diff --git a/simpleflow/history.py b/simpleflow/history.py
index ccc3dd95d..dfed7c7d3 100644
--- a/simpleflow/history.py
+++ b/simpleflow/history.py
@@ -4,10 +4,9 @@
 class History(object):
     def __init__(self, history):
         self._history = history
-        self._activities = collections.defaultdict(
-            lambda: {'type': 'activity'})
-        self._child_workflows = collections.defaultdict(
-            lambda: {'type': 'child_workflow'})
+        self._activities = collections.OrderedDict()
+        self._child_workflows = collections.OrderedDict()
+        self._tasks = []
 
     @property
     def events(self):
@@ -29,9 +28,11 @@ def get_activity(event):
                 'version': event.activity_type['version'],
                 'state': event.state,
                 'scheduled_id': event.id,
+                'scheduled_timestamp': event.timestamp,
             }
             if event.activity_id not in self._activities:
                 self._activities[event.activity_id] = activity
+                self._tasks.append(activity)
             else:
                 # When the executor retries a task, it schedules it again.
                 # We have to take care of not overriding some values set by the
@@ -40,20 +41,37 @@ def get_activity(event):
                 # corresponds to the last execution.
                 self._activities[event.activity_id].update(activity)
         elif event.state == 'schedule_failed':
-            activity = self._activities[event.activity_id]
-            activity['state'] = event.state
-            activity['cause'] = event.cause
-            activity['activity_type'] = event.activity_type.copy()
+            activity = {
+                'type': 'activity',
+                'state': event.state,
+                'cause': event.cause,
+                'activity_type': event.activity_type.copy(),
+                'schedule_failed_timestamp': event.timestamp,
+            }
+
+            if event.activity_id not in self._activities:
+                self._activities[event.activity_id] = activity
+                self._tasks.append(activity)
+            else:
+                # When the executor retries a task, it schedules it again.
+                # We have to take care of not overriding some values set by the
+                # previous execution of the task such as the number of retries
+                # in ``retry``.  As the state of the event mutates, it
+                # corresponds to the last execution.
+                self._activities[event.activity_id].update(activity)
+
         elif event.state == 'started':
             activity = get_activity(event)
             activity['state'] = event.state
             activity['identity'] = event.identity
             activity['started_id'] = event.id
+            activity['started_timestamp'] = event.timestamp
         elif event.state == 'completed':
             activity = get_activity(event)
             activity['state'] = event.state
             activity['result'] = event.result
             activity['completed_id'] = event.id
+            activity['completed_timestamp'] = event.timestamp
         elif event.state == 'timed_out':
             activity = get_activity(event)
             activity['state'] = event.state
@@ -62,6 +80,7 @@ def get_activity(event):
                 events[activity['scheduled_id'] - 1],
                 '{}_timeout'.format(event.timeout_type.lower()))
             activity['timed_out_id'] = event.id
+            activity['timed_out_timestamp'] = event.timestamp
             if 'retry' not in activity:
                 activity['retry'] = 0
             else:
@@ -71,6 +90,7 @@ def get_activity(event):
             activity['state'] = event.state
             activity['reason'] = event.reason
             activity['details'] = event.details
+            activity['failed_timestamp'] = event.timestamp
             if 'retry' not in activity:
                 activity['retry'] = 0
             else:
@@ -80,6 +100,7 @@ def get_activity(event):
             activity['state'] = event.state
             if hasattr(event, 'details'):
                 activity['details'] = event.details
+            activity['cancelled_timestamp'] = event.timestamp
 
     def parse_child_workflow_event(self, events, event):
         """Aggregate all the attributes of a workflow in a single entry.
@@ -106,18 +127,25 @@ def get_workflow(event):
                 'state': event.state,
                 'initiated_event_id': event.id,
             }
-            self._child_workflows[event.workflow_id] = workflow
+            workflow['initiated_event_timestamp'] = event.timestamp
+            if event.workflow_id not in self._child_workflows:
+                self._child_workflows[event.workflow_id] = workflow
+                self._tasks.append(workflow)
+            else:
+                self._child_workflows[event.workflow_id].update(workflow)
         elif event.state == 'started':
             workflow = get_workflow(event)
             workflow['state'] = event.state
             workflow['run_id'] = event.workflow_execution['runId']
             workflow['workflow_id'] = event.workflow_execution['workflowId']
             workflow['started_id'] = event.id
+            workflow['started_timestamp'] = event.timestamp
         elif event.state == 'completed':
             workflow = get_workflow(event)
             workflow['state'] = event.state
             workflow['result'] = event.result
             workflow['completed_id'] = event.id
+            workflow['completed_timestamp'] = event.timestamp
 
     def parse(self):
         events = self.events