Add abstract class for dialogue policy

dialoguekit/core/dialogue_policy.py

@@ -0,0 +1,44 @@
+"""Abstract interface for dialogue policy.
+
+The dialogue policy generates a dialogue act by the agent based on the current
+dialogue state (last user's utterance and dialogue history). It defines the flow
+of the conversation, i.e., what steps an agent must take at every stage. The
+annotations of the dialogue act represent what the agent must elicit, recommend,
+or inform. The output of the dialogue policy is converted to a natural language
+response by the natural language generator.
+
+For example, the dialogue act with intent ELICIT is generated if the agent does
+not store any user preferences. For the user intent REVEAL, the dialogue policy
+triggers the generation of an item recommendation (dialogue act with intent
+RECOMMEND).
+"""
+
+from abc import ABC, abstractmethod
+from typing import List
+
+from dialoguekit.core.dialogue_act import DialogueAct
+from dialoguekit.core.utterance import Utterance
+
+
+class DialoguePolicy(ABC):
+    def __init__(self) -> None:
+        """Initializes the dialogue policy."""
+
+    @abstractmethod
+    def next_dialogue_act(
+        self, user_utterance: Utterance, dialogue_history: List[Utterance]
+    ) -> DialogueAct:
+        """Returns the next dialogue act given the user utterance and history.
+
+        This method is most likely used in receive_utterance() in the agent to
+        generate the agent's response. Dialogue act prediction is composed of
+        two steps: intent prediction and annotation prediction.
+
+        Args:
+            user_utterance: The last user utterance.
+            dialogue_history: The dialogue history.
+
+        Returns:
+            The next dialogue act.
+        """
+        raise NotImplementedError