diff --git a/components/ChatView/MessageTextarea.tsx b/components/ChatView/MessageTextarea.tsx
index 0e22b86..2e082cc 100644
--- a/components/ChatView/MessageTextarea.tsx
+++ b/components/ChatView/MessageTextarea.tsx
@@ -2,6 +2,7 @@ import { useEffect, useRef, useState } from "react";
 import { toast } from "react-hot-toast";
 import TextareaAutosize from "react-textarea-autosize";
 import { localUser, useChatStore, useMessageStore } from "../../store";
+import { CreatorRole } from "../../types";
 import { generateUUID } from "../../utils";
 import Icon from "../Icon";
 
@@ -45,6 +46,7 @@ const MessageTextarea = (props: Props) => {
       id: generateUUID(),
       chatId: chatStore.currentChat.id,
       creatorId: localUser.id,
+      creatorRole: CreatorRole.User,
       createdAt: Date.now(),
       content: value,
     });
diff --git a/components/ChatView/index.tsx b/components/ChatView/index.tsx
index 72aafd3..cd9d0d7 100644
--- a/components/ChatView/index.tsx
+++ b/components/ChatView/index.tsx
@@ -1,7 +1,7 @@
 import axios from "axios";
 import { useEffect, useRef, useState } from "react";
 import { defaultChat, getAssistantById, getPromptOfAssistant, localUser, useChatStore, useMessageStore } from "../../store";
-import { Chat, Message, UserRole } from "../../types";
+import { Chat, CreatorRole, Message } from "../../types";
 import { generateUUID } from "../../utils";
 import Icon from "../Icon";
 import Header from "./Header";
@@ -50,11 +50,11 @@ const ChatView = () => {
     const { data } = await axios.post<string>("/api/chat", {
       messages: [
         {
-          role: "system",
+          role: CreatorRole.System,
           content: prompt,
         },
         ...messageList.map((message) => ({
-          role: message.creatorId === localUser.id ? UserRole.User : UserRole.Assistant,
+          role: message.creatorId === localUser.id ? CreatorRole.User : CreatorRole.Assistant,
           content: message.content,
         })),
       ],
@@ -63,6 +63,7 @@ const ChatView = () => {
       id: generateUUID(),
       chatId: currentChat.id,
       creatorId: currentChat.assistantId,
+      creatorRole: CreatorRole.Assistant,
       createdAt: Date.now(),
       content: data,
     });
diff --git a/store/assistant.ts b/store/assistant.ts
index 9191ece..8fc5827 100644
--- a/store/assistant.ts
+++ b/store/assistant.ts
@@ -1,5 +1,5 @@
 import { first } from "lodash-es";
-import { Id, User, UserRole } from "../types";
+import { Id, User } from "../types";
 
 // Assistant is a special user.
 export const assistantList: User[] = [
@@ -8,7 +8,6 @@ export const assistantList: User[] = [
     name: "SQL Chat",
     description: "🤖️ I'm an expert in SQL. I can answer your questions about databases and SQL.",
     avatar: "",
-    role: UserRole.Assistant,
   },
 ];
 
diff --git a/store/chat.ts b/store/chat.ts
index 0875bd3..c43beff 100644
--- a/store/chat.ts
+++ b/store/chat.ts
@@ -1,10 +1,12 @@
 import { create } from "zustand";
 import { persist } from "zustand/middleware";
-import { Chat, User } from "../types";
+import { Chat, UNKNOWN_ID, User } from "../types";
 import { generateUUID } from "../utils";
 
 export const defaultChat: Chat = {
   id: generateUUID(),
+  connectionId: UNKNOWN_ID,
+  databaseName: "",
   assistantId: "sql-assistant",
 };
 
@@ -20,10 +22,12 @@ export const useChatStore = create<ChatState>()(
     (set) => ({
       chatList: [defaultChat],
       currentChat: defaultChat,
-      createChat: (user: User) => {
+      createChat: (assistant: User) => {
         const chat: Chat = {
           id: generateUUID(),
-          assistantId: user.id,
+          connectionId: UNKNOWN_ID,
+          databaseName: "",
+          assistantId: assistant.id,
         };
         set((state) => ({
           chatList: [...state.chatList, chat],
diff --git a/store/user.ts b/store/user.ts
index d8aa722..fb08010 100644
--- a/store/user.ts
+++ b/store/user.ts
@@ -1,9 +1,8 @@
-import { User, UserRole } from "../types";
+import { User } from "../types";
 
 export const localUser: User = {
   id: "local-user",
   name: "Local user",
   description: "",
   avatar: "",
-  role: UserRole.User,
 };
diff --git a/types/chat.ts b/types/chat.ts
index 05d8581..1822194 100644
--- a/types/chat.ts
+++ b/types/chat.ts
@@ -2,5 +2,7 @@ import { Id } from "./common";
 
 export interface Chat {
   id: string;
+  connectionId: Id;
+  databaseName: string;
   assistantId: Id;
 }
diff --git a/types/common.ts b/types/common.ts
index e5bada3..2049883 100644
--- a/types/common.ts
+++ b/types/common.ts
@@ -1,2 +1,4 @@
 export type Id = string;
 export type Timestamp = number;
+
+export const UNKNOWN_ID = "unknown";
diff --git a/types/connection.ts b/types/connection.ts
new file mode 100644
index 0000000..e5c4480
--- /dev/null
+++ b/types/connection.ts
@@ -0,0 +1,18 @@
+import { Id } from "./common";
+
+enum Engine {
+  MySQL = "MYSQL",
+  PostgreSQL = "POSTGRESQL",
+}
+
+export interface Connection {
+  id: Id;
+  title: string;
+  engineType: Engine;
+  host: string;
+  port: string;
+  username: string;
+  password: string;
+  // database is only required for PostgreSQL.
+  database?: string;
+}
diff --git a/types/database.ts b/types/database.ts
new file mode 100644
index 0000000..277b2a6
--- /dev/null
+++ b/types/database.ts
@@ -0,0 +1,14 @@
+import { Id } from "./common";
+
+export interface Database {
+  connectionId: Id;
+  name: string;
+  tableList: Table[];
+}
+
+interface Table {
+  name: string;
+  // structure is a string of the table structure.
+  // It's mainly used for providing a chat context for the assistant.
+  structure: string;
+}
diff --git a/types/message.ts b/types/message.ts
index 1cfe635..3860f59 100644
--- a/types/message.ts
+++ b/types/message.ts
@@ -1,9 +1,16 @@
 import { Id, Timestamp } from "./";
 
+export enum CreatorRole {
+  System = "system",
+  User = "user",
+  Assistant = "assistant",
+}
+
 export interface Message {
   id: Id;
   chatId: string;
   creatorId: Id;
+  creatorRole: CreatorRole;
   createdAt: Timestamp;
   content: string;
 }
diff --git a/types/user.ts b/types/user.ts
index 85b3a35..224dd1e 100644
--- a/types/user.ts
+++ b/types/user.ts
@@ -1,13 +1,6 @@
-export enum UserRole {
-  System = "system",
-  User = "user",
-  Assistant = "assistant",
-}
-
 export interface User {
   id: string;
   name: string;
   description: string;
   avatar: string;
-  role: UserRole;
 }