diff --git a/taskflow/engines/action_engine/compiler.py b/taskflow/engines/action_engine/compiler.py
index 32cb58c8..41fe5f96 100644
--- a/taskflow/engines/action_engine/compiler.py
+++ b/taskflow/engines/action_engine/compiler.py
@@ -15,53 +15,34 @@
 #    under the License.
 
 import logging
+import threading
 
 from taskflow import exceptions as exc
 from taskflow import flow
 from taskflow import retry
 from taskflow import task
 from taskflow.types import graph as gr
+from taskflow.types import tree as tr
+from taskflow.utils import lock_utils
 from taskflow.utils import misc
 
 LOG = logging.getLogger(__name__)
 
 
 class Compilation(object):
-    """The result of a compilers compile() is this *immutable* object.
+    """The result of a compilers compile() is this *immutable* object."""
 
-    For now it is just a execution graph but in the future it will grow to
-    include more methods & properties that help the various runtime units
-    execute in a more optimal & featureful manner.
-    """
-    def __init__(self, execution_graph):
+    def __init__(self, execution_graph, hierarchy):
         self._execution_graph = execution_graph
+        self._hierarchy = hierarchy
 
     @property
     def execution_graph(self):
         return self._execution_graph
 
-
-class PatternCompiler(object):
-    """Compiles patterns & atoms into a compilation unit.
-
-    NOTE(harlowja): during this pattern translation process any nested flows
-    will be converted into there equivalent subgraphs. This currently implies
-    that contained atoms in those nested flows, post-translation will no longer
-    be associated with there previously containing flow but instead will lose
-    this identity and what will remain is the logical constraints that there
-    contained flow mandated. In the future this may be changed so that this
-    association is not lost via the compilation process (since it can be
-    useful to retain this relationship).
-    """
-    def compile(self, root):
-        graph = _Flattener(root).flatten()
-        if graph.number_of_nodes() == 0:
-            # Try to get a name attribute, otherwise just use the object
-            # string representation directly if that attribute does not exist.
-            name = getattr(root, 'name', root)
-            raise exc.Empty("Root container '%s' (%s) is empty."
-                            % (name, type(root)))
-        return Compilation(graph)
+    @property
+    def hierarchy(self):
+        return self._hierarchy
 
 
 _RETRY_EDGE_DATA = {
@@ -69,14 +50,15 @@ _RETRY_EDGE_DATA = {
 }
 
 
-class _Flattener(object):
-    """Flattens a root item (task/flow) into a execution graph."""
+class PatternCompiler(object):
+    """Compiles a pattern (or task) into a compilation unit."""
 
     def __init__(self, root, freeze=True):
         self._root = root
-        self._graph = None
         self._history = set()
-        self._freeze = bool(freeze)
+        self._freeze = freeze
+        self._lock = threading.Lock()
+        self._compilation = None
 
     def _add_new_edges(self, graph, nodes_from, nodes_to, edge_attrs):
         """Adds new edges from nodes to other nodes in the specified graph.
@@ -93,72 +75,74 @@ class _Flattener(object):
                     # if it's later modified that the same copy isn't modified.
                     graph.add_edge(u, v, attr_dict=edge_attrs.copy())
 
-    def _flatten(self, item):
-        functor = self._find_flattener(item)
-        if not functor:
-            raise TypeError("Unknown type requested to flatten: %s (%s)"
-                            % (item, type(item)))
+    def _flatten(self, item, parent):
+        functor = self._find_flattener(item, parent)
         self._pre_item_flatten(item)
-        graph = functor(item)
-        self._post_item_flatten(item, graph)
-        return graph
+        graph, node = functor(item, parent)
+        self._post_item_flatten(item, graph, node)
+        return graph, node
 
-    def _find_flattener(self, item):
+    def _find_flattener(self, item, parent):
         """Locates the flattening function to use to flatten the given item."""
         if isinstance(item, flow.Flow):
             return self._flatten_flow
         elif isinstance(item, task.BaseTask):
             return self._flatten_task
         elif isinstance(item, retry.Retry):
-            if len(self._history) == 1:
-                raise TypeError("Retry controller: %s (%s) must only be used"
+            if parent is None:
+                raise TypeError("Retry controller '%s' (%s) must only be used"
                                 " as a flow constructor parameter and not as a"
                                 " root component" % (item, type(item)))
             else:
-                # TODO(harlowja): we should raise this type error earlier
-                # instead of later since we should do this same check on add()
-                # calls, this makes the error more visible (instead of waiting
-                # until compile time).
-                raise TypeError("Retry controller: %s (%s) must only be used"
+                raise TypeError("Retry controller '%s' (%s) must only be used"
                                 " as a flow constructor parameter and not as a"
                                 " flow added component" % (item, type(item)))
         else:
-            return None
+            raise TypeError("Unknown item '%s' (%s) requested to flatten"
+                            % (item, type(item)))
 
     def _connect_retry(self, retry, graph):
         graph.add_node(retry)
 
-        # All graph nodes that have no predecessors should depend on its retry
-        nodes_to = [n for n in graph.no_predecessors_iter() if n != retry]
+        # All nodes that have no predecessors should depend on this retry.
+        nodes_to = [n for n in graph.no_predecessors_iter() if n is not retry]
         self._add_new_edges(graph, [retry], nodes_to, _RETRY_EDGE_DATA)
 
-        # Add link to retry for each node of subgraph that hasn't
-        # a parent retry
+        # Add association for each node of graph that has no existing retry.
         for n in graph.nodes_iter():
-            if n != retry and 'retry' not in graph.node[n]:
+            if n is not retry and 'retry' not in graph.node[n]:
                 graph.node[n]['retry'] = retry
 
-    def _flatten_task(self, task):
+    def _flatten_task(self, task, parent):
         """Flattens a individual task."""
         graph = gr.DiGraph(name=task.name)
         graph.add_node(task)
-        return graph
+        node = tr.Node(task)
+        if parent is not None:
+            parent.add(node)
+        return graph, node
 
-    def _flatten_flow(self, flow):
-        """Flattens a graph flow."""
+    def _flatten_flow(self, flow, parent):
+        """Flattens a flow."""
         graph = gr.DiGraph(name=flow.name)
+        node = tr.Node(flow)
+        if parent is not None:
+            parent.add(node)
+        if flow.retry is not None:
+            node.add(tr.Node(flow.retry))
 
-        # Flatten all nodes into a single subgraph per node.
-        subgraph_map = {}
+        # Flatten all nodes into a single subgraph per item (and track origin
+        # item to its newly expanded graph).
+        subgraphs = {}
         for item in flow:
-            subgraph = self._flatten(item)
-            subgraph_map[item] = subgraph
+            subgraph = self._flatten(item, node)[0]
+            subgraphs[item] = subgraph
             graph = gr.merge_graphs([graph, subgraph])
 
-        # Reconnect all node edges to their corresponding subgraphs.
+        # Reconnect all items edges to their corresponding subgraphs.
         for (u, v, attrs) in flow.iter_links():
-            u_g = subgraph_map[u]
-            v_g = subgraph_map[v]
+            u_g = subgraphs[u]
+            v_g = subgraphs[v]
             if any(attrs.get(k) for k in ('invariant', 'manual', 'retry')):
                 # Connect nodes with no predecessors in v to nodes with
                 # no successors in u (thus maintaining the edge dependency).
@@ -177,48 +161,57 @@ class _Flattener(object):
 
         if flow.retry is not None:
             self._connect_retry(flow.retry, graph)
-        return graph
+        return graph, node
 
     def _pre_item_flatten(self, item):
         """Called before a item is flattened; any pre-flattening actions."""
-        if id(item) in self._history:
-            raise ValueError("Already flattened item: %s (%s), recursive"
-                             " flattening not supported" % (item, id(item)))
-        self._history.add(id(item))
+        if item in self._history:
+            raise ValueError("Already flattened item '%s' (%s), recursive"
+                             " flattening is not supported" % (item,
+                                                               type(item)))
+        self._history.add(item)
 
-    def _post_item_flatten(self, item, graph):
-        """Called before a item is flattened; any post-flattening actions."""
+    def _post_item_flatten(self, item, graph, node):
+        """Called after a item is flattened; doing post-flattening actions."""
 
     def _pre_flatten(self):
-        """Called before the flattening of the item starts."""
+        """Called before the flattening of the root starts."""
         self._history.clear()
 
-    def _post_flatten(self, graph):
-        """Called after the flattening of the item finishes successfully."""
+    def _post_flatten(self, graph, node):
+        """Called after the flattening of the root finishes successfully."""
         dup_names = misc.get_duplicate_keys(graph.nodes_iter(),
                                             key=lambda node: node.name)
         if dup_names:
-            dup_names = ', '.join(sorted(dup_names))
-            raise exc.Duplicate("Atoms with duplicate names "
-                                "found: %s" % (dup_names))
+            raise exc.Duplicate(
+                "Atoms with duplicate names found: %s" % (sorted(dup_names)))
+        if graph.number_of_nodes() == 0:
+            raise exc.Empty("Root container '%s' (%s) is empty"
+                            % (self._root, type(self._root)))
         self._history.clear()
         # NOTE(harlowja): this one can be expensive to calculate (especially
         # the cycle detection), so only do it if we know debugging is enabled
         # and not under all cases.
         if LOG.isEnabledFor(logging.DEBUG):
-            LOG.debug("Translated '%s' into a graph:", self._root)
+            LOG.debug("Translated '%s'", self._root)
+            LOG.debug("Graph:")
             for line in graph.pformat().splitlines():
                 # Indent it so that it's slightly offset from the above line.
-                LOG.debug(" %s", line)
+                LOG.debug("  %s", line)
+            LOG.debug("Hierarchy:")
+            for line in node.pformat().splitlines():
+                # Indent it so that it's slightly offset from the above line.
+                LOG.debug("  %s", line)
 
-    def flatten(self):
-        """Flattens a item (a task or flow) into a single execution graph."""
-        if self._graph is not None:
-            return self._graph
-        self._pre_flatten()
-        graph = self._flatten(self._root)
-        self._post_flatten(graph)
-        self._graph = graph
-        if self._freeze:
-            self._graph.freeze()
-        return self._graph
+    @lock_utils.locked
+    def compile(self):
+        """Compiles the contained item into a compiled equivalent."""
+        if self._compilation is None:
+            self._pre_flatten()
+            graph, node = self._flatten(self._root, None)
+            self._post_flatten(graph, node)
+            if self._freeze:
+                graph.freeze()
+                node.freeze()
+            self._compilation = Compilation(graph, node)
+        return self._compilation
diff --git a/taskflow/engines/action_engine/engine.py b/taskflow/engines/action_engine/engine.py
index 9bf62429..3aaa3226 100644
--- a/taskflow/engines/action_engine/engine.py
+++ b/taskflow/engines/action_engine/engine.py
@@ -211,13 +211,13 @@ class ActionEngine(base.EngineBase):
 
     @misc.cachedproperty
     def _compiler(self):
-        return self._compiler_factory()
+        return self._compiler_factory(self._flow)
 
     @lock_utils.locked
     def compile(self):
         if self._compiled:
             return
-        self._compilation = self._compiler.compile(self._flow)
+        self._compilation = self._compiler.compile()
         self._runtime = runtime.Runtime(self._compilation,
                                         self.storage,
                                         self.task_notifier,
diff --git a/taskflow/engines/action_engine/retry_action.py b/taskflow/engines/action_engine/retry_action.py
index afdfb456..e4df5afa 100644
--- a/taskflow/engines/action_engine/retry_action.py
+++ b/taskflow/engines/action_engine/retry_action.py
@@ -27,13 +27,16 @@ SAVE_RESULT_STATES = (states.SUCCESS, states.FAILURE)
 
 
 class RetryAction(object):
-    def __init__(self, storage, notifier):
+    def __init__(self, storage, notifier, walker_factory):
         self._storage = storage
         self._notifier = notifier
+        self._walker_factory = walker_factory
 
     def _get_retry_args(self, retry):
+        scope_walker = self._walker_factory(retry)
         kwargs = self._storage.fetch_mapped_args(retry.rebind,
-                                                 atom_name=retry.name)
+                                                 atom_name=retry.name,
+                                                 scope_walker=scope_walker)
         kwargs['history'] = self._storage.get_retry_history(retry.name)
         return kwargs
 
diff --git a/taskflow/engines/action_engine/runtime.py b/taskflow/engines/action_engine/runtime.py
index 90913b99..c0c58367 100644
--- a/taskflow/engines/action_engine/runtime.py
+++ b/taskflow/engines/action_engine/runtime.py
@@ -18,6 +18,7 @@ from taskflow.engines.action_engine import analyzer as ca
 from taskflow.engines.action_engine import executor as ex
 from taskflow.engines.action_engine import retry_action as ra
 from taskflow.engines.action_engine import runner as ru
+from taskflow.engines.action_engine import scopes as sc
 from taskflow.engines.action_engine import task_action as ta
 from taskflow import exceptions as excp
 from taskflow import retry as retry_atom
@@ -66,12 +67,18 @@ class Runtime(object):
 
     @misc.cachedproperty
     def retry_action(self):
-        return ra.RetryAction(self.storage, self._task_notifier)
+        return ra.RetryAction(self._storage, self._task_notifier,
+                              lambda atom: sc.ScopeWalker(self.compilation,
+                                                          atom,
+                                                          names_only=True))
 
     @misc.cachedproperty
     def task_action(self):
-        return ta.TaskAction(self.storage, self._task_executor,
-                             self._task_notifier)
+        return ta.TaskAction(self._storage, self._task_executor,
+                             self._task_notifier,
+                             lambda atom: sc.ScopeWalker(self.compilation,
+                                                         atom,
+                                                         names_only=True))
 
     def reset_nodes(self, nodes, state=st.PENDING, intention=st.EXECUTE):
         for node in nodes:
@@ -81,7 +88,7 @@ class Runtime(object):
                 elif isinstance(node, retry_atom.Retry):
                     self.retry_action.change_state(node, state)
                 else:
-                    raise TypeError("Unknown how to reset node %s, %s"
+                    raise TypeError("Unknown how to reset atom '%s' (%s)"
                                     % (node, type(node)))
             if intention:
                 self.storage.set_atom_intention(node.name, intention)
@@ -209,7 +216,7 @@ class Scheduler(object):
         elif isinstance(node, retry_atom.Retry):
             return self._schedule_retry(node)
         else:
-            raise TypeError("Unknown how to schedule node %s, %s"
+            raise TypeError("Unknown how to schedule atom '%s' (%s)"
                             % (node, type(node)))
 
     def _schedule_retry(self, retry):
diff --git a/taskflow/engines/action_engine/scopes.py b/taskflow/engines/action_engine/scopes.py
new file mode 100644
index 00000000..f1dd49d1
--- /dev/null
+++ b/taskflow/engines/action_engine/scopes.py
@@ -0,0 +1,119 @@
+# -*- coding: utf-8 -*-
+
+#    Copyright (C) 2014 Yahoo! Inc. All Rights Reserved.
+#
+#    Licensed 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.
+
+import logging
+
+from taskflow import atom as atom_type
+from taskflow import flow as flow_type
+
+LOG = logging.getLogger(__name__)
+
+
+def _extract_atoms(node, idx=-1):
+    # Always go left to right, since right to left is the pattern order
+    # and we want to go backwards and not forwards through that ordering...
+    if idx == -1:
+        children_iter = node.reverse_iter()
+    else:
+        children_iter = reversed(node[0:idx])
+    atoms = []
+    for child in children_iter:
+        if isinstance(child.item, flow_type.Flow):
+            atoms.extend(_extract_atoms(child))
+        elif isinstance(child.item, atom_type.Atom):
+            atoms.append(child.item)
+        else:
+            raise TypeError(
+                "Unknown extraction item '%s' (%s)" % (child.item,
+                                                       type(child.item)))
+    return atoms
+
+
+class ScopeWalker(object):
+    """Walks through the scopes of a atom using a engines compilation.
+
+    This will walk the visible scopes that are accessible for the given
+    atom, which can be used by some external entity in some meaningful way,
+    for example to find dependent values...
+    """
+
+    def __init__(self, compilation, atom, names_only=False):
+        self._node = compilation.hierarchy.find(atom)
+        if self._node is None:
+            raise ValueError("Unable to find atom '%s' in compilation"
+                             " hierarchy" % atom)
+        self._atom = atom
+        self._graph = compilation.execution_graph
+        self._names_only = names_only
+
+    def __iter__(self):
+        """Iterates over the visible scopes.
+
+        How this works is the following:
+
+        We find all the possible predecessors of the given atom, this is useful
+        since we know they occurred before this atom but it doesn't tell us
+        the corresponding scope *level* that each predecessor was created in,
+        so we need to find this information.
+
+        For that information we consult the location of the atom ``Y`` in the
+        node hierarchy. We lookup in a reverse order the parent ``X`` of ``Y``
+        and traverse backwards from the index in the parent where ``Y``
+        occurred, all children in ``X`` that we encounter in this backwards
+        search (if a child is a flow itself, its atom contents will be
+        expanded) will be assumed to be at the same scope. This is then a
+        *potential* single scope, to make an *actual* scope we remove the items
+        from the *potential* scope that are not predecessors of ``Y`` to form
+        the *actual* scope.
+
+        Then for additional scopes we continue up the tree, by finding the
+        parent of ``X`` (lets call it ``Z``) and perform the same operation,
+        going through the children in a reverse manner from the index in
+        parent ``Z`` where ``X`` was located. This forms another *potential*
+        scope which we provide back as an *actual* scope after reducing the
+        potential set by the predecessors of ``Y``. We then repeat this process
+        until we no longer have any parent nodes (aka have reached the top of
+        the tree) or we run out of predecessors.
+        """
+        predecessors = set(self._graph.bfs_predecessors_iter(self._atom))
+        last = self._node
+        for parent in self._node.path_iter(include_self=False):
+            if not predecessors:
+                break
+            last_idx = parent.index(last.item)
+            visible = []
+            for a in _extract_atoms(parent, idx=last_idx):
+                if a in predecessors:
+                    predecessors.remove(a)
+                    if not self._names_only:
+                        visible.append(a)
+                    else:
+                        visible.append(a.name)
+            if LOG.isEnabledFor(logging.DEBUG):
+                if not self._names_only:
+                    visible_names = [a.name for a in visible]
+                else:
+                    visible_names = visible
+                # TODO(harlowja): we should likely use a created TRACE level
+                # for this kind of *very* verbose information; otherwise the
+                # cinder and other folks are going to complain that there
+                # debug logs are full of not so useful information (it is
+                # useful to taskflow debugging...).
+                LOG.debug("Scope visible to '%s' (limited by parent '%s' index"
+                          " < %s) is: %s", self._atom, parent.item.name,
+                          last_idx, visible_names)
+            yield visible
+            last = parent
diff --git a/taskflow/engines/action_engine/task_action.py b/taskflow/engines/action_engine/task_action.py
index a07ded79..3503df7c 100644
--- a/taskflow/engines/action_engine/task_action.py
+++ b/taskflow/engines/action_engine/task_action.py
@@ -26,10 +26,11 @@ SAVE_RESULT_STATES = (states.SUCCESS, states.FAILURE)
 
 class TaskAction(object):
 
-    def __init__(self, storage, task_executor, notifier):
+    def __init__(self, storage, task_executor, notifier, walker_factory):
         self._storage = storage
         self._task_executor = task_executor
         self._notifier = notifier
+        self._walker_factory = walker_factory
 
     def _is_identity_transition(self, state, task, progress):
         if state in SAVE_RESULT_STATES:
@@ -81,8 +82,10 @@ class TaskAction(object):
 
     def schedule_execution(self, task):
         self.change_state(task, states.RUNNING, progress=0.0)
+        scope_walker = self._walker_factory(task)
         kwargs = self._storage.fetch_mapped_args(task.rebind,
-                                                 atom_name=task.name)
+                                                 atom_name=task.name,
+                                                 scope_walker=scope_walker)
         task_uuid = self._storage.get_atom_uuid(task.name)
         return self._task_executor.execute_task(task, task_uuid, kwargs,
                                                 self._on_update_progress)
@@ -96,8 +99,10 @@ class TaskAction(object):
 
     def schedule_reversion(self, task):
         self.change_state(task, states.REVERTING, progress=0.0)
+        scope_walker = self._walker_factory(task)
         kwargs = self._storage.fetch_mapped_args(task.rebind,
-                                                 atom_name=task.name)
+                                                 atom_name=task.name,
+                                                 scope_walker=scope_walker)
         task_uuid = self._storage.get_atom_uuid(task.name)
         task_result = self._storage.get(task.name)
         failures = self._storage.get_failures()
diff --git a/taskflow/patterns/graph_flow.py b/taskflow/patterns/graph_flow.py
index 9717b211..658e051c 100644
--- a/taskflow/patterns/graph_flow.py
+++ b/taskflow/patterns/graph_flow.py
@@ -161,7 +161,7 @@ class Flow(flow.Flow):
         return self._get_subgraph().number_of_nodes()
 
     def __iter__(self):
-        for n in self._get_subgraph().nodes_iter():
+        for n in self._get_subgraph().topological_sort():
             yield n
 
     def iter_links(self):
diff --git a/taskflow/storage.py b/taskflow/storage.py
index 31a8868f..bcc2b157 100644
--- a/taskflow/storage.py
+++ b/taskflow/storage.py
@@ -31,6 +31,78 @@ from taskflow.utils import reflection
 LOG = logging.getLogger(__name__)
 STATES_WITH_RESULTS = (states.SUCCESS, states.REVERTING, states.FAILURE)
 
+# TODO(harlowja): do this better (via a singleton or something else...)
+_TRANSIENT_PROVIDER = object()
+
+# NOTE(harlowja): Perhaps the container is a dictionary-like object and that
+# key does not exist (key error), or the container is a tuple/list and a
+# non-numeric key is being requested (index error), or there was no container
+# and an attempt to index into none/other unsubscriptable type is being
+# requested (type error).
+#
+# Overall this (along with the item_from* functions) try to handle the vast
+# majority of wrong indexing operations on the wrong/invalid types so that we
+# can fail extraction during lookup or emit warning on result reception...
+_EXTRACTION_EXCEPTIONS = (IndexError, KeyError, ValueError, TypeError)
+
+
+class _Provider(object):
+    """A named symbol provider that produces a output at the given index."""
+
+    def __init__(self, name, index):
+        self.name = name
+        self.index = index
+
+    def __repr__(self):
+        # TODO(harlowja): clean this up...
+        if self.name is _TRANSIENT_PROVIDER:
+            base = "<TransientProvider"
+        else:
+            base = "<Provider '%s'" % (self.name)
+        if self.index is None:
+            base += ">"
+        else:
+            base += " @ index %r>" % (self.index)
+        return base
+
+    def __hash__(self):
+        return hash((self.name, self.index))
+
+    def __eq__(self, other):
+        return (self.name, self.index) == (other.name, other.index)
+
+
+def _item_from(container, index):
+    """Attempts to fetch a index/key from a given container."""
+    if index is None:
+        return container
+    return container[index]
+
+
+def _item_from_single(provider, container, looking_for):
+    """Returns item from a *single* provider."""
+    try:
+        return _item_from(container, provider.index)
+    except _EXTRACTION_EXCEPTIONS:
+        raise exceptions.NotFound(
+            "Unable to find result %r, expected to be able to find it"
+            " created by %s but was unable to perform successful"
+            " extraction" % (looking_for, provider))
+
+
+def _item_from_first_of(providers, looking_for):
+    """Returns item from the *first* successful container extraction."""
+    for (provider, container) in providers:
+        try:
+            return (provider, _item_from(container, provider.index))
+        except _EXTRACTION_EXCEPTIONS:
+            pass
+    providers = [p[0] for p in providers]
+    raise exceptions.NotFound(
+        "Unable to find result %r, expected to be able to find it"
+        " created by one of %s but was unable to perform successful"
+        " extraction" % (looking_for, providers))
+
 
 @six.add_metaclass(abc.ABCMeta)
 class Storage(object):
@@ -313,7 +385,7 @@ class Storage(object):
             except KeyError:
                 return None
 
-    def _check_all_results_provided(self, atom_name, data):
+    def _check_all_results_provided(self, atom_name, container):
         """Warn if an atom did not provide some of its expected results.
 
         This may happen if atom returns shorter tuple or list or dict
@@ -325,8 +397,8 @@ class Storage(object):
             return
         for name, index in six.iteritems(result_mapping):
             try:
-                misc.item_from(data, index, name=name)
-            except exceptions.NotFound:
+                _item_from(container, index)
+            except _EXTRACTION_EXCEPTIONS:
                 LOG.warning("Atom %s did not supply result "
                             "with index %r (name %s)", atom_name, index, name)
 
@@ -464,94 +536,180 @@ class Storage(object):
 
         def save_transient():
             self._transients.update(pairs)
-            # NOTE(harlowja): none is not a valid atom name, so that means
-            # we can use it internally to reference all of our transient
-            # variables.
-            return (None, six.iterkeys(self._transients))
+            return (_TRANSIENT_PROVIDER, six.iterkeys(self._transients))
 
         with self._lock.write_lock():
             if transient:
-                (atom_name, names) = save_transient()
+                provider_name, names = save_transient()
             else:
-                (atom_name, names) = save_persistent()
-            self._set_result_mapping(atom_name,
+                provider_name, names = save_persistent()
+            self._set_result_mapping(provider_name,
                                      dict((name, name) for name in names))
 
-    def _set_result_mapping(self, atom_name, mapping):
-        """Sets the result mapping for an atom.
+    def _set_result_mapping(self, provider_name, mapping):
+        """Sets the result mapping for a given producer.
 
         The result saved with given name would be accessible by names
         defined in mapping. Mapping is a dict name => index. If index
         is None, the whole result will have this name; else, only
         part of it, result[index].
         """
-        if not mapping:
-            return
-        self._result_mappings[atom_name] = mapping
-        for name, index in six.iteritems(mapping):
-            entries = self._reverse_mapping.setdefault(name, [])
+        provider_mapping = self._result_mappings.setdefault(provider_name, {})
+        if mapping:
+            provider_mapping.update(mapping)
+            # Ensure the reverse mapping/index is updated (for faster lookups).
+            for name, index in six.iteritems(provider_mapping):
+                entries = self._reverse_mapping.setdefault(name, [])
+                provider = _Provider(provider_name, index)
+                if provider not in entries:
+                    entries.append(provider)
 
-            # NOTE(imelnikov): We support setting same result mapping for
-            # the same atom twice (e.g when we are injecting 'a' and then
-            # injecting 'a' again), so we should not log warning below in
-            # that case and we should have only one item for each pair
-            # (atom_name, index) in entries. It should be put to the end of
-            # entries list because order matters on fetching.
-            try:
-                entries.remove((atom_name, index))
-            except ValueError:
-                pass
-
-            entries.append((atom_name, index))
-            if len(entries) > 1:
-                LOG.warning("Multiple provider mappings being created for %r",
-                            name)
-
-    def fetch(self, name):
-        """Fetch a named atoms result."""
+    def fetch(self, name, many_handler=None):
+        """Fetch a named result."""
+        # By default we just return the first of many (unless provided
+        # a different callback that can translate many results into something
+        # more meaningful).
+        if many_handler is None:
+            many_handler = lambda values: values[0]
         with self._lock.read_lock():
             try:
-                indexes = self._reverse_mapping[name]
+                providers = self._reverse_mapping[name]
             except KeyError:
-                raise exceptions.NotFound("Name %r is not mapped" % name)
-            # Return the first one that is found.
-            for (atom_name, index) in reversed(indexes):
-                if not atom_name:
-                    results = self._transients
+                raise exceptions.NotFound("Name %r is not mapped as a"
+                                          " produced output by any"
+                                          " providers" % name)
+            values = []
+            for provider in providers:
+                if provider.name is _TRANSIENT_PROVIDER:
+                    values.append(_item_from_single(provider,
+                                                    self._transients, name))
                 else:
-                    results = self._get(atom_name, only_last=True)
-                try:
-                    return misc.item_from(results, index, name)
-                except exceptions.NotFound:
-                    pass
-            raise exceptions.NotFound("Unable to find result %r" % name)
+                    try:
+                        container = self._get(provider.name, only_last=True)
+                    except exceptions.NotFound:
+                        pass
+                    else:
+                        values.append(_item_from_single(provider,
+                                                        container, name))
+            if not values:
+                raise exceptions.NotFound("Unable to find result %r,"
+                                          " searched %s" % (name, providers))
+            else:
+                return many_handler(values)
 
     def fetch_all(self):
-        """Fetch all named atom results known so far.
+        """Fetch all named results known so far.
 
-        Should be used for debugging and testing purposes mostly.
+        NOTE(harlowja): should be used for debugging and testing purposes.
         """
+        def many_handler(values):
+            if len(values) > 1:
+                return values
+            return values[0]
         with self._lock.read_lock():
             results = {}
-            for name in self._reverse_mapping:
+            for name in six.iterkeys(self._reverse_mapping):
                 try:
-                    results[name] = self.fetch(name)
+                    results[name] = self.fetch(name, many_handler=many_handler)
                 except exceptions.NotFound:
                     pass
             return results
 
-    def fetch_mapped_args(self, args_mapping, atom_name=None):
-        """Fetch arguments for an atom using an atoms arguments mapping."""
+    def fetch_mapped_args(self, args_mapping,
+                          atom_name=None, scope_walker=None):
+        """Fetch arguments for an atom using an atoms argument mapping."""
+
+        def _get_results(looking_for, provider):
+            """Gets the results saved for a given provider."""
+            try:
+                return self._get(provider.name, only_last=True)
+            except exceptions.NotFound as e:
+                raise exceptions.NotFound(
+                    "Expected to be able to find output %r produced"
+                    " by %s but was unable to get at that providers"
+                    " results" % (looking_for, provider), e)
+
+        def _locate_providers(looking_for, possible_providers):
+            """Finds the accessible providers."""
+            default_providers = []
+            for p in possible_providers:
+                if p.name is _TRANSIENT_PROVIDER:
+                    default_providers.append((p, self._transients))
+                if p.name == self.injector_name:
+                    default_providers.append((p, _get_results(looking_for, p)))
+            if default_providers:
+                return default_providers
+            if scope_walker is not None:
+                scope_iter = iter(scope_walker)
+            else:
+                scope_iter = iter([])
+            for atom_names in scope_iter:
+                if not atom_names:
+                    continue
+                providers = []
+                for p in possible_providers:
+                    if p.name in atom_names:
+                        providers.append((p, _get_results(looking_for, p)))
+                if providers:
+                    return providers
+            return []
+
         with self._lock.read_lock():
-            injected_args = {}
+            if atom_name and atom_name not in self._atom_name_to_uuid:
+                raise exceptions.NotFound("Unknown atom name: %s" % atom_name)
+            if not args_mapping:
+                return {}
+            # The order of lookup is the following:
+            #
+            # 1. Injected atom specific arguments.
+            # 2. Transient injected arguments.
+            # 3. Non-transient injected arguments.
+            # 4. First scope visited group that produces the named result.
+            #    a). The first of that group that actually provided the name
+            #        result is selected (if group size is greater than one).
+            #
+            # Otherwise: blowup! (this will also happen if reading or
+            # extracting an expected result fails, since it is better to fail
+            # on lookup then provide invalid data from the wrong provider)
             if atom_name:
                 injected_args = self._injected_args.get(atom_name, {})
+            else:
+                injected_args = {}
             mapped_args = {}
-            for key, name in six.iteritems(args_mapping):
+            for (bound_name, name) in six.iteritems(args_mapping):
+                # TODO(harlowja): This logging information may be to verbose
+                # even for DEBUG mode, let's see if we can maybe in the future
+                # add a TRACE mode or something else if people complain...
+                if LOG.isEnabledFor(logging.DEBUG):
+                    if atom_name:
+                        LOG.debug("Looking for %r <= %r for atom named: %s",
+                                  bound_name, name, atom_name)
+                    else:
+                        LOG.debug("Looking for %r <= %r", bound_name, name)
                 if name in injected_args:
-                    mapped_args[key] = injected_args[name]
+                    value = injected_args[name]
+                    mapped_args[bound_name] = value
+                    LOG.debug("Matched %r <= %r to %r (from injected values)",
+                              bound_name, name, value)
                 else:
-                    mapped_args[key] = self.fetch(name)
+                    try:
+                        possible_providers = self._reverse_mapping[name]
+                    except KeyError:
+                        raise exceptions.NotFound("Name %r is not mapped as a"
+                                                  " produced output by any"
+                                                  " providers" % name)
+                    # Reduce the possible providers to one that are allowed.
+                    providers = _locate_providers(name, possible_providers)
+                    if not providers:
+                        raise exceptions.NotFound(
+                            "Mapped argument %r <= %r was not produced"
+                            " by any accessible provider (%s possible"
+                            " providers were scanned)"
+                            % (bound_name, name, len(possible_providers)))
+                    provider, value = _item_from_first_of(providers, name)
+                    mapped_args[bound_name] = value
+                    LOG.debug("Matched %r <= %r to %r (from %s)",
+                              bound_name, name, value, provider)
             return mapped_args
 
     def set_flow_state(self, state):
diff --git a/taskflow/tests/unit/action_engine/test_compile.py b/taskflow/tests/unit/action_engine/test_compile.py
index 7207468e..63b3c0b0 100644
--- a/taskflow/tests/unit/action_engine/test_compile.py
+++ b/taskflow/tests/unit/action_engine/test_compile.py
@@ -27,21 +27,25 @@ from taskflow.tests import utils as test_utils
 class PatternCompileTest(test.TestCase):
     def test_task(self):
         task = test_utils.DummyTask(name='a')
-        compilation = compiler.PatternCompiler().compile(task)
+        compilation = compiler.PatternCompiler(task).compile()
         g = compilation.execution_graph
         self.assertEqual(list(g.nodes()), [task])
         self.assertEqual(list(g.edges()), [])
 
     def test_retry(self):
         r = retry.AlwaysRevert('r1')
-        msg_regex = "^Retry controller: .* must only be used .*"
+        msg_regex = "^Retry controller .* must only be used .*"
         self.assertRaisesRegexp(TypeError, msg_regex,
-                                compiler.PatternCompiler().compile, r)
+                                compiler.PatternCompiler(r).compile)
 
     def test_wrong_object(self):
-        msg_regex = '^Unknown type requested to flatten'
+        msg_regex = '^Unknown item .* requested to flatten'
         self.assertRaisesRegexp(TypeError, msg_regex,
-                                compiler.PatternCompiler().compile, 42)
+                                compiler.PatternCompiler(42).compile)
+
+    def test_empty(self):
+        flo = lf.Flow("test")
+        self.assertRaises(exc.Empty, compiler.PatternCompiler(flo).compile)
 
     def test_linear(self):
         a, b, c, d = test_utils.make_many(4)
@@ -51,7 +55,7 @@ class PatternCompileTest(test.TestCase):
         sflo.add(d)
         flo.add(sflo)
 
-        compilation = compiler.PatternCompiler().compile(flo)
+        compilation = compiler.PatternCompiler(flo).compile()
         g = compilation.execution_graph
         self.assertEqual(4, len(g))
 
@@ -69,13 +73,13 @@ class PatternCompileTest(test.TestCase):
         flo.add(a, b, c)
         flo.add(flo)
         self.assertRaises(ValueError,
-                          compiler.PatternCompiler().compile, flo)
+                          compiler.PatternCompiler(flo).compile)
 
     def test_unordered(self):
         a, b, c, d = test_utils.make_many(4)
         flo = uf.Flow("test")
         flo.add(a, b, c, d)
-        compilation = compiler.PatternCompiler().compile(flo)
+        compilation = compiler.PatternCompiler(flo).compile()
         g = compilation.execution_graph
         self.assertEqual(4, len(g))
         self.assertEqual(0, g.number_of_edges())
@@ -92,7 +96,7 @@ class PatternCompileTest(test.TestCase):
         flo2.add(c, d)
         flo.add(flo2)
 
-        compilation = compiler.PatternCompiler().compile(flo)
+        compilation = compiler.PatternCompiler(flo).compile()
         g = compilation.execution_graph
         self.assertEqual(4, len(g))
 
@@ -116,7 +120,7 @@ class PatternCompileTest(test.TestCase):
         flo2.add(c, d)
         flo.add(flo2)
 
-        compilation = compiler.PatternCompiler().compile(flo)
+        compilation = compiler.PatternCompiler(flo).compile()
         g = compilation.execution_graph
         self.assertEqual(4, len(g))
         for n in [a, b]:
@@ -138,7 +142,7 @@ class PatternCompileTest(test.TestCase):
             uf.Flow('ut').add(b, c),
             d)
 
-        compilation = compiler.PatternCompiler().compile(flo)
+        compilation = compiler.PatternCompiler(flo).compile()
         g = compilation.execution_graph
         self.assertEqual(4, len(g))
         self.assertItemsEqual(g.edges(), [
@@ -153,7 +157,7 @@ class PatternCompileTest(test.TestCase):
         flo = gf.Flow("test")
         flo.add(a, b, c, d)
 
-        compilation = compiler.PatternCompiler().compile(flo)
+        compilation = compiler.PatternCompiler(flo).compile()
         g = compilation.execution_graph
         self.assertEqual(4, len(g))
         self.assertEqual(0, g.number_of_edges())
@@ -167,7 +171,7 @@ class PatternCompileTest(test.TestCase):
         flo2.add(e, f, g)
         flo.add(flo2)
 
-        compilation = compiler.PatternCompiler().compile(flo)
+        compilation = compiler.PatternCompiler(flo).compile()
         graph = compilation.execution_graph
         self.assertEqual(7, len(graph))
         self.assertItemsEqual(graph.edges(data=True), [
@@ -184,7 +188,7 @@ class PatternCompileTest(test.TestCase):
         flo2.add(e, f, g)
         flo.add(flo2)
 
-        compilation = compiler.PatternCompiler().compile(flo)
+        compilation = compiler.PatternCompiler(flo).compile()
         g = compilation.execution_graph
         self.assertEqual(7, len(g))
         self.assertEqual(0, g.number_of_edges())
@@ -197,7 +201,7 @@ class PatternCompileTest(test.TestCase):
         flo.link(b, c)
         flo.link(c, d)
 
-        compilation = compiler.PatternCompiler().compile(flo)
+        compilation = compiler.PatternCompiler(flo).compile()
         g = compilation.execution_graph
         self.assertEqual(4, len(g))
         self.assertItemsEqual(g.edges(data=True), [
@@ -213,7 +217,7 @@ class PatternCompileTest(test.TestCase):
         b = test_utils.ProvidesRequiresTask('b', provides=[], requires=['x'])
         flo = gf.Flow("test").add(a, b)
 
-        compilation = compiler.PatternCompiler().compile(flo)
+        compilation = compiler.PatternCompiler(flo).compile()
         g = compilation.execution_graph
         self.assertEqual(2, len(g))
         self.assertItemsEqual(g.edges(data=True), [
@@ -231,7 +235,7 @@ class PatternCompileTest(test.TestCase):
             lf.Flow("test2").add(b, c)
         )
 
-        compilation = compiler.PatternCompiler().compile(flo)
+        compilation = compiler.PatternCompiler(flo).compile()
         g = compilation.execution_graph
         self.assertEqual(3, len(g))
         self.assertItemsEqual(g.edges(data=True), [
@@ -250,7 +254,7 @@ class PatternCompileTest(test.TestCase):
             lf.Flow("test2").add(b, c)
         )
 
-        compilation = compiler.PatternCompiler().compile(flo)
+        compilation = compiler.PatternCompiler(flo).compile()
         g = compilation.execution_graph
         self.assertEqual(3, len(g))
         self.assertItemsEqual(g.edges(data=True), [
@@ -267,7 +271,7 @@ class PatternCompileTest(test.TestCase):
         )
         self.assertRaisesRegexp(exc.Duplicate,
                                 '^Atoms with duplicate names',
-                                compiler.PatternCompiler().compile, flo)
+                                compiler.PatternCompiler(flo).compile)
 
     def test_checks_for_dups_globally(self):
         flo = gf.Flow("test").add(
@@ -275,25 +279,25 @@ class PatternCompileTest(test.TestCase):
             gf.Flow("int2").add(test_utils.DummyTask(name="a")))
         self.assertRaisesRegexp(exc.Duplicate,
                                 '^Atoms with duplicate names',
-                                compiler.PatternCompiler().compile, flo)
+                                compiler.PatternCompiler(flo).compile)
 
     def test_retry_in_linear_flow(self):
         flo = lf.Flow("test", retry.AlwaysRevert("c"))
-        compilation = compiler.PatternCompiler().compile(flo)
+        compilation = compiler.PatternCompiler(flo).compile()
         g = compilation.execution_graph
         self.assertEqual(1, len(g))
         self.assertEqual(0, g.number_of_edges())
 
     def test_retry_in_unordered_flow(self):
         flo = uf.Flow("test", retry.AlwaysRevert("c"))
-        compilation = compiler.PatternCompiler().compile(flo)
+        compilation = compiler.PatternCompiler(flo).compile()
         g = compilation.execution_graph
         self.assertEqual(1, len(g))
         self.assertEqual(0, g.number_of_edges())
 
     def test_retry_in_graph_flow(self):
         flo = gf.Flow("test", retry.AlwaysRevert("c"))
-        compilation = compiler.PatternCompiler().compile(flo)
+        compilation = compiler.PatternCompiler(flo).compile()
         g = compilation.execution_graph
         self.assertEqual(1, len(g))
         self.assertEqual(0, g.number_of_edges())
@@ -302,7 +306,7 @@ class PatternCompileTest(test.TestCase):
         c1 = retry.AlwaysRevert("c1")
         c2 = retry.AlwaysRevert("c2")
         flo = lf.Flow("test", c1).add(lf.Flow("test2", c2))
-        compilation = compiler.PatternCompiler().compile(flo)
+        compilation = compiler.PatternCompiler(flo).compile()
         g = compilation.execution_graph
 
         self.assertEqual(2, len(g))
@@ -317,7 +321,7 @@ class PatternCompileTest(test.TestCase):
         c = retry.AlwaysRevert("c")
         a, b = test_utils.make_many(2)
         flo = lf.Flow("test", c).add(a, b)
-        compilation = compiler.PatternCompiler().compile(flo)
+        compilation = compiler.PatternCompiler(flo).compile()
         g = compilation.execution_graph
 
         self.assertEqual(3, len(g))
@@ -335,7 +339,7 @@ class PatternCompileTest(test.TestCase):
         c = retry.AlwaysRevert("c")
         a, b = test_utils.make_many(2)
         flo = uf.Flow("test", c).add(a, b)
-        compilation = compiler.PatternCompiler().compile(flo)
+        compilation = compiler.PatternCompiler(flo).compile()
         g = compilation.execution_graph
 
         self.assertEqual(3, len(g))
@@ -353,7 +357,7 @@ class PatternCompileTest(test.TestCase):
         r = retry.AlwaysRevert("cp")
         a, b, c = test_utils.make_many(3)
         flo = gf.Flow("test", r).add(a, b, c).link(b, c)
-        compilation = compiler.PatternCompiler().compile(flo)
+        compilation = compiler.PatternCompiler(flo).compile()
         g = compilation.execution_graph
         self.assertEqual(4, len(g))
 
@@ -377,7 +381,7 @@ class PatternCompileTest(test.TestCase):
             a,
             lf.Flow("test", c2).add(b, c),
             d)
-        compilation = compiler.PatternCompiler().compile(flo)
+        compilation = compiler.PatternCompiler(flo).compile()
         g = compilation.execution_graph
 
         self.assertEqual(6, len(g))
@@ -402,7 +406,7 @@ class PatternCompileTest(test.TestCase):
             a,
             lf.Flow("test").add(b, c),
             d)
-        compilation = compiler.PatternCompiler().compile(flo)
+        compilation = compiler.PatternCompiler(flo).compile()
         g = compilation.execution_graph
 
         self.assertEqual(5, len(g))
diff --git a/taskflow/tests/unit/action_engine/test_runner.py b/taskflow/tests/unit/action_engine/test_runner.py
index 2e18f6b6..82440fc5 100644
--- a/taskflow/tests/unit/action_engine/test_runner.py
+++ b/taskflow/tests/unit/action_engine/test_runner.py
@@ -33,7 +33,7 @@ from taskflow.utils import persistence_utils as pu
 
 class _RunnerTestMixin(object):
     def _make_runtime(self, flow, initial_state=None):
-        compilation = compiler.PatternCompiler().compile(flow)
+        compilation = compiler.PatternCompiler(flow).compile()
         flow_detail = pu.create_flow_detail(flow)
         store = storage.SingleThreadedStorage(flow_detail)
         # This ensures the tasks exist in storage...
diff --git a/taskflow/tests/unit/test_action_engine_scoping.py b/taskflow/tests/unit/test_action_engine_scoping.py
new file mode 100644
index 00000000..e2de763f
--- /dev/null
+++ b/taskflow/tests/unit/test_action_engine_scoping.py
@@ -0,0 +1,248 @@
+# -*- coding: utf-8 -*-
+
+#    Copyright (C) 2014 Yahoo! Inc. All Rights Reserved.
+#
+#    Licensed 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 taskflow.engines.action_engine import compiler
+from taskflow.engines.action_engine import scopes as sc
+from taskflow.patterns import graph_flow as gf
+from taskflow.patterns import linear_flow as lf
+from taskflow.patterns import unordered_flow as uf
+from taskflow import test
+from taskflow.tests import utils as test_utils
+
+
+def _get_scopes(compilation, atom, names_only=True):
+    walker = sc.ScopeWalker(compilation, atom, names_only=names_only)
+    return list(iter(walker))
+
+
+class LinearScopingTest(test.TestCase):
+    def test_unknown(self):
+        r = lf.Flow("root")
+        r_1 = test_utils.TaskOneReturn("root.1")
+        r.add(r_1)
+
+        r_2 = test_utils.TaskOneReturn("root.2")
+        c = compiler.PatternCompiler(r).compile()
+        self.assertRaises(ValueError, _get_scopes, c, r_2)
+
+    def test_empty(self):
+        r = lf.Flow("root")
+        r_1 = test_utils.TaskOneReturn("root.1")
+        r.add(r_1)
+
+        c = compiler.PatternCompiler(r).compile()
+        self.assertIn(r_1, c.execution_graph)
+        self.assertIsNotNone(c.hierarchy.find(r_1))
+
+        walker = sc.ScopeWalker(c, r_1)
+        scopes = list(walker)
+        self.assertEqual([], scopes)
+
+    def test_single_prior_linear(self):
+        r = lf.Flow("root")
+        r_1 = test_utils.TaskOneReturn("root.1")
+        r_2 = test_utils.TaskOneReturn("root.2")
+        r.add(r_1, r_2)
+
+        c = compiler.PatternCompiler(r).compile()
+        for a in r:
+            self.assertIn(a, c.execution_graph)
+            self.assertIsNotNone(c.hierarchy.find(a))
+
+        self.assertEqual([], _get_scopes(c, r_1))
+        self.assertEqual([['root.1']], _get_scopes(c, r_2))
+
+    def test_nested_prior_linear(self):
+        r = lf.Flow("root")
+        r.add(test_utils.TaskOneReturn("root.1"),
+              test_utils.TaskOneReturn("root.2"))
+        sub_r = lf.Flow("subroot")
+        sub_r_1 = test_utils.TaskOneReturn("subroot.1")
+        sub_r.add(sub_r_1)
+        r.add(sub_r)
+
+        c = compiler.PatternCompiler(r).compile()
+        self.assertEqual([[], ['root.2', 'root.1']], _get_scopes(c, sub_r_1))
+
+    def test_nested_prior_linear_begin_middle_end(self):
+        r = lf.Flow("root")
+        begin_r = test_utils.TaskOneReturn("root.1")
+        r.add(begin_r, test_utils.TaskOneReturn("root.2"))
+        middle_r = test_utils.TaskOneReturn("root.3")
+        r.add(middle_r)
+        sub_r = lf.Flow("subroot")
+        sub_r.add(test_utils.TaskOneReturn("subroot.1"),
+                  test_utils.TaskOneReturn("subroot.2"))
+        r.add(sub_r)
+        end_r = test_utils.TaskOneReturn("root.4")
+        r.add(end_r)
+
+        c = compiler.PatternCompiler(r).compile()
+
+        self.assertEqual([], _get_scopes(c, begin_r))
+        self.assertEqual([['root.2', 'root.1']], _get_scopes(c, middle_r))
+        self.assertEqual([['subroot.2', 'subroot.1', 'root.3', 'root.2',
+                           'root.1']], _get_scopes(c, end_r))
+
+
+class GraphScopingTest(test.TestCase):
+    def test_dependent(self):
+        r = gf.Flow("root")
+
+        customer = test_utils.ProvidesRequiresTask("customer",
+                                                   provides=['dog'],
+                                                   requires=[])
+        washer = test_utils.ProvidesRequiresTask("washer",
+                                                 requires=['dog'],
+                                                 provides=['wash'])
+        dryer = test_utils.ProvidesRequiresTask("dryer",
+                                                requires=['dog', 'wash'],
+                                                provides=['dry_dog'])
+        shaved = test_utils.ProvidesRequiresTask("shaver",
+                                                 requires=['dry_dog'],
+                                                 provides=['shaved_dog'])
+        happy_customer = test_utils.ProvidesRequiresTask(
+            "happy_customer", requires=['shaved_dog'], provides=['happiness'])
+
+        r.add(customer, washer, dryer, shaved, happy_customer)
+
+        c = compiler.PatternCompiler(r).compile()
+
+        self.assertEqual([], _get_scopes(c, customer))
+        self.assertEqual([['washer', 'customer']], _get_scopes(c, dryer))
+        self.assertEqual([['shaver', 'dryer', 'washer', 'customer']],
+                         _get_scopes(c, happy_customer))
+
+    def test_no_visible(self):
+        r = gf.Flow("root")
+        atoms = []
+        for i in range(0, 10):
+            atoms.append(test_utils.TaskOneReturn("root.%s" % i))
+        r.add(*atoms)
+
+        c = compiler.PatternCompiler(r).compile()
+        for a in atoms:
+            self.assertEqual([], _get_scopes(c, a))
+
+    def test_nested(self):
+        r = gf.Flow("root")
+
+        r_1 = test_utils.TaskOneReturn("root.1")
+        r_2 = test_utils.TaskOneReturn("root.2")
+        r.add(r_1, r_2)
+        r.link(r_1, r_2)
+
+        subroot = gf.Flow("subroot")
+        subroot_r_1 = test_utils.TaskOneReturn("subroot.1")
+        subroot_r_2 = test_utils.TaskOneReturn("subroot.2")
+        subroot.add(subroot_r_1, subroot_r_2)
+        subroot.link(subroot_r_1, subroot_r_2)
+
+        r.add(subroot)
+        r_3 = test_utils.TaskOneReturn("root.3")
+        r.add(r_3)
+        r.link(r_2, r_3)
+
+        c = compiler.PatternCompiler(r).compile()
+        self.assertEqual([], _get_scopes(c, r_1))
+        self.assertEqual([['root.1']], _get_scopes(c, r_2))
+        self.assertEqual([['root.2', 'root.1']], _get_scopes(c, r_3))
+
+        self.assertEqual([], _get_scopes(c, subroot_r_1))
+        self.assertEqual([['subroot.1']], _get_scopes(c, subroot_r_2))
+
+
+class UnorderedScopingTest(test.TestCase):
+    def test_no_visible(self):
+        r = uf.Flow("root")
+        atoms = []
+        for i in range(0, 10):
+            atoms.append(test_utils.TaskOneReturn("root.%s" % i))
+        r.add(*atoms)
+        c = compiler.PatternCompiler(r).compile()
+        for a in atoms:
+            self.assertEqual([], _get_scopes(c, a))
+
+
+class MixedPatternScopingTest(test.TestCase):
+    def test_graph_linear_scope(self):
+        r = gf.Flow("root")
+        r_1 = test_utils.TaskOneReturn("root.1")
+        r_2 = test_utils.TaskOneReturn("root.2")
+        r.add(r_1, r_2)
+        r.link(r_1, r_2)
+
+        s = lf.Flow("subroot")
+        s_1 = test_utils.TaskOneReturn("subroot.1")
+        s_2 = test_utils.TaskOneReturn("subroot.2")
+        s.add(s_1, s_2)
+        r.add(s)
+
+        t = gf.Flow("subroot2")
+        t_1 = test_utils.TaskOneReturn("subroot2.1")
+        t_2 = test_utils.TaskOneReturn("subroot2.2")
+        t.add(t_1, t_2)
+        t.link(t_1, t_2)
+        r.add(t)
+        r.link(s, t)
+
+        c = compiler.PatternCompiler(r).compile()
+        self.assertEqual([], _get_scopes(c, r_1))
+        self.assertEqual([['root.1']], _get_scopes(c, r_2))
+        self.assertEqual([], _get_scopes(c, s_1))
+        self.assertEqual([['subroot.1']], _get_scopes(c, s_2))
+        self.assertEqual([[], ['subroot.2', 'subroot.1']],
+                         _get_scopes(c, t_1))
+        self.assertEqual([["subroot2.1"], ['subroot.2', 'subroot.1']],
+                         _get_scopes(c, t_2))
+
+    def test_linear_unordered_scope(self):
+        r = lf.Flow("root")
+        r_1 = test_utils.TaskOneReturn("root.1")
+        r_2 = test_utils.TaskOneReturn("root.2")
+        r.add(r_1, r_2)
+
+        u = uf.Flow("subroot")
+        atoms = []
+        for i in range(0, 5):
+            atoms.append(test_utils.TaskOneReturn("subroot.%s" % i))
+        u.add(*atoms)
+        r.add(u)
+
+        r_3 = test_utils.TaskOneReturn("root.3")
+        r.add(r_3)
+
+        c = compiler.PatternCompiler(r).compile()
+
+        self.assertEqual([], _get_scopes(c, r_1))
+        self.assertEqual([['root.1']], _get_scopes(c, r_2))
+        for a in atoms:
+            self.assertEqual([[], ['root.2', 'root.1']], _get_scopes(c, a))
+
+        scope = _get_scopes(c, r_3)
+        self.assertEqual(1, len(scope))
+        first_root = 0
+        for i, n in enumerate(scope[0]):
+            if n.startswith('root.'):
+                first_root = i
+                break
+        first_subroot = 0
+        for i, n in enumerate(scope[0]):
+            if n.startswith('subroot.'):
+                first_subroot = i
+                break
+        self.assertGreater(first_subroot, first_root)
+        self.assertEqual(scope[0][-2:], ['root.2', 'root.1'])
diff --git a/taskflow/tests/unit/test_storage.py b/taskflow/tests/unit/test_storage.py
index 94d73012..3c74bebe 100644
--- a/taskflow/tests/unit/test_storage.py
+++ b/taskflow/tests/unit/test_storage.py
@@ -453,23 +453,6 @@ class StorageTestMixin(object):
         self.assertRaisesRegexp(exceptions.NotFound,
                                 '^Unable to find result', s.fetch, 'b')
 
-    @mock.patch.object(storage.LOG, 'warning')
-    def test_multiple_providers_are_checked(self, mocked_warning):
-        s = self._get_storage()
-        s.ensure_task('my task', result_mapping={'result': 'key'})
-        self.assertEqual(mocked_warning.mock_calls, [])
-        s.ensure_task('my other task', result_mapping={'result': 'key'})
-        mocked_warning.assert_called_once_with(
-            mock.ANY, 'result')
-
-    @mock.patch.object(storage.LOG, 'warning')
-    def test_multiple_providers_with_inject_are_checked(self, mocked_warning):
-        s = self._get_storage()
-        s.inject({'result': 'DONE'})
-        self.assertEqual(mocked_warning.mock_calls, [])
-        s.ensure_task('my other task', result_mapping={'result': 'key'})
-        mocked_warning.assert_called_once_with(mock.ANY, 'result')
-
     def test_ensure_retry(self):
         s = self._get_storage()
         s.ensure_retry('my retry')
diff --git a/taskflow/types/tree.py b/taskflow/types/tree.py
index 759e0fda..1c520966 100644
--- a/taskflow/types/tree.py
+++ b/taskflow/types/tree.py
@@ -167,6 +167,11 @@ class Node(object):
         for c in self._children:
             yield c
 
+    def reverse_iter(self):
+        """Iterates over the direct children of this node (left->right)."""
+        for c in reversed(self._children):
+            yield c
+
     def index(self, item):
         """Finds the child index of a given item, searches in added order."""
         index_at = None
diff --git a/taskflow/utils/misc.py b/taskflow/utils/misc.py
index d05e68db..fd3fc5e7 100644
--- a/taskflow/utils/misc.py
+++ b/taskflow/utils/misc.py
@@ -268,24 +268,6 @@ def sequence_minus(seq1, seq2):
     return result
 
 
-def item_from(container, index, name=None):
-    """Attempts to fetch a index/key from a given container."""
-    if index is None:
-        return container
-    try:
-        return container[index]
-    except (IndexError, KeyError, ValueError, TypeError):
-        # NOTE(harlowja): Perhaps the container is a dictionary-like object
-        # and that key does not exist (key error), or the container is a
-        # tuple/list and a non-numeric key is being requested (index error),
-        # or there was no container and an attempt to index into none/other
-        # unsubscriptable type is being requested (type error).
-        if name is None:
-            name = index
-        raise exc.NotFound("Unable to find %r in container %s"
-                           % (name, container))
-
-
 def get_duplicate_keys(iterable, key=None):
     if key is not None:
         iterable = compat_map(key, iterable)
@@ -410,8 +392,8 @@ def ensure_tree(path):
     """
     try:
         os.makedirs(path)
-    except OSError as exc:
-        if exc.errno == errno.EEXIST:
+    except OSError as e:
+        if e.errno == errno.EEXIST:
             if not os.path.isdir(path):
                 raise
         else: