add DST backbone

dst.py

@@ -0,0 +1,34 @@
+class SimpleRuleDST:
+    def __init__(self):
+        self.state = None
+        self.init_session()
+
+    def update(self, user_act=None):
+        for intent, domain, slot, value in user_act:
+            domain = domain.lower()
+            intent = intent.lower()
+            slot = slot.lower()
+            value = slot.lower()
+
+            if domain not in self.state['belief_state']:
+                continue
+
+            if intent == 'inform':
+                if slot == 'none' or slot == '':
+                    continue
+
+                domain_dic = self.state['belief_state'][domain]
+
+                if slot in domain_dic:
+                    self.state['belief_state'][domain][slot] = value
+
+            elif intent == 'request':
+                if domain not in self.state['request_state']:
+                    self.state['request_state'][domain] = {}
+                if slot not in self.state['request_state'][domain]:
+                    self.state['request_state'][domain][slot] = 0
+
+        return self.state
+
+    def init_session(self):
+        self.state = None