diff --git a/app/models.py b/app/models.py
index 3d20425..364ac3f 100644
--- a/app/models.py
+++ b/app/models.py
@@ -66,3 +66,36 @@ class AuditTrail(Base):
     action = Column(String)
     details = Column(Text)
     timestamp = Column(DateTime, default=datetime.utcnow)
+
+# ***
+
+# All comments are in English.
+
+from sqlalchemy import Column, String, Text, DateTime, ForeignKey
+from sqlalchemy.orm import declarative_base, relationship
+from datetime import datetime
+
+Base = declarative_base()
+
+class Conversation(Base):
+    __tablename__ = "conversations"
+    id = Column(String, primary_key=True)
+    title = Column(String)
+    messages = relationship("Message", back_populates="conversation")
+
+class Message(Base):
+    __tablename__ = "messages"
+    id = Column(String, primary_key=True)
+    conversation_id = Column(String, ForeignKey("conversations.id"))
+    role = Column(String)  # "user" or "assistant"
+    content = Column(Text)
+    created_at = Column(DateTime, default=datetime.utcnow)
+    conversation = relationship("Conversation", back_populates="messages")
+
+class Attachment(Base):
+    __tablename__ = "attachments"
+    id = Column(String, primary_key=True)
+    conversation_id = Column(String, ForeignKey("conversations.id"))
+    filename = Column(String)
+    mime_type = Column(String)
+    data = Column(Text)  # base64 or small text payload