http://git-wip-us.apache.org/repos/asf/incubator-ariatosca/blob/fb3ac003/aria/storage/modeling/orchestrator_elements.py
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diff --git a/aria/storage/modeling/orchestrator_elements.py 
b/aria/storage/modeling/orchestrator_elements.py
new file mode 100644
index 0000000..a7ed5e9
--- /dev/null
+++ b/aria/storage/modeling/orchestrator_elements.py
@@ -0,0 +1,461 @@
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""
+Aria's storage.models module
+Path: aria.storage.models
+
+models module holds aria's models.
+
+classes:
+    * Field - represents a single field.
+    * IterField - represents an iterable field.
+    * Model - abstract model implementation.
+    * Snapshot - snapshots implementation model.
+    * Deployment - deployment implementation model.
+    * DeploymentUpdateStep - deployment update step implementation model.
+    * DeploymentUpdate - deployment update implementation model.
+    * DeploymentModification - deployment modification implementation model.
+    * Execution - execution implementation model.
+    * Node - node implementation model.
+    * Relationship - relationship implementation model.
+    * NodeInstance - node instance implementation model.
+    * RelationshipInstance - relationship instance implementation model.
+    * Plugin - plugin implementation model.
+"""
+from collections import namedtuple
+from datetime import datetime
+
+from sqlalchemy import (
+    Column,
+    Integer,
+    Text,
+    DateTime,
+    Boolean,
+    Enum,
+    String,
+    Float,
+    orm,
+)
+from sqlalchemy.ext.associationproxy import association_proxy
+from sqlalchemy.ext.declarative import declared_attr
+
+from aria.orchestrator.exceptions import TaskAbortException, TaskRetryException
+
+from .type import List, Dict
+from .structure import ModelMixin
+
+__all__ = (
+    'ServiceInstanceUpdateStepBase',
+    'ServiceInstanceUpdateBase',
+    'ServiceInstanceModificationBase',
+    'Execution',
+    'PluginBase',
+    'TaskBase'
+)
+
+# pylint: disable=no-self-argument, no-member, abstract-method
+
+
+class Execution(ModelMixin):
+    """
+    Execution model representation.
+    """
+    # Needed only for pylint. the id will be populated by sqlalcehmy and the 
proper column.
+    __tablename__ = 'execution'
+
+    TERMINATED = 'terminated'
+    FAILED = 'failed'
+    CANCELLED = 'cancelled'
+    PENDING = 'pending'
+    STARTED = 'started'
+    CANCELLING = 'cancelling'
+    FORCE_CANCELLING = 'force_cancelling'
+
+    STATES = [TERMINATED, FAILED, CANCELLED, PENDING, STARTED, CANCELLING, 
FORCE_CANCELLING]
+    END_STATES = [TERMINATED, FAILED, CANCELLED]
+    ACTIVE_STATES = [state for state in STATES if state not in END_STATES]
+
+    VALID_TRANSITIONS = {
+        PENDING: [STARTED, CANCELLED],
+        STARTED: END_STATES + [CANCELLING],
+        CANCELLING: END_STATES + [FORCE_CANCELLING]
+    }
+
+    @orm.validates('status')
+    def validate_status(self, key, value):
+        """Validation function that verifies execution status transitions are 
OK"""
+        try:
+            current_status = getattr(self, key)
+        except AttributeError:
+            return
+        valid_transitions = self.VALID_TRANSITIONS.get(current_status, [])
+        if all([current_status is not None,
+                current_status != value,
+                value not in valid_transitions]):
+            raise ValueError('Cannot change execution status from {current} to 
{new}'.format(
+                current=current_status,
+                new=value))
+        return value
+
+    created_at = Column(DateTime, index=True)
+    started_at = Column(DateTime, nullable=True, index=True)
+    ended_at = Column(DateTime, nullable=True, index=True)
+    error = Column(Text, nullable=True)
+    is_system_workflow = Column(Boolean, nullable=False, default=False)
+    parameters = Column(Dict)
+    status = Column(Enum(*STATES, name='execution_status'), default=PENDING)
+    workflow_name = Column(Text)
+
+    @declared_attr
+    def service_template(cls):
+        return association_proxy('service_instance', 'service_template')
+
+    @declared_attr
+    def service_instance_fk(cls):
+        return cls.foreign_key('service_instance')
+
+    @declared_attr
+    def service_instance(cls):
+        return cls.many_to_one_relationship('service_instance')
+
+    @declared_attr
+    def service_instance_name(cls):
+        return association_proxy('service_instance', cls.name_column_name())
+
+    @declared_attr
+    def service_template_name(cls):
+        return association_proxy('service_instance', 'service_template_name')
+
+    def __str__(self):
+        return '<{0} id=`{1}` (status={2})>'.format(
+            self.__class__.__name__,
+            getattr(self, self.name_column_name()),
+            self.status
+        )
+
+
+class ServiceInstanceUpdateBase(ModelMixin):
+    """
+    Deployment update model representation.
+    """
+    # Needed only for pylint. the id will be populated by sqlalcehmy and the 
proper column.
+    steps = None
+
+    __tablename__ = 'service_instance_update'
+
+    _private_fields = ['execution_fk', 'deployment_fk']
+
+    created_at = Column(DateTime, nullable=False, index=True)
+    deployment_plan = Column(Dict, nullable=False)
+    deployment_update_node_instances = Column(Dict)
+    deployment_update_deployment = Column(Dict)
+    deployment_update_nodes = Column(List)
+    modified_entity_ids = Column(Dict)
+    state = Column(Text)
+
+    @declared_attr
+    def execution_fk(cls):
+        return cls.foreign_key('execution', nullable=True)
+
+    @declared_attr
+    def execution(cls):
+        return cls.many_to_one_relationship('execution')
+
+    @declared_attr
+    def execution_name(cls):
+        return association_proxy('execution', cls.name_column_name())
+
+    @declared_attr
+    def service_instance_fk(cls):
+        return cls.foreign_key('service_instance')
+
+    @declared_attr
+    def service_instance(cls):
+        return cls.many_to_one_relationship('service_instance')
+
+    @declared_attr
+    def service_instance_name(cls):
+        return association_proxy('service_instance', cls.name_column_name())
+
+    def to_dict(self, suppress_error=False, **kwargs):
+        dep_update_dict = super(ServiceInstanceUpdateBase, 
self).to_dict(suppress_error)     #pylint: disable=no-member
+        # Taking care of the fact the DeploymentSteps are _BaseModels
+        dep_update_dict['steps'] = [step.to_dict() for step in self.steps]
+        return dep_update_dict
+
+
+class ServiceInstanceUpdateStepBase(ModelMixin):
+    """
+    Deployment update step model representation.
+    """
+    # Needed only for pylint. the id will be populated by sqlalcehmy and the 
proper column.
+    __tablename__ = 'service_instance_update_step'
+    _private_fields = ['deployment_update_fk']
+
+    _action_types = namedtuple('ACTION_TYPES', 'ADD, REMOVE, MODIFY')
+    ACTION_TYPES = _action_types(ADD='add', REMOVE='remove', MODIFY='modify')
+    _entity_types = namedtuple(
+        'ENTITY_TYPES',
+        'NODE, RELATIONSHIP, PROPERTY, OPERATION, WORKFLOW, OUTPUT, 
DESCRIPTION, GROUP, '
+        'POLICY_TYPE, POLICY_TRIGGER, PLUGIN')
+    ENTITY_TYPES = _entity_types(
+        NODE='node',
+        RELATIONSHIP='relationship',
+        PROPERTY='property',
+        OPERATION='operation',
+        WORKFLOW='workflow',
+        OUTPUT='output',
+        DESCRIPTION='description',
+        GROUP='group',
+        POLICY_TYPE='policy_type',
+        POLICY_TRIGGER='policy_trigger',
+        PLUGIN='plugin'
+    )
+
+    action = Column(Enum(*ACTION_TYPES, name='action_type'), nullable=False)
+    entity_id = Column(Text, nullable=False)
+    entity_type = Column(Enum(*ENTITY_TYPES, name='entity_type'), 
nullable=False)
+
+    @declared_attr
+    def service_instance_update_fk(cls):
+        return cls.foreign_key('service_instance_update')
+
+    @declared_attr
+    def deployment_update(cls):
+        return cls.many_to_one_relationship('service_instance_update',
+                                            backreference='steps')
+
+    @declared_attr
+    def deployment_update_name(cls):
+        return association_proxy('deployment_update', cls.name_column_name())
+
+    def __hash__(self):
+        return hash((getattr(self, self.id_column_name()), self.entity_id))
+
+    def __lt__(self, other):
+        """
+        the order is 'remove' < 'modify' < 'add'
+        :param other:
+        :return:
+        """
+        if not isinstance(other, self.__class__):
+            return not self >= other
+
+        if self.action != other.action:
+            if self.action == 'remove':
+                return_value = True
+            elif self.action == 'add':
+                return_value = False
+            else:
+                return_value = other.action == 'add'
+            return return_value
+
+        if self.action == 'add':
+            return self.entity_type == 'node' and other.entity_type == 
'relationship'
+        if self.action == 'remove':
+            return self.entity_type == 'relationship' and other.entity_type == 
'node'
+        return False
+
+
+class ServiceInstanceModificationBase(ModelMixin):
+    """
+    Deployment modification model representation.
+    """
+    __tablename__ = 'service_instance_modification'
+    _private_fields = ['deployment_fk']
+
+    STARTED = 'started'
+    FINISHED = 'finished'
+    ROLLEDBACK = 'rolledback'
+
+    STATES = [STARTED, FINISHED, ROLLEDBACK]
+    END_STATES = [FINISHED, ROLLEDBACK]
+
+    context = Column(Dict)
+    created_at = Column(DateTime, nullable=False, index=True)
+    ended_at = Column(DateTime, index=True)
+    modified_nodes = Column(Dict)
+    node_instances = Column(Dict)
+    status = Column(Enum(*STATES, name='deployment_modification_status'))
+
+    @declared_attr
+    def service_instance_fk(cls):
+        return cls.foreign_key('service_instance')
+
+    @declared_attr
+    def service_instance(cls):
+        return cls.many_to_one_relationship('service_instance',
+                                            backreference='modifications')
+
+    @declared_attr
+    def deployment_name(cls):
+        return association_proxy('service_instance', cls.name_column_name())
+
+
+class PluginBase(ModelMixin):
+    """
+    Plugin model representation.
+    """
+    __tablename__ = 'plugin'
+
+    archive_name = Column(Text, nullable=False, index=True)
+    distribution = Column(Text)
+    distribution_release = Column(Text)
+    distribution_version = Column(Text)
+    package_name = Column(Text, nullable=False, index=True)
+    package_source = Column(Text)
+    package_version = Column(Text)
+    supported_platform = Column(Text)
+    supported_py_versions = Column(List)
+    uploaded_at = Column(DateTime, nullable=False, index=True)
+    wheels = Column(List, nullable=False)
+
+
+class TaskBase(ModelMixin):
+    """
+    A Model which represents an task
+    """
+    __tablename__ = 'task'
+    _private_fields = ['node_instance_fk', 'relationship_instance_fk', 
'execution_fk']
+
+    @declared_attr
+    def node_fk(cls):
+        return cls.foreign_key('node', nullable=True)
+
+    @declared_attr
+    def node_name(cls):
+        return association_proxy('node', cls.name_column_name())
+
+    @declared_attr
+    def node(cls):
+        return cls.many_to_one_relationship('node')
+
+    @declared_attr
+    def relationship_fk(cls):
+        return cls.foreign_key('relationship', nullable=True)
+
+    @declared_attr
+    def relationship_name(cls):
+        return association_proxy('relationships', cls.name_column_name())
+
+    @declared_attr
+    def relationship(cls):
+        return cls.many_to_one_relationship('relationship')
+
+    @declared_attr
+    def plugin_fk(cls):
+        return cls.foreign_key('plugin', nullable=True)
+
+    @declared_attr
+    def plugin(cls):
+        return cls.many_to_one_relationship('plugin')
+
+    @declared_attr
+    def execution_fk(cls):
+        return cls.foreign_key('execution', nullable=True)
+
+    @declared_attr
+    def execution(cls):
+        return cls.many_to_one_relationship('execution')
+
+    @declared_attr
+    def execution_name(cls):
+        return association_proxy('execution', cls.name_column_name())
+
+    PENDING = 'pending'
+    RETRYING = 'retrying'
+    SENT = 'sent'
+    STARTED = 'started'
+    SUCCESS = 'success'
+    FAILED = 'failed'
+    STATES = (
+        PENDING,
+        RETRYING,
+        SENT,
+        STARTED,
+        SUCCESS,
+        FAILED,
+    )
+
+    WAIT_STATES = [PENDING, RETRYING]
+    END_STATES = [SUCCESS, FAILED]
+
+    RUNS_ON_SOURCE = 'source'
+    RUNS_ON_TARGET = 'target'
+    RUNS_ON_NODE_INSTANCE = 'node_instance'
+    RUNS_ON = (RUNS_ON_NODE_INSTANCE, RUNS_ON_SOURCE, RUNS_ON_TARGET)
+
+    @orm.validates('max_attempts')
+    def validate_max_attempts(self, _, value):                                 
 # pylint: disable=no-self-use
+        """Validates that max attempts is either -1 or a positive number"""
+        if value < 1 and value != TaskBase.INFINITE_RETRIES:
+            raise ValueError('Max attempts can be either -1 (infinite) or any 
positive number. '
+                             'Got {value}'.format(value=value))
+        return value
+
+    INFINITE_RETRIES = -1
+
+    status = Column(Enum(*STATES, name='status'), default=PENDING)
+
+    due_at = Column(DateTime, default=datetime.utcnow)
+    started_at = Column(DateTime, default=None)
+    ended_at = Column(DateTime, default=None)
+    max_attempts = Column(Integer, default=1)
+    retry_count = Column(Integer, default=0)
+    retry_interval = Column(Float, default=0)
+    ignore_failure = Column(Boolean, default=False)
+
+    # Operation specific fields
+    implementation = Column(String)
+    inputs = Column(Dict)
+    # This is unrelated to the plugin of the task. This field is related to 
the plugin name
+    # received from the blueprint.
+    plugin_name = Column(String)
+    _runs_on = Column(Enum(*RUNS_ON, name='runs_on'), name='runs_on')
+
+    @property
+    def runs_on(self):
+        if self._runs_on == self.RUNS_ON_NODE_INSTANCE:
+            return self.node
+        elif self._runs_on == self.RUNS_ON_SOURCE:
+            return self.relationship.source_node  # pylint: disable=no-member
+        elif self._runs_on == self.RUNS_ON_TARGET:
+            return self.relationship.target_node  # pylint: disable=no-member
+        return None
+
+    @property
+    def actor(self):
+        """
+        Return the actor of the task
+        :return:
+        """
+        return self.node or self.relationship
+
+    @classmethod
+    def as_node_instance(cls, instance, runs_on, **kwargs):
+        return cls(node=instance, _runs_on=runs_on, **kwargs)
+
+    @classmethod
+    def as_relationship_instance(cls, instance, runs_on, **kwargs):
+        return cls(relationship=instance, _runs_on=runs_on, **kwargs)
+
+    @staticmethod
+    def abort(message=None):
+        raise TaskAbortException(message)
+
+    @staticmethod
+    def retry(message=None, retry_interval=None):
+        raise TaskRetryException(message, retry_interval=retry_interval)

http://git-wip-us.apache.org/repos/asf/incubator-ariatosca/blob/fb3ac003/aria/storage/modeling/structure.py
----------------------------------------------------------------------
diff --git a/aria/storage/modeling/structure.py 
b/aria/storage/modeling/structure.py
new file mode 100644
index 0000000..386887e
--- /dev/null
+++ b/aria/storage/modeling/structure.py
@@ -0,0 +1,320 @@
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""
+Aria's storage.structures module
+Path: aria.storage.structures
+
+models module holds aria's models.
+
+classes:
+    * Field - represents a single field.
+    * IterField - represents an iterable field.
+    * PointerField - represents a single pointer field.
+    * IterPointerField - represents an iterable pointers field.
+    * Model - abstract model implementation.
+"""
+
+from sqlalchemy.orm import relationship, backref
+from sqlalchemy.ext import associationproxy
+from sqlalchemy import (
+    Column,
+    ForeignKey,
+    Integer,
+    Text,
+    Table,
+)
+
+from . import utils
+
+
+class Function(object):
+    """
+    An intrinsic function.
+
+    Serves as a placeholder for a value that should eventually be derived
+    by calling the function.
+    """
+
+    @property
+    def as_raw(self):
+        raise NotImplementedError
+
+    def _evaluate(self, context, container):
+        raise NotImplementedError
+
+    def __deepcopy__(self, memo):
+        # Circumvent cloning in order to maintain our state
+        return self
+
+
+class ElementBase(object):
+    """
+    Base class for :class:`ServiceInstance` elements.
+
+    All elements support validation, diagnostic dumping, and representation as
+    raw data (which can be translated into JSON or YAML) via :code:`as_raw`.
+    """
+
+    @property
+    def as_raw(self):
+        raise NotImplementedError
+
+    def validate(self, context):
+        pass
+
+    def coerce_values(self, context, container, report_issues):
+        pass
+
+    def dump(self, context):
+        pass
+
+
+class ModelElementBase(ElementBase):
+    """
+    Base class for :class:`ServiceModel` elements.
+
+    All model elements can be instantiated into :class:`ServiceInstance` 
elements.
+    """
+
+    def instantiate(self, context, container):
+        raise NotImplementedError
+
+
+class ModelMixin(ModelElementBase):
+
+    @utils.classproperty
+    def __modelname__(cls):                                                    
                     # pylint: disable=no-self-argument
+        return getattr(cls, '__mapiname__', cls.__tablename__)
+
+    @classmethod
+    def id_column_name(cls):
+        raise NotImplementedError
+
+    @classmethod
+    def name_column_name(cls):
+        raise NotImplementedError
+
+    @classmethod
+    def _get_cls_by_tablename(cls, tablename):
+        """Return class reference mapped to table.
+
+         :param tablename: String with name of table.
+         :return: Class reference or None.
+         """
+        if tablename in (cls.__name__, cls.__tablename__):
+            return cls
+
+        for table_cls in cls._decl_class_registry.values():
+            if tablename == getattr(table_cls, '__tablename__', None):
+                return table_cls
+
+    @classmethod
+    def foreign_key(cls, table_name, nullable=False):
+        """Return a ForeignKey object with the relevant
+
+        :param table: Unique id column in the parent table
+        :param nullable: Should the column be allowed to remain empty
+        """
+        return Column(Integer,
+                      
ForeignKey('{tablename}.id'.format(tablename=table_name), ondelete='CASCADE'),
+                      nullable=nullable)
+
+    @classmethod
+    def one_to_one_relationship(cls, table_name, backreference=None):
+        return relationship(lambda: cls._get_cls_by_tablename(table_name),
+                            backref=backref(backreference or 
cls.__tablename__, uselist=False))
+
+    @classmethod
+    def many_to_one_relationship(cls,
+                                 parent_table_name,
+                                 foreign_key_column=None,
+                                 backreference=None,
+                                 backref_kwargs=None,
+                                 **kwargs):
+        """Return a one-to-many SQL relationship object
+        Meant to be used from inside the *child* object
+
+        :param parent_class: Class of the parent table
+        :param cls: Class of the child table
+        :param foreign_key_column: The column of the foreign key (from the 
child table)
+        :param backreference: The name to give to the reference to the child 
(on the parent table)
+        """
+        relationship_kwargs = kwargs
+        if foreign_key_column:
+            relationship_kwargs.setdefault('foreign_keys', getattr(cls, 
foreign_key_column))
+
+        backref_kwargs = backref_kwargs or {}
+        backref_kwargs.setdefault('lazy', 'dynamic')
+        # The following line make sure that when the *parent* is
+        #  deleted, all its connected children are deleted as well
+        backref_kwargs.setdefault('cascade', 'all')
+
+        return relationship(lambda: 
cls._get_cls_by_tablename(parent_table_name),
+                            backref=backref(backreference or 
utils.pluralize(cls.__tablename__),
+                                            **backref_kwargs or {}),
+                            **relationship_kwargs)
+
+    @classmethod
+    def relationship_to_self(cls, local_column):
+
+        remote_side_str = '{cls.__name__}.{remote_column}'.format(
+            cls=cls,
+            remote_column=cls.id_column_name()
+        )
+        primaryjoin_str = '{remote_side_str} == 
{cls.__name__}.{local_column}'.format(
+            remote_side_str=remote_side_str,
+            cls=cls,
+            local_column=local_column)
+        return 
relationship(cls._get_cls_by_tablename(cls.__tablename__).__name__,
+                            primaryjoin=primaryjoin_str,
+                            remote_side=remote_side_str,
+                            post_update=True)
+
+    @classmethod
+    def many_to_many_relationship(cls, other_table_name, table_prefix, 
relationship_kwargs=None):
+        """Return a many-to-many SQL relationship object
+
+        Notes:
+        1. The backreference name is the current table's table name
+        2. This method creates a new helper table in the DB
+
+        :param cls: The class of the table we're connecting from
+        :param other_table_name: The class of the table we're connecting to
+        :param table_prefix: Custom prefix for the helper table name and the
+        backreference name
+        """
+        current_table_name = cls.__tablename__
+        current_column_name = '{0}_id'.format(current_table_name)
+        current_foreign_key = '{0}.id'.format(current_table_name)
+
+        other_column_name = '{0}_id'.format(other_table_name)
+        other_foreign_key = '{0}.id'.format(other_table_name)
+
+        helper_table_name = '{0}_{1}'.format(current_table_name, 
other_table_name)
+
+        backref_name = current_table_name
+        if table_prefix:
+            helper_table_name = '{0}_{1}'.format(table_prefix, 
helper_table_name)
+            backref_name = '{0}_{1}'.format(table_prefix, backref_name)
+
+        secondary_table = cls.get_secondary_table(
+            cls.metadata,
+            helper_table_name,
+            current_column_name,
+            other_column_name,
+            current_foreign_key,
+            other_foreign_key
+        )
+
+        return relationship(
+            lambda: cls._get_cls_by_tablename(other_table_name),
+            secondary=secondary_table,
+            backref=backref(backref_name),
+            **(relationship_kwargs or {})
+        )
+
+    @staticmethod
+    def get_secondary_table(metadata,
+                            helper_table_name,
+                            first_column_name,
+                            second_column_name,
+                            first_foreign_key,
+                            second_foreign_key):
+        """Create a helper table for a many-to-many relationship
+
+        :param helper_table_name: The name of the table
+        :param first_column_name: The name of the first column in the table
+        :param second_column_name: The name of the second column in the table
+        :param first_foreign_key: The string representing the first foreign 
key,
+        for example `blueprint.storage_id`, or `tenants.id`
+        :param second_foreign_key: The string representing the second foreign 
key
+        :return: A Table object
+        """
+        return Table(
+            helper_table_name,
+            metadata,
+            Column(
+                first_column_name,
+                Integer,
+                ForeignKey(first_foreign_key)
+            ),
+            Column(
+                second_column_name,
+                Integer,
+                ForeignKey(second_foreign_key)
+            )
+        )
+
+    def to_dict(self, fields=None, suppress_error=False):
+        """Return a dict representation of the model
+
+        :param suppress_error: If set to True, sets `None` to attributes that
+        it's unable to retrieve (e.g., if a relationship wasn't established
+        yet, and so it's impossible to access a property through it)
+        """
+        res = dict()
+        fields = fields or self.fields()
+        for field in fields:
+            try:
+                field_value = getattr(self, field)
+            except AttributeError:
+                if suppress_error:
+                    field_value = None
+                else:
+                    raise
+            if isinstance(field_value, list):
+                field_value = list(field_value)
+            elif isinstance(field_value, dict):
+                field_value = dict(field_value)
+            elif isinstance(field_value, ModelMixin):
+                field_value = field_value.to_dict()
+            res[field] = field_value
+
+        return res
+
+    @classmethod
+    def _association_proxies(cls):
+        for col, value in vars(cls).items():
+            if isinstance(value, associationproxy.AssociationProxy):
+                yield col
+
+    @classmethod
+    def fields(cls):
+        """Return the list of field names for this table
+
+        Mostly for backwards compatibility in the code (that uses `fields`)
+        """
+        fields = set(cls._association_proxies())
+        fields.update(cls.__table__.columns.keys())
+        return fields - set(getattr(cls, '_private_fields', []))
+
+    def __repr__(self):
+        return '<{__class__.__name__} id=`{id}`>'.format(
+            __class__=self.__class__,
+            id=getattr(self, self.name_column_name()))
+
+
+class ModelIDMixin(object):
+    id = Column(Integer, primary_key=True, autoincrement=True)
+    name = Column(Text, nullable=True, index=True)
+
+    @classmethod
+    def id_column_name(cls):
+        return 'id'
+
+    @classmethod
+    def name_column_name(cls):
+        return 'name'

http://git-wip-us.apache.org/repos/asf/incubator-ariatosca/blob/fb3ac003/aria/storage/modeling/template_elements.py
----------------------------------------------------------------------
diff --git a/aria/storage/modeling/template_elements.py 
b/aria/storage/modeling/template_elements.py
new file mode 100644
index 0000000..17cc292
--- /dev/null
+++ b/aria/storage/modeling/template_elements.py
@@ -0,0 +1,1348 @@
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+from copy import deepcopy
+from types import FunctionType
+
+from sqlalchemy import (
+    Column,
+    Text,
+    Integer,
+    DateTime,
+    Boolean,
+)
+from sqlalchemy.ext.associationproxy import association_proxy
+from sqlalchemy.ext.declarative import declared_attr
+
+from aria.parser import validation
+from aria.utils import collections, formatting, console
+
+from . import (
+    utils,
+    instance_elements,
+    structure,
+    type as aria_type
+)
+
+# pylint: disable=no-self-argument, no-member, abstract-method
+
+
+# region Element templates
+
+
+class ServiceTemplateBase(structure.ModelMixin):
+
+    __tablename__ = 'service_template'
+
+    description = Column(Text)
+    metadata = Column(Text)
+
+    # region orchestrator required columns
+
+    created_at = Column(DateTime, nullable=False, index=True)
+    main_file_name = Column(Text)
+    plan = Column(aria_type.Dict)
+    updated_at = Column(DateTime)
+
+    # endregion
+
+    # region foreign keys
+    @declared_attr
+    def substitution_template_fk(cls):
+        return cls.foreign_key('substitution_template', nullable=True)
+
+    # endregion
+
+    # region one-to-one relationships
+    @declared_attr
+    def substitution_template(cls):
+        return cls.one_to_one_relationship('substitution_template')
+    # endregion
+
+    # region many-to-many relationships
+
+    @declared_attr
+    def inputs(cls):
+        return cls.many_to_many_relationship('parameter', 
table_prefix='inputs')
+
+    @declared_attr
+    def outputs(cls):
+        return cls.many_to_many_relationship('parameter', 
table_prefix='outputs')
+
+    # endregion
+
+    @property
+    def as_raw(self):
+        return collections.OrderedDict((
+            ('description', self.description),
+            ('metadata', formatting.as_raw(self.metadata)),
+            ('node_templates', formatting.as_raw_list(self.node_templates)),
+            ('group_templates', formatting.as_raw_list(self.group_templates)),
+            ('policy_templates', 
formatting.as_raw_list(self.policy_templates)),
+            ('substitution_template', 
formatting.as_raw(self.substitution_template)),
+            ('inputs', formatting.as_raw_dict(self.inputs)),
+            ('outputs', formatting.as_raw_dict(self.outputs)),
+            ('operation_templates', 
formatting.as_raw_list(self.operation_templates))))
+
+    def instantiate(self, context, container):
+        service_instance = instance_elements.ServiceInstanceBase()
+        context.modeling.instance = service_instance
+
+        service_instance.description = deepcopy_with_locators(self.description)
+
+        if self.metadata is not None:
+            service_instance.metadata = self.metadata.instantiate(context, 
container)
+
+        for node_template in self.node_templates.itervalues():
+            for _ in range(node_template.default_instances):
+                node = node_template.instantiate(context, container)
+                service_instance.nodes[node.id] = node
+
+        utils.instantiate_dict(context, self, service_instance.groups, 
self.group_templates)
+        utils.instantiate_dict(context, self, service_instance.policies, 
self.policy_templates)
+        utils.instantiate_dict(context, self, service_instance.operations, 
self.operation_templates)
+
+        if self.substitution_template is not None:
+            service_instance.substitution = 
self.substitution_template.instantiate(context,
+                                                                               
    container)
+
+        utils.instantiate_dict(context, self, service_instance.inputs, 
self.inputs)
+        utils.instantiate_dict(context, self, service_instance.outputs, 
self.outputs)
+
+        for name, the_input in context.modeling.inputs.iteritems():
+            if name not in service_instance.inputs:
+                context.validation.report('input "%s" is not supported' % name)
+            else:
+                service_instance.inputs[name].value = the_input
+
+        return service_instance
+
+    def validate(self, context):
+        if self.metadata is not None:
+            self.metadata.validate(context)
+        utils.validate_dict_values(context, self.node_templates)
+        utils.validate_dict_values(context, self.group_templates)
+        utils.validate_dict_values(context, self.policy_templates)
+        if self.substitution_template is not None:
+            self.substitution_template.validate(context)
+        utils.validate_dict_values(context, self.inputs)
+        utils.validate_dict_values(context, self.outputs)
+        utils.validate_dict_values(context, self.operation_templates)
+
+    def coerce_values(self, context, container, report_issues):
+        if self.metadata is not None:
+            self.metadata.coerce_values(context, container, report_issues)
+        utils.coerce_dict_values(context, container, self.node_templates, 
report_issues)
+        utils.coerce_dict_values(context, container, self.group_templates, 
report_issues)
+        utils.coerce_dict_values(context, container, self.policy_templates, 
report_issues)
+        if self.substitution_template is not None:
+            self.substitution_template.coerce_values(context, container, 
report_issues)
+        utils.coerce_dict_values(context, container, self.inputs, 
report_issues)
+        utils.coerce_dict_values(context, container, self.outputs, 
report_issues)
+        utils.coerce_dict_values(context, container, self.operation_templates, 
report_issues)
+
+    def dump(self, context):
+        if self.description is not None:
+            console.puts(context.style.meta(self.description))
+        if self.metadata is not None:
+            self.metadata.dump(context)
+        for node_template in self.node_templates.itervalues():
+            node_template.dump(context)
+        for group_template in self.group_templates.itervalues():
+            group_template.dump(context)
+        for policy_template in self.policy_templates.itervalues():
+            policy_template.dump(context)
+        if self.substitution_template is not None:
+            self.substitution_template.dump(context)
+        dump_parameters(context, self.inputs, 'Inputs')
+        dump_parameters(context, self.outputs, 'Outputs')
+        utils.dump_dict_values(context, self.operation_templates, 'Operation 
templates')
+
+
+class InterfaceTemplateBase(structure.ModelMixin):
+    __tablename__ = 'interface_template'
+    # region foreign keys
+
+    @declared_attr
+    def node_template_fk(cls):
+        return cls.foreign_key('node_template', nullable=True)
+
+    @declared_attr
+    def group_template_fk(cls):
+        return cls.foreign_key('group_template', nullable=True)
+
+    # endregion
+
+    description = Column(Text)
+    type_name = Column(Text)
+
+    # region many-to-one relationship
+    @declared_attr
+    def node_template(cls):
+        return cls.many_to_one_relationship('node_template')
+
+    @declared_attr
+    def group_template(cls):
+        return cls.many_to_one_relationship('group_template')
+
+    # endregion
+
+    # region many-to-many relationships
+
+    @declared_attr
+    def inputs(cls):
+        return cls.many_to_many_relationship('parameter', 
table_prefix='inputs')
+
+    @declared_attr
+    def properties(cls):
+        return cls.many_to_many_relationship('parameter', 
table_prefix='properties')
+    # endregion
+
+    @property
+    def as_raw(self):
+        return collections.OrderedDict((
+            ('name', self.name),
+            ('description', self.description),
+            ('type_name', self.type_name),
+            ('inputs', formatting.as_raw_dict(self.properties)),  # pylint: 
disable=no-member
+            # TODO fix self.properties reference
+            ('operation_templates', 
formatting.as_raw_list(self.operation_templates))))
+
+    def instantiate(self, context, container):
+        interface = instance_elements.InterfaceBase(self.name, self.type_name)
+        interface.description = deepcopy_with_locators(self.description)
+        utils.instantiate_dict(context, container, interface.inputs, 
self.inputs)
+        utils.instantiate_dict(context, container, interface.operations, 
self.operation_templates)
+        return interface
+
+    def validate(self, context):
+        if self.type_name:
+            if context.modeling.interface_types.get_descendant(self.type_name) 
is None:
+                context.validation.report('interface "%s" has an unknown type: 
%s'
+                                          % (self.name, 
formatting.safe_repr(self.type_name)),
+                                          level=validation.Issue.BETWEEN_TYPES)
+
+        utils.validate_dict_values(context, self.inputs)
+        utils.validate_dict_values(context, self.operation_templates)
+
+    def coerce_values(self, context, container, report_issues):
+        utils.coerce_dict_values(context, container, self.inputs, 
report_issues)
+        utils.coerce_dict_values(context, container, self.operation_templates, 
report_issues)
+
+    def dump(self, context):
+        console.puts(context.style.node(self.name))
+        if self.description:
+            console.puts(context.style.meta(self.description))
+        with context.style.indent:
+            console.puts('Interface type: %s' % 
context.style.type(self.type_name))
+            dump_parameters(context, self.inputs, 'Inputs')
+            utils.dump_dict_values(context, self.operation_templates, 
'Operation templates')
+
+
+class OperationTemplateBase(structure.ModelMixin):
+    __tablename__ = 'operation_template'
+
+    # region foreign keys
+
+    @declared_attr
+    def service_template_fk(cls):
+        return cls.foreign_key('service_template', nullable=True)
+
+    @declared_attr
+    def interface_template_fk(cls):
+        return cls.foreign_key('interface_template', nullable=True)
+
+    # endregion
+
+    description = Column(Text)
+    implementation = Column(Text)
+    dependencies = Column(aria_type.StrictList(item_cls=basestring))
+    executor = Column(Text)
+    max_retries = Column(Integer)
+    retry_interval = Column(Integer)
+
+    # region orchestrator required columns
+    plugin = Column(Text)
+    operation = Column(Boolean)
+
+    # region many-to-one relationships
+    @declared_attr
+    def service_template(cls):
+        return cls.many_to_one_relationship('service_template')
+
+    @declared_attr
+    def interface_template(cls):
+        return cls.many_to_one_relationship('interface_template')
+    # endregion
+
+    # region many-to-many relationships
+
+    @declared_attr
+    def inputs(cls):
+        return cls.many_to_many_relationship('parameter', 
table_prefix='inputs')
+
+    # endregion
+
+    @property
+    def as_raw(self):
+        return collections.OrderedDict((
+            ('name', self.name),
+            ('description', self.description),
+            ('implementation', self.implementation),
+            ('dependencies', self.dependencies),
+            ('executor', self.executor),
+            ('max_retries', self.max_retries),
+            ('retry_interval', self.retry_interval),
+            ('inputs', formatting.as_raw_dict(self.inputs))))
+
+    def instantiate(self, context, container):
+        operation = instance_elements.OperationBase(self.name)
+        operation.description = deepcopy_with_locators(self.description)
+        operation.implementation = self.implementation
+        operation.dependencies = self.dependencies
+        operation.executor = self.executor
+        operation.max_retries = self.max_retries
+        operation.retry_interval = self.retry_interval
+        utils.instantiate_dict(context, container, operation.inputs, 
self.inputs)
+        return operation
+
+    def validate(self, context):
+        utils.validate_dict_values(context, self.inputs)
+
+    def coerce_values(self, context, container, report_issues):
+        utils.coerce_dict_values(context, container, self.inputs, 
report_issues)
+
+    def dump(self, context):
+        console.puts(context.style.node(self.name))
+        if self.description:
+            console.puts(context.style.meta(self.description))
+        with context.style.indent:
+            if self.implementation is not None:
+                console.puts('Implementation: %s' % 
context.style.literal(self.implementation))
+            if self.dependencies:
+                console.puts('Dependencies: %s' % ', '.join(
+                    (str(context.style.literal(v)) for v in 
self.dependencies)))
+            if self.executor is not None:
+                console.puts('Executor: %s' % 
context.style.literal(self.executor))
+            if self.max_retries is not None:
+                console.puts('Max retries: %s' % 
context.style.literal(self.max_retries))
+            if self.retry_interval is not None:
+                console.puts('Retry interval: %s' % 
context.style.literal(self.retry_interval))
+            dump_parameters(context, self.inputs, 'Inputs')
+
+
+class ArtifactTemplateBase(structure.ModelMixin):
+    """
+    A file associated with a :class:`NodeTemplate`.
+
+    Properties:
+
+    * :code:`name`: Name
+    * :code:`description`: Description
+    * :code:`type_name`: Must be represented in the :class:`ModelingContext`
+    * :code:`source_path`: Source path (CSAR or repository)
+    * :code:`target_path`: Path at destination machine
+    * :code:`repository_url`: Repository URL
+    * :code:`repository_credential`: Dict of string
+    * :code:`properties`: Dict of :class:`Parameter`
+    """
+    __tablename__ = 'artifact_template'
+    # region foreign keys
+
+    @declared_attr
+    def node_template_fk(cls):
+        return cls.foreign_key('node_template')
+
+    # endregion
+
+    description = Column(Text)
+    type_name = Column(Text)
+    source_path = Column(Text)
+    target_path = Column(Text)
+    repository_url = Column(Text)
+    repository_credential = Column(aria_type.StrictDict(basestring, 
basestring))
+
+    # region many-to-one relationship
+    @declared_attr
+    def node_template(cls):
+        return cls.many_to_one_relationship('node_template')
+    # endregion
+
+    # region many-to-many relationships
+
+    @declared_attr
+    def properties(cls):
+        return cls.many_to_many_relationship('parameter', 
table_prefix='properties')
+
+    # endregion
+
+    @property
+    def as_raw(self):
+        return collections.OrderedDict((
+            ('name', self.name),
+            ('description', self.description),
+            ('type_name', self.type_name),
+            ('source_path', self.source_path),
+            ('target_path', self.target_path),
+            ('repository_url', self.repository_url),
+            ('repository_credential', 
formatting.as_agnostic(self.repository_credential)),
+            ('properties', 
formatting.as_raw_dict(self.properties.iteritems()))))
+
+    def instantiate(self, context, container):
+        artifact = instance_elements.ArtifactBase(self.name, self.type_name, 
self.source_path)
+        artifact.description = deepcopy_with_locators(self.description)
+        artifact.target_path = self.target_path
+        artifact.repository_url = self.repository_url
+        artifact.repository_credential = self.repository_credential
+        utils.instantiate_dict(context, container, artifact.properties, 
self.properties)
+        return artifact
+
+    def validate(self, context):
+        if context.modeling.artifact_types.get_descendant(self.type_name) is 
None:
+            context.validation.report('artifact "%s" has an unknown type: %s'
+                                      % (self.name, 
formatting.safe_repr(self.type_name)),
+                                      level=validation.Issue.BETWEEN_TYPES)
+
+        utils.validate_dict_values(context, self.properties)
+
+    def coerce_values(self, context, container, report_issues):
+        utils.coerce_dict_values(context, container, self.properties, 
report_issues)
+
+    def dump(self, context):
+        console.puts(context.style.node(self.name))
+        if self.description:
+            console.puts(context.style.meta(self.description))
+        with context.style.indent:
+            console.puts('Artifact type: %s' % 
context.style.type(self.type_name))
+            console.puts('Source path: %s' % 
context.style.literal(self.source_path))
+            if self.target_path is not None:
+                console.puts('Target path: %s' % 
context.style.literal(self.target_path))
+            if self.repository_url is not None:
+                console.puts('Repository URL: %s' % 
context.style.literal(self.repository_url))
+            if self.repository_credential:
+                console.puts('Repository credential: %s'
+                             % 
context.style.literal(self.repository_credential))
+            dump_parameters(context, self.properties)
+
+
+class PolicyTemplateBase(structure.ModelMixin):
+    """
+    Policies can be applied to zero or more :class:`NodeTemplate` or 
:class:`GroupTemplate`
+    instances.
+
+    Properties:
+
+    * :code:`name`: Name
+    * :code:`description`: Description
+    * :code:`type_name`: Must be represented in the :class:`ModelingContext`
+    * :code:`properties`: Dict of :class:`Parameter`
+    * :code:`target_node_template_names`: Must be represented in the 
:class:`ServiceModel`
+    * :code:`target_group_template_names`: Must be represented in the 
:class:`ServiceModel`
+    """
+    __tablename__ = 'policy_template'
+    # region foreign keys
+    @declared_attr
+    def service_template_fk(cls):
+        return cls.foreign_key('service_template')
+
+    @declared_attr
+    def group_template_fk(cls):
+        return cls.foreign_key('group_template')
+
+    # endregion
+
+    description = Column(Text)
+    type_name = Column(Text)
+    target_node_template_names = Column(aria_type.StrictList(basestring))
+    target_group_template_names = Column(aria_type.StrictList(basestring))
+
+    # region many-to-one relationship
+    @declared_attr
+    def service_template(cls):
+        return cls.many_to_one_relationship('service_template')
+
+    @declared_attr
+    def group_template(cls):
+        return cls.many_to_one_relationship('group_template')
+
+    # endregion
+
+    # region many-to-many relationships
+
+    @declared_attr
+    def properties(cls):
+        return cls.many_to_many_relationship('parameter', 
table_prefix='properties')
+
+    # endregion
+
+    @property
+    def as_raw(self):
+        return collections.OrderedDict((
+            ('name', self.name),
+            ('description', self.description),
+            ('type_name', self.type_name),
+            ('properties', formatting.as_raw_dict(self.properties)),
+            ('target_node_template_names', self.target_node_template_names),
+            ('target_group_template_names', self.target_group_template_names)))
+
+    def instantiate(self, context, *args, **kwargs):
+        policy = instance_elements.PolicyBase(self.name, self.type_name)
+        utils.instantiate_dict(context, self, policy.properties, 
self.properties)
+        for node_template_name in self.target_node_template_names:
+            policy.target_node_ids.extend(
+                context.modeling.instance.get_node_ids(node_template_name))
+        for group_template_name in self.target_group_template_names:
+            policy.target_group_ids.extend(
+                context.modeling.instance.get_group_ids(group_template_name))
+        return policy
+
+    def validate(self, context):
+        if context.modeling.policy_types.get_descendant(self.type_name) is 
None:
+            context.validation.report('policy template "%s" has an unknown 
type: %s'
+                                      % (self.name, 
formatting.safe_repr(self.type_name)),
+                                      level=validation.Issue.BETWEEN_TYPES)
+
+        utils.validate_dict_values(context, self.properties)
+
+    def coerce_values(self, context, container, report_issues):
+        utils.coerce_dict_values(context, self, self.properties, report_issues)
+
+    def dump(self, context):
+        console.puts('Policy template: %s' % context.style.node(self.name))
+        if self.description:
+            console.puts(context.style.meta(self.description))
+        with context.style.indent:
+            console.puts('Type: %s' % context.style.type(self.type_name))
+            dump_parameters(context, self.properties)
+            if self.target_node_template_names:
+                console.puts('Target node templates: %s' % ', '.join(
+                    (str(context.style.node(v)) for v in 
self.target_node_template_names)))
+            if self.target_group_template_names:
+                console.puts('Target group templates: %s' % ', '.join(
+                    (str(context.style.node(v)) for v in 
self.target_group_template_names)))
+
+
+class GroupPolicyTemplateBase(structure.ModelMixin):
+    """
+    Policies applied to groups.
+
+    Properties:
+
+    * :code:`name`: Name
+    * :code:`description`: Description
+    * :code:`type_name`: Must be represented in the :class:`ModelingContext`
+    * :code:`properties`: Dict of :class:`Parameter`
+    * :code:`triggers`: Dict of :class:`GroupPolicyTrigger`
+    """
+
+    __tablename__ = 'group_policy_template'
+    # region foreign keys
+    @declared_attr
+    def group_template_fk(cls):
+        return cls.foreign_key('group_template')
+
+    # endregion
+
+    description = Column(Text)
+    type_name = Column(Text)
+
+    # region many-to-many relationships
+
+    @declared_attr
+    def properties(cls):
+        return cls.many_to_many_relationship('parameter', 
table_prefix='properties')
+
+    # endregion
+
+    @property
+    def as_raw(self):
+        return collections.OrderedDict((
+            ('name', self.name),
+            ('description', self.description),
+            ('type_name', self.type_name),
+            ('properties', formatting.as_raw_dict(self.properties)),
+            ('triggers', formatting.as_raw_list(self.triggers))))
+
+    def instantiate(self, context, container):
+        group_policy = instance_elements.GroupPolicyBase(self.name, 
self.type_name)
+        group_policy.description = deepcopy_with_locators(self.description)
+        utils.instantiate_dict(context, container, group_policy.properties, 
self.properties)
+        utils.instantiate_dict(context, container, group_policy.triggers, 
self.triggers)
+        return group_policy
+
+    def validate(self, context):
+        if context.modeling.policy_types.get_descendant(self.type_name) is 
None:
+            context.validation.report('group policy "%s" has an unknown type: 
%s'
+                                      % (self.name, 
formatting.safe_repr(self.type_name)),
+                                      level=validation.Issue.BETWEEN_TYPES)
+
+        utils.validate_dict_values(context, self.properties)
+        utils.validate_dict_values(context, self.triggers)
+
+    def coerce_values(self, context, container, report_issues):
+        utils.coerce_dict_values(context, container, self.properties, 
report_issues)
+        utils.coerce_dict_values(context, container, self.triggers, 
report_issues)
+
+    def dump(self, context):
+        console.puts(context.style.node(self.name))
+        if self.description:
+            console.puts(context.style.meta(self.description))
+        with context.style.indent:
+            console.puts('Group policy type: %s' % 
context.style.type(self.type_name))
+            dump_parameters(context, self.properties)
+            utils.dump_dict_values(context, self.triggers, 'Triggers')
+
+
+class GroupPolicyTriggerTemplateBase(structure.ModelMixin):
+    """
+    Triggers for :class:`GroupPolicyTemplate`.
+
+    Properties:
+
+    * :code:`name`: Name
+    * :code:`description`: Description
+    * :code:`implementation`: Implementation string (interpreted by the 
orchestrator)
+    * :code:`properties`: Dict of :class:`Parameter`
+    """
+    __tablename__ = 'group_policy_trigger_template'
+    # region foreign keys
+    @declared_attr
+    def group_policy_template_fk(cls):
+        return cls.foreign_key('group_policy_template')
+
+    # endregion
+
+    description = Column(Text)
+    implementation = Column(Text)
+
+    # region many-to-one relationship
+    @declared_attr
+    def group_policy_template(cls):
+        return cls.many_to_one_relationship('group_policy_template')
+
+    # endregion
+
+
+    # region many-to-many relationships
+
+    @declared_attr
+    def properties(cls):
+        return cls.many_to_many_relationship('parameter', 
table_prefix='properties')
+
+    # endregion
+
+    @property
+    def as_raw(self):
+        return collections.OrderedDict((
+            ('name', self.name),
+            ('description', self.description),
+            ('implementation', self.implementation),
+            ('properties', formatting.as_raw_dict(self.properties))))
+
+    def instantiate(self, context, container):
+        group_policy_trigger = 
instance_elements.GroupPolicyTriggerBase(self.name,
+                                                                        
self.implementation)
+        group_policy_trigger.description = 
deepcopy_with_locators(self.description)
+        utils.instantiate_dict(context, container, 
group_policy_trigger.properties,
+                               self.properties)
+        return group_policy_trigger
+
+    def validate(self, context):
+        utils.validate_dict_values(context, self.properties)
+
+    def coerce_values(self, context, container, report_issues):
+        utils.coerce_dict_values(context, container, self.properties, 
report_issues)
+
+    def dump(self, context):
+        console.puts(context.style.node(self.name))
+        if self.description:
+            console.puts(context.style.meta(self.description))
+        with context.style.indent:
+            console.puts('Implementation: %s' % 
context.style.literal(self.implementation))
+            dump_parameters(context, self.properties)
+
+
+class MappingTemplateBase(structure.ModelMixin):
+    """
+    Used by :class:`SubstitutionTemplate` to map a capability or a requirement 
to a node.
+
+    Properties:
+
+    * :code:`mapped_name`: Exposed capability or requirement name
+    * :code:`node_template_name`: Must be represented in the 
:class:`ServiceModel`
+    * :code:`name`: Name of capability or requirement at the node template
+    """
+    __tablename__ = 'mapping_template'
+
+    mapped_name = Column(Text)
+    node_template_name = Column(Text)
+
+    @property
+    def as_raw(self):
+        return collections.OrderedDict((
+            ('mapped_name', self.mapped_name),
+            ('node_template_name', self.node_template_name),
+            ('name', self.name)))
+
+    def instantiate(self, context, *args, **kwargs):
+        nodes = context.modeling.instance.find_nodes(self.node_template_name)
+        if len(nodes) == 0:
+            context.validation.report(
+                'mapping "%s" refer to node template "%s" but there are no '
+                'node instances' % (self.mapped_name,
+                                    self.node_template_name),
+                level=validation.Issue.BETWEEN_INSTANCES)
+            return None
+        return instance_elements.MappingBase(self.mapped_name, nodes[0].id, 
self.name)
+
+    def validate(self, context):
+        if self.node_template_name not in 
context.modeling.model.node_templates:
+            context.validation.report('mapping "%s" refers to an unknown node 
template: %s'
+                                      % (
+                                          self.mapped_name,
+                                          
formatting.safe_repr(self.node_template_name)),
+                                      level=validation.Issue.BETWEEN_TYPES)
+
+    def dump(self, context):
+        console.puts('%s -> %s.%s' % (context.style.node(self.mapped_name),
+                                      
context.style.node(self.node_template_name),
+                                      context.style.node(self.name)))
+
+
+class SubstitutionTemplateBase(structure.ModelMixin):
+    """
+    Used to substitute a single node for the entire deployment.
+
+    Properties:
+
+    * :code:`node_type_name`: Must be represented in the 
:class:`ModelingContext`
+    * :code:`capability_templates`: Dict of :class:`MappingTemplate`
+    * :code:`requirement_templates`: Dict of :class:`MappingTemplate`
+    """
+    __tablename__ = 'substitution_template'
+    node_type_name = Column(Text)
+
+    # region many-to-many relationships
+
+    @declared_attr
+    def capability_templates(cls):
+        return cls.many_to_many_relationship('mapping_template',
+                                             
table_prefix='capability_templates',
+                                             
relationship_kwargs=dict(lazy='dynamic'))
+
+    @declared_attr
+    def requirement_templates(cls):
+        return cls.many_to_many_relationship('mapping_template',
+                                             
table_prefix='requirement_templates',
+                                             
relationship_kwargs=dict(lazy='dynamic'))
+
+    # endregion
+
+    @property
+    def as_raw(self):
+        return collections.OrderedDict((
+            ('node_type_name', self.node_type_name),
+            ('capability_templates', 
formatting.as_raw_list(self.capability_templates)),
+            ('requirement_templates', 
formatting.as_raw_list(self.requirement_templates))))
+
+    def instantiate(self, context, container):
+        substitution = instance_elements.SubstitutionBase(self.node_type_name)
+        utils.instantiate_dict(context, container, substitution.capabilities,
+                               self.capability_templates)
+        utils.instantiate_dict(context, container, substitution.requirements,
+                               self.requirement_templates)
+        return substitution
+
+    def validate(self, context):
+        if context.modeling.node_types.get_descendant(self.node_type_name) is 
None:
+            context.validation.report('substitution template has an unknown 
type: %s'
+                                      % 
formatting.safe_repr(self.node_type_name),
+                                      level=validation.Issue.BETWEEN_TYPES)
+
+        utils.validate_dict_values(context, self.capability_templates)
+        utils.validate_dict_values(context, self.requirement_templates)
+
+    def coerce_values(self, context, container, report_issues):
+        utils.coerce_dict_values(context, self, self.capability_templates, 
report_issues)
+        utils.coerce_dict_values(context, self, self.requirement_templates, 
report_issues)
+
+    def dump(self, context):
+        console.puts('Substitution template:')
+        with context.style.indent:
+            console.puts('Node type: %s' % 
context.style.type(self.node_type_name))
+            utils.dump_dict_values(context, self.capability_templates,
+                                   'Capability template mappings')
+            utils.dump_dict_values(context, self.requirement_templates,
+                                   'Requirement template mappings')
+
+
+# endregion
+
+# region Node templates
+
+class NodeTemplateBase(structure.ModelMixin):
+    __tablename__ = 'node_template'
+
+    # region foreign_keys
+    @declared_attr
+    def service_template_fk(cls):
+        return cls.foreign_key('service_template')
+
+    @declared_attr
+    def host_fk(cls):
+        return cls.foreign_key('node_template', nullable=True)
+
+    # endregion
+
+    description = Column(Text)
+    type_name = Column(Text)
+    default_instances = Column(Integer, default=1)
+    min_instances = Column(Integer, default=0)
+    max_instances = Column(Integer, default=None)
+    target_node_template_constraints = 
Column(aria_type.StrictList(FunctionType))
+
+    # region orchestrator required columns
+
+    plugins = Column(aria_type.List)
+    type_hierarchy = Column(aria_type.List)
+
+    @declared_attr
+    def host(cls):
+        return cls.relationship_to_self('host_fk')
+
+    @declared_attr
+    def service_template_name(cls):
+        return association_proxy('service_template', cls.name_column_name())
+
+    # endregion
+
+    # region many-to-one relationship
+    @declared_attr
+    def service_template(cls):
+        return cls.many_to_one_relationship('service_template')
+
+    # endregion
+
+    # region many-to-many relationships
+
+    @declared_attr
+    def properties(cls):
+        return cls.many_to_many_relationship('parameter', 
table_prefix='properties')
+
+    # endregion
+
+    def is_target_node_valid(self, target_node_template):
+        if self.target_node_template_constraints:
+            for node_type_constraint in self.target_node_template_constraints:
+                if not node_type_constraint(target_node_template, self):
+                    return False
+        return True
+
+    @property
+    def as_raw(self):
+        return collections.OrderedDict((
+            ('name', self.name),
+            ('description', self.description),
+            ('type_name', self.type_name),
+            ('default_instances', self.default_instances),
+            ('min_instances', self.min_instances),
+            ('max_instances', self.max_instances),
+            ('properties', formatting.as_raw_dict(self.properties)),
+            ('interface_templates', 
formatting.as_raw_list(self.interface_templates)),
+            ('artifact_templates', 
formatting.as_raw_list(self.artifact_templates)),
+            ('capability_templates', 
formatting.as_raw_list(self.capability_templates)),
+            ('requirement_templates', 
formatting.as_raw_list(self.requirement_templates))))
+
+    def instantiate(self, context, *args, **kwargs):
+        node = instance_elements.NodeBase(context, self.type_name, self.name)
+        utils.instantiate_dict(context, node, node.properties, self.properties)
+        utils.instantiate_dict(context, node, node.interfaces, 
self.interface_templates)
+        utils.instantiate_dict(context, node, node.artifacts, 
self.artifact_templates)
+        utils.instantiate_dict(context, node, node.capabilities, 
self.capability_templates)
+        return node
+
+    def validate(self, context):
+        if context.modeling.node_types.get_descendant(self.type_name) is None:
+            context.validation.report('node template "%s" has an unknown type: 
%s'
+                                      % (self.name,
+                                         formatting.safe_repr(self.type_name)),
+                                      level=validation.Issue.BETWEEN_TYPES)
+
+        utils.validate_dict_values(context, self.properties)
+        utils.validate_dict_values(context, self.interface_templates)
+        utils.validate_dict_values(context, self.artifact_templates)
+        utils.validate_dict_values(context, self.capability_templates)
+        utils.validate_list_values(context, self.requirement_templates)
+
+    def coerce_values(self, context, container, report_issues):
+        utils.coerce_dict_values(context, self, self.properties, report_issues)
+        utils.coerce_dict_values(context, self, self.interface_templates, 
report_issues)
+        utils.coerce_dict_values(context, self, self.artifact_templates, 
report_issues)
+        utils.coerce_dict_values(context, self, self.capability_templates, 
report_issues)
+        utils.coerce_list_values(context, self, self.requirement_templates, 
report_issues)
+
+    def dump(self, context):
+        console.puts('Node template: %s' % context.style.node(self.name))
+        if self.description:
+            console.puts(context.style.meta(self.description))
+        with context.style.indent:
+            console.puts('Type: %s' % context.style.type(self.type_name))
+            console.puts('Instances: %d (%d%s)'
+                         % (self.default_instances,
+                            self.min_instances,
+                            (' to %d' % self.max_instances
+                             if self.max_instances is not None
+                             else ' or more')))
+            dump_parameters(context, self.properties)
+            utils.dump_interfaces(context, self.interface_templates)
+            utils.dump_dict_values(context, self.artifact_templates, 'Artifact 
tempaltes')
+            utils.dump_dict_values(context, self.capability_templates, 
'Capability templates')
+            utils.dump_list_values(context, self.requirement_templates, 
'Requirement templates')
+
+
+class GroupTemplateBase(structure.ModelMixin):
+    """
+    A template for creating zero or more :class:`Group` instances.
+
+    Groups are logical containers for zero or more nodes that allow applying 
zero or more
+    :class:`GroupPolicy` instances to the nodes together.
+
+    Properties:
+
+    * :code:`name`: Name (will be used as a prefix for group IDs)
+    * :code:`description`: Description
+    * :code:`type_name`: Must be represented in the :class:`ModelingContext`
+    * :code:`properties`: Dict of :class:`Parameter`
+    * :code:`interface_templates`: Dict of :class:`InterfaceTemplate`
+    * :code:`policy_templates`: Dict of :class:`GroupPolicyTemplate`
+    * :code:`member_node_template_names`: Must be represented in the 
:class:`ServiceModel`
+    * :code:`member_group_template_names`: Must be represented in the 
:class:`ServiceModel`
+    """
+    __tablename__ = 'group_template'
+    # region foreign keys
+
+    @declared_attr
+    def service_template_fk(cls):
+        return cls.foreign_key('service_template')
+
+    # endregion
+
+    description = Column(Text)
+    type_name = Column(Text)
+    member_node_template_names = Column(aria_type.StrictList(basestring))
+    member_group_template_names = Column(aria_type.StrictList(basestring))
+
+    # region many-to-one relationship
+    @declared_attr
+    def service_template(cls):
+        return cls.many_to_one_relationship('service_template')
+
+    # endregion
+
+    # region many-to-many relationships
+
+    @declared_attr
+    def properties(cls):
+        return cls.many_to_many_relationship('parameter', 
table_prefix='properties')
+
+    # endregion
+
+    @property
+    def as_raw(self):
+        return collections.OrderedDict((
+            ('name', self.name),
+            ('description', self.description),
+            ('type_name', self.type_name),
+            ('properties', formatting.as_raw_dict(self.properties)),
+            ('interface_templates', 
formatting.as_raw_list(self.interface_templates)),
+            ('policy_templates', 
formatting.as_raw_list(self.policy_templates)),
+            ('member_node_template_names', self.member_node_template_names),
+            ('member_group_template_names', self.member_group_template_names)))
+
+    def instantiate(self, context, *args, **kwargs):
+        group = instance_elements.GroupBase(context, self.type_name, self.name)
+        utils.instantiate_dict(context, self, group.properties, 
self.properties)
+        utils.instantiate_dict(context, self, group.interfaces, 
self.interface_templates)
+        utils.instantiate_dict(context, self, group.policies, 
self.policy_templates)
+        for member_node_template_name in self.member_node_template_names:
+            group.member_node_ids += \
+                
context.modeling.instance.get_node_ids(member_node_template_name)
+        for member_group_template_name in self.member_group_template_names:
+            group.member_group_ids += \
+                
context.modeling.instance.get_group_ids(member_group_template_name)
+        return group
+
+    def validate(self, context):
+        if context.modeling.group_types.get_descendant(self.type_name) is None:
+            context.validation.report('group template "%s" has an unknown 
type: %s'
+                                      % (self.name, 
formatting.safe_repr(self.type_name)),
+                                      level=validation.Issue.BETWEEN_TYPES)
+
+        utils.validate_dict_values(context, self.properties)
+        utils.validate_dict_values(context, self.interface_templates)
+        utils.validate_dict_values(context, self.policy_templates)
+
+    def coerce_values(self, context, container, report_issues):
+        utils.coerce_dict_values(context, self, self.properties, report_issues)
+        utils.coerce_dict_values(context, self, self.interface_templates, 
report_issues)
+        utils.coerce_dict_values(context, self, self.policy_templates, 
report_issues)
+
+    def dump(self, context):
+        console.puts('Group template: %s' % context.style.node(self.name))
+        if self.description:
+            console.puts(context.style.meta(self.description))
+        with context.style.indent:
+            if self.type_name:
+                console.puts('Type: %s' % context.style.type(self.type_name))
+            dump_parameters(context, self.properties)
+            utils.dump_interfaces(context, self.interface_templates)
+            utils.dump_dict_values(context, self.policy_templates, 'Policy 
templates')
+            if self.member_node_template_names:
+                console.puts('Member node templates: %s' % ', '.join(
+                    (str(context.style.node(v)) for v in 
self.member_node_template_names)))
+
+
+# endregion
+
+# region Relationship templates
+
+class RequirementTemplateBase(structure.ModelMixin):
+    """
+    A requirement for a :class:`NodeTemplate`. During instantiation will be 
matched with a
+    capability of another
+    node.
+
+    Requirements may optionally contain a :class:`RelationshipTemplate` that 
will be created between
+    the nodes.
+
+    Properties:
+
+    * :code:`name`: Name
+    * :code:`target_node_type_name`: Must be represented in the 
:class:`ModelingContext`
+    * :code:`target_node_template_name`: Must be represented in the 
:class:`ServiceModel`
+    * :code:`target_node_template_constraints`: List of :class:`FunctionType`
+    * :code:`target_capability_type_name`: Type of capability in target node
+    * :code:`target_capability_name`: Name of capability in target node
+    * :code:`relationship_template`: :class:`RelationshipTemplate`
+    """
+    __tablename__ = 'requirement_template'
+    # region foreign keys
+    @declared_attr
+    def node_template_fk(cls):
+        return cls.foreign_key('node_template', nullable=True)
+
+    # endregion
+
+
+    target_node_type_name = Column(Text)
+    target_node_template_name = Column(Text)
+    target_node_template_constraints = 
Column(aria_type.StrictList(FunctionType))
+    target_capability_type_name = Column(Text)
+    target_capability_name = Column(Text)
+    # CHECK: ???
+    relationship_template = Column(Text)  # optional
+
+    # region many-to-one relationship
+    @declared_attr
+    def node_template(cls):
+        return cls.many_to_one_relationship('node_template')
+    # endregion
+
+    def instantiate(self, context, container):
+        raise NotImplementedError
+
+    def find_target(self, context, source_node_template):
+        # We might already have a specific node template, so we'll just verify 
it
+        if self.target_node_template_name is not None:
+            target_node_template = \
+                
context.modeling.model.node_templates.get(self.target_node_template_name)
+
+            if not 
source_node_template.is_target_node_valid(target_node_template):
+                context.validation.report('requirement "%s" of node template 
"%s" is for node '
+                                          'template "%s" but it does not match 
constraints'
+                                          % (self.name,
+                                             self.target_node_template_name,
+                                             source_node_template.name),
+                                          level=validation.Issue.BETWEEN_TYPES)
+                return None, None
+
+            if self.target_capability_type_name is not None \
+                    or self.target_capability_name is not None:
+                target_node_capability = self.find_target_capability(context,
+                                                                     
source_node_template,
+                                                                     
target_node_template)
+                if target_node_capability is None:
+                    return None, None
+            else:
+                target_node_capability = None
+
+            return target_node_template, target_node_capability
+
+        # Find first node that matches the type
+        elif self.target_node_type_name is not None:
+            for target_node_template in 
context.modeling.model.node_templates.itervalues():
+                if not 
context.modeling.node_types.is_descendant(self.target_node_type_name,
+                                                                 
target_node_template.type_name):
+                    continue
+
+                if not 
source_node_template.is_target_node_valid(target_node_template):
+                    continue
+
+                target_node_capability = self.find_target_capability(context,
+                                                                     
source_node_template,
+                                                                     
target_node_template)
+                if target_node_capability is None:
+                    continue
+
+                return target_node_template, target_node_capability
+
+        return None, None
+
+    def find_target_capability(self, context, source_node_template, 
target_node_template):
+        for capability_template in 
target_node_template.capability_templates.itervalues():
+            if capability_template.satisfies_requirement(context,
+                                                         source_node_template,
+                                                         self,
+                                                         target_node_template):
+                return capability_template
+        return None
+
+    @property
+    def as_raw(self):
+        return collections.OrderedDict((
+            ('name', self.name),
+            ('target_node_type_name', self.target_node_type_name),
+            ('target_node_template_name', self.target_node_template_name),
+            ('target_capability_type_name', self.target_capability_type_name),
+            ('target_capability_name', self.target_capability_name),
+            ('relationship_template', 
formatting.as_raw(self.relationship_template))))
+
+    def validate(self, context):
+        node_types = context.modeling.node_types
+        capability_types = context.modeling.capability_types
+        if self.target_node_type_name \
+                and node_types.get_descendant(self.target_node_type_name) is 
None:
+            context.validation.report('requirement "%s" refers to an unknown 
node type: %s'
+                                      % (self.name,
+                                         
formatting.safe_repr(self.target_node_type_name)),
+                                      level=validation.Issue.BETWEEN_TYPES)
+        if self.target_capability_type_name and \
+                
capability_types.get_descendant(self.target_capability_type_name is None):
+            context.validation.report('requirement "%s" refers to an unknown 
capability type: %s'
+                                      % (self.name,
+                                         
formatting.safe_repr(self.target_capability_type_name)),
+                                      level=validation.Issue.BETWEEN_TYPES)
+        if self.relationship_template:
+            self.relationship_template.validate(context)
+
+    def coerce_values(self, context, container, report_issues):
+        if self.relationship_template is not None:
+            self.relationship_template.coerce_values(context, container, 
report_issues)
+
+    def dump(self, context):
+        if self.name:
+            console.puts(context.style.node(self.name))
+        else:
+            console.puts('Requirement:')
+        with context.style.indent:
+            if self.target_node_type_name is not None:
+                console.puts('Target node type: %s'
+                             % context.style.type(self.target_node_type_name))
+            elif self.target_node_template_name is not None:
+                console.puts('Target node template: %s'
+                             % 
context.style.node(self.target_node_template_name))
+            if self.target_capability_type_name is not None:
+                console.puts('Target capability type: %s'
+                             % 
context.style.type(self.target_capability_type_name))
+            elif self.target_capability_name is not None:
+                console.puts('Target capability name: %s'
+                             % context.style.node(self.target_capability_name))
+            if self.target_node_template_constraints:
+                console.puts('Target node template constraints:')
+                with context.style.indent:
+                    for constraint in self.target_node_template_constraints:
+                        console.puts(context.style.literal(constraint))
+            if self.relationship_template:
+                console.puts('Relationship:')
+                with context.style.indent:
+                    self.relationship_template.dump(context)
+
+
+class CapabilityTemplateBase(structure.ModelMixin):
+    """
+    A capability of a :class:`NodeTemplate`. Nodes expose zero or more 
capabilities that can be
+    matched with :class:`Requirement` instances of other nodes.
+
+    Properties:
+
+    * :code:`name`: Name
+    * :code:`description`: Description
+    * :code:`type_name`: Must be represented in the :class:`ModelingContext`
+    * :code:`min_occurrences`: Minimum number of requirement matches required
+    * :code:`max_occurrences`: Maximum number of requirement matches allowed
+    * :code:`valid_source_node_type_names`: Must be represented in the 
:class:`ModelingContext`
+    * :code:`properties`: Dict of :class:`Parameter`
+    """
+    __tablename__ = 'capability_template'
+    # region foreign keys
+    @declared_attr
+    def node_template_fk(cls):
+        return cls.foreign_key('node_template', nullable=True)
+
+    # endregion
+
+    description = Column(Text)
+    type_name = Column(Text)
+    min_occurrences = Column(Integer, default=None)  # optional
+    max_occurrences = Column(Integer, default=None)  # optional
+    # CHECK: type?
+    valid_source_node_type_names = Column(Text)
+
+    # region many-to-one relationship
+    @declared_attr
+    def node_template(cls):
+        return cls.many_to_one_relationship('node_template')
+    # endregion
+
+    # region many-to-many relationships
+
+    @declared_attr
+    def properties(cls):
+        return cls.many_to_many_relationship('parameter', 
table_prefix='properties')
+
+    # endregion
+
+    def satisfies_requirement(self,
+                              context,
+                              source_node_template,
+                              requirement,
+                              target_node_template):
+        # Do we match the required capability type?
+        capability_types = context.modeling.capability_types
+        if not 
capability_types.is_descendant(requirement.target_capability_type_name,
+                                              self.type_name):
+            return False
+
+        # Are we in valid_source_node_type_names?
+        if self.valid_source_node_type_names:
+            for valid_source_node_type_name in 
self.valid_source_node_type_names:
+                if not 
context.modeling.node_types.is_descendant(valid_source_node_type_name,
+                                                                 
source_node_template.type_name):
+                    return False
+
+        # Apply requirement constraints
+        if requirement.target_node_template_constraints:
+            for node_type_constraint in 
requirement.target_node_template_constraints:
+                if not node_type_constraint(target_node_template, 
source_node_template):
+                    return False
+
+        return True
+
+    @property
+    def as_raw(self):
+        return collections.OrderedDict((
+            ('name', self.name),
+            ('description', self.description),
+            ('type_name', self.type_name),
+            ('min_occurrences', self.min_occurrences),
+            ('max_occurrences', self.max_occurrences),
+            ('valid_source_node_type_names', 
self.valid_source_node_type_names),
+            ('properties', formatting.as_raw_dict(self.properties))))
+
+    def instantiate(self, context, container):
+        capability = instance_elements.CapabilityBase(self.name, 
self.type_name)
+        capability.min_occurrences = self.min_occurrences
+        capability.max_occurrences = self.max_occurrences
+        utils.instantiate_dict(context, container, capability.properties, 
self.properties)
+        return capability
+
+    def validate(self, context):
+        if context.modeling.capability_types.get_descendant(self.type_name) is 
None:
+            context.validation.report('capability "%s" refers to an unknown 
type: %s'
+                                      % (self.name, 
formatting.safe_repr(self.type)),  # pylint: disable=no-member
+                                      #  TODO fix self.type reference
+                                      level=validation.Issue.BETWEEN_TYPES)
+
+        utils.validate_dict_values(context, self.properties)
+
+    def coerce_values(self, context, container, report_issues):
+        utils.coerce_dict_values(context, self, self.properties, report_issues)
+
+    def dump(self, context):
+        console.puts(context.style.node(self.name))
+        if self.description:
+            console.puts(context.style.meta(self.description))
+        with context.style.indent:
+            console.puts('Type: %s' % context.style.type(self.type_name))
+            console.puts(
+                'Occurrences: %d%s'
+                % (self.min_occurrences or 0, (' to %d' % self.max_occurrences)
+                   if self.max_occurrences is not None else ' or more'))
+            if self.valid_source_node_type_names:
+                console.puts('Valid source node types: %s'
+                             % ', '.join((str(context.style.type(v))
+                                          for v in 
self.valid_source_node_type_names)))
+            dump_parameters(context, self.properties)
+
+# endregion
+
+
+def dump_parameters(context, parameters, name='Properties'):
+    if not parameters:
+        return
+    console.puts('%s:' % name)
+    with context.style.indent:
+        for parameter_name, parameter in parameters.items():
+            if parameter.type_name is not None:
+                console.puts('%s = %s (%s)' % 
(context.style.property(parameter_name),
+                                               
context.style.literal(parameter.value),
+                                               
context.style.type(parameter.type_name)))
+            else:
+                console.puts('%s = %s' % 
(context.style.property(parameter_name),
+                                          
context.style.literal(parameter.value)))
+            if parameter.description:
+                console.puts(context.style.meta(parameter.description))
+
+
+# TODO (left for tal): Move following two methods to some place parser specific
+def deepcopy_with_locators(value):
+    """
+    Like :code:`deepcopy`, but also copies over locators.
+    """
+
+    res = deepcopy(value)
+    copy_locators(res, value)
+    return res
+
+
+def copy_locators(target, source):
+    """
+    Copies over :code:`_locator` for all elements, recursively.
+
+    Assumes that target and source have exactly the same list/dict structure.
+    """
+
+    locator = getattr(source, '_locator', None)
+    if locator is not None:
+        try:
+            setattr(target, '_locator', locator)
+        except AttributeError:
+            pass
+
+    if isinstance(target, list) and isinstance(source, list):
+        for i, _ in enumerate(target):
+            copy_locators(target[i], source[i])
+    elif isinstance(target, dict) and isinstance(source, dict):
+        for k, v in target.items():
+            copy_locators(v, source[k])

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