_job(myfunc, tts=5*i/100)
 
         job1, job2, job3 = sorted(jobs.values(), key=lambda x: x['started'])
 
         samples = []
-        for i in range(10):
+        for i in range(50):
             samples.append((
                 job1['status'],
                 job2['status'],
diff --git a/requirements-dev.txt b/requirements-dev.txt
index 13b14ba..a74eca6 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -1,6 +1,6 @@
 cov-core==1.15.0
-coverage==4.5.4
-pluggy==0.12.0
-pytest==5.0.1
-pytest-cov==2.7.1
-requests-mock==1.6.0
+coverage==5.1
+pluggy==0.13.1
+pytest==5.4.1
+pytest-cov==2.8.1
+requests-mock==1.8.0
diff --git a/requirements.txt b/requirements.txt
index 651e5c0..6cc5941 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,24 +1,24 @@
-certifi==2019.6.16
+certifi==2020.4.5.1
 chardet==3.0.4
-Click==7.0
+Click==7.1.2
 docopt==0.6.2
-Flask==1.1.1
-idna==2.8
+Flask==1.1.2
+idna==2.9
 itsdangerous==1.1.0
-Jinja2==2.10.1
-joblib==0.13.2
+Jinja2==2.11.2
+joblib==0.14.1
 MarkupSafe==1.1.1
-numpy==1.17.0
-pandas==0.24.2
-psutil==5.6.3
-python-dateutil==2.8.0
-pytz==2019.2
-requests==2.22.0
-scikit-learn==0.21.3
-scipy==1.3.0
-six==1.12.0
-SQLAlchemy==1.3.6
-ujson==1.35
-urllib3==1.25.3
-Werkzeug==0.15.5
+numpy==1.18.4
+pandas==1.0.3
+psutil==5.7.0
+python-dateutil==2.8.1
+pytz==2020.1
+requests==2.23.0
+scikit-learn==0.22.2.post1
+scipy==1.4.1
+six==1.14.0
+SQLAlchemy==1.3.16
+ujson==2.0.3
+urllib3==1.25.9
+Werkzeug==1.0.1
 # julia==0.4.5
diff --git a/setup.py b/setup.py
index a96ed66..65a17e2 100644
--- a/setup.py
+++ b/setup.py
@@ -23,8 +23,8 @@
     ]
 
 docs_require = [
-    'julia',
-    'rpy2',
+    # 'julia',
+    # 'rpy2',
     'Sphinx',
     'sphinx_rtd_theme',
     ]