diff --git a/lib/db/data_provider.dart b/lib/db/data_provider.dart
new file mode 100644
index 0000000..7a30880
--- /dev/null
+++ b/lib/db/data_provider.dart
@@ -0,0 +1,44 @@
+import 'package:flutter/material.dart';
+import 'package:timemanage/model/project.dart';
+import 'package:timemanage/model/timer_entry.dart';
+
+abstract class DataProvider {
+  Future<Project> createProject({required String name, Color? colour});
+  Future<List<Project>> listProjects();
+  Future<void> editProject(Project project);
+  Future<void> deleteProject(Project project);
+  Future<TimerEntry> createTimer({
+    String? description,
+    int? projectID,
+    DateTime? startTime,
+    DateTime? endTime,
+  });
+  Future<List<TimerEntry>> listTimers();
+  Future<void> editTimer(TimerEntry timer);
+  Future<void> deleteTimer(TimerEntry timer);
+
+  Future<void> import(DataProvider other) async {
+    List<TimerEntry> otherEntries = await other.listTimers();
+    List<Project> otherProjects = await other.listProjects();
+
+    List<Project> newOtherProjects = await Stream.fromIterable(otherProjects)
+        .asyncMap((event) => createProject(name: event.name))
+        .toList();
+
+    for (TimerEntry otherEntry in otherEntries) {
+      int projectOffset = otherProjects
+          .indexWhere((element) => element.id == otherEntry.projectID);
+      int? projectID;
+      if (projectOffset >= 0) {
+        projectID = newOtherProjects[projectOffset].id;
+      }
+
+      await createTimer(
+        description: otherEntry.description,
+        projectID: projectID,
+        startTime: otherEntry.startTime,
+        endTime: otherEntry.endTime,
+      );
+    }
+  }
+}
diff --git a/lib/db/database_provider.dart b/lib/db/database_provider.dart
new file mode 100644
index 0000000..238c774
--- /dev/null
+++ b/lib/db/database_provider.dart
@@ -0,0 +1,259 @@
+import 'dart:async';
+import 'dart:io';
+import 'package:flutter/material.dart';
+import 'package:sqflite/sqflite.dart';
+import 'package:timemanage/db/data_provider.dart';
+import 'package:timemanage/model/timer_entry.dart';
+import 'package:timemanage/model/project.dart';
+import 'package:path/path.dart' as p;
+import 'package:xdg_directories/xdg_directories.dart';
+
+class DatabaseProvider extends DataProvider {
+  final Database _db;
+  static const int _dbVersion = 4;
+
+  DatabaseProvider(this._db);
+
+  Future<void> close() async {
+    await _db.close();
+  }
+
+  static void _onConfigure(Database db) async {
+    await db.execute("PRAGMA foreign_keys = OFF");
+  }
+
+  static void _onCreate(Database db, int version) async {
+    await db.execute('''
+      create table if not exists projects(
+        id integer not null primary key autoincrement,
+        name text not null,
+        colour int not null,
+        archived boolean not null default 0
+      )
+    ''');
+    await db.execute('''
+      create table if not exists timers(
+        id integer not null primary key autoincrement,
+        project_id integer default null,
+        description text not null,
+        start_time int not null,
+        end_time int default null,
+        notes text default null,
+        foreign key(project_id) references projects(id) on delete set null
+      )
+    ''');
+    await db.execute('''
+      create index if not exists timers_start_time on timers(start_time)
+    ''');
+  }
+
+  static void _onUpgrade(Database db, int version, int newVersion) async {
+    if (version < 2) {
+      await db.execute('''
+              alter table projects add column archived boolean not null default false
+            ''');
+    }
+    if (version < 3) {
+      await db.execute('''
+              alter table timers add column notes text default null
+            ''');
+    }
+    if (version < 4) {
+      // fix the bug of the default value being `false` for project archives instead of `0`.
+      // `false` works fine on sqlite >= 3.23.0. Unfortunately, some Android phones still have
+      // ancient sqlite versions, so to them `false` is a string rather than an integer with
+      // value `0`
+      Batch b = db.batch();
+      b.execute('''
+            create table projects_tmp(
+                id integer not null primary key autoincrement,
+                name text not null,
+                colour int not null,
+                archived boolean not null default 0
+            )
+            ''');
+      b.execute("insert into projects_tmp select * from projects");
+      b.execute("drop table projects");
+      b.execute('''
+            create table projects(
+                id integer not null primary key autoincrement,
+                name text not null,
+                colour int not null,
+                archived boolean not null default 0
+            )
+        ''');
+      b.execute('''
+            insert into projects select id, name, colour,
+                case archived
+                    when 'false' then 0
+                    when 'true' then 1
+                    when '0' then 0
+                    when '1' then 1
+                    when 0 then 0
+                    when 1 then 1
+                    else 0
+                end as archived
+                from projects_tmp
+        ''');
+      b.execute("drop table projects_tmp");
+      await b.commit(noResult: true);
+    }
+  }
+
+  static Future<DatabaseProvider> open(String path) async {
+    // open the database
+    Database db = await openDatabase(path,
+        onConfigure: _onConfigure,
+        onCreate: _onCreate,
+        onUpgrade: _onUpgrade,
+        version: _dbVersion);
+    await db.execute("PRAGMA foreign_keys = ON");
+    DatabaseProvider repo = DatabaseProvider(db);
+
+    return repo;
+  }
+
+  /// the c in crud
+  @override
+  Future<Project> createProject(
+      {required String name, Color? colour, bool? archived}) async {
+    colour ??= Color.fromARGB(255, 60, 108, 186);
+    archived ??= false;
+
+    int id = await _db.rawInsert(
+        "insert into projects(name, colour, archived) values(?, ?, ?)",
+        <dynamic>[name, colour.value, archived ? 1 : 0]);
+    return Project(id: id, name: name, colour: colour, archived: archived);
+  }
+
+  /// the r in crud
+  @override
+  Future<List<Project>> listProjects() async {
+    List<Map<String, dynamic>> rawProjects = await _db.rawQuery('''
+        select id, name, colour, 
+            case archived
+                when 'false' then 0
+                when 'true' then 1
+                when '0' then 0
+                when '1' then 1
+                when 0 then 0
+                when 1 then 1
+                else 0
+            end as archived
+        from projects order by name asc
+    ''');
+    return rawProjects
+        .map((Map<String, dynamic> row) => Project(
+            id: row["id"] as int,
+            name: row["name"] as String,
+            colour: Color(row["colour"] as int),
+            archived: (row["archived"] as int?) == 1))
+        .toList();
+  }
+
+  /// the u in crud
+  @override
+  Future<void> editProject(Project project) async {
+    int rows = await _db.rawUpdate(
+        "update projects set name=?, colour=?, archived=? where id=?",
+        <dynamic>[
+          project.name,
+          project.colour,
+          project.archived ? 1 : 0,
+          project.id
+        ]);
+    assert(rows == 1);
+  }
+
+  /// the d in crud
+  @override
+  Future<void> deleteProject(Project project) async {
+    await _db
+        .rawDelete("delete from projects where id=?", <dynamic>[project.id]);
+  }
+
+  /// the c in crud
+  @override
+  Future<TimerEntry> createTimer(
+      {String? description,
+      int? projectID,
+      DateTime? startTime,
+      DateTime? endTime,
+      String? notes}) async {
+    int st = startTime?.millisecondsSinceEpoch ??
+        DateTime.now().millisecondsSinceEpoch;
+    int? et = endTime?.millisecondsSinceEpoch;
+    int id = await _db.rawInsert(
+        "insert into timers(project_id, description, start_time, end_time, notes) values(?, ?, ?, ?, ?)",
+        <dynamic>[projectID, description, st, et, notes]);
+    return TimerEntry(
+        id: id,
+        description: description,
+        projectID: projectID,
+        startTime: DateTime.fromMillisecondsSinceEpoch(st),
+        endTime: endTime,
+        notes: notes);
+  }
+
+  /// the r in crud
+  @override
+  Future<List<TimerEntry>> listTimers() async {
+    List<Map<String, dynamic>> rawTimers = await _db.rawQuery(
+        "select id, project_id, description, start_time, end_time, notes from timers order by start_time asc");
+    return rawTimers
+        .map((Map<String, dynamic> row) => TimerEntry(
+            id: row["id"] as int,
+            projectID: row["project_id"] as int?,
+            description: row["description"] as String?,
+            startTime:
+                DateTime.fromMillisecondsSinceEpoch(row["start_time"] as int),
+            endTime: row["end_time"] != null
+                ? DateTime.fromMillisecondsSinceEpoch(row["end_time"] as int)
+                : null,
+            notes: row["notes"] as String?))
+        .toList();
+  }
+
+  /// the u in crud
+  @override
+  Future<void> editTimer(TimerEntry timer) async {
+    int st = timer.startTime.millisecondsSinceEpoch;
+    int? et = timer.endTime?.millisecondsSinceEpoch;
+    await _db.rawUpdate(
+        "update timers set project_id=?, description=?, start_time=?, end_time=?, notes=? where id=?",
+        <dynamic>[
+          timer.projectID,
+          timer.description,
+          st,
+          et,
+          timer.notes,
+          timer.id
+        ]);
+  }
+
+  /// the d in crud
+  @override
+  Future<void> deleteTimer(TimerEntry timer) async {
+    await _db.rawDelete("delete from timers where id=?", <dynamic>[timer.id]);
+  }
+
+  static Future<File> getDatabaseFile() async {
+    final dbPath =
+        (Platform.isLinux) ? dataHome.path : await getDatabasesPath();
+    return File(p.join(dbPath, 'timecop.db'));
+  }
+
+  static Future<bool> isValidDatabaseFile(String path) async {
+    try {
+      Database db = await openDatabase(path, readOnly: true);
+      await db.rawQuery(
+          "select id, name, colour, archived from projects order by name asc limit 1");
+      await db.rawQuery(
+          "select id, project_id, description, start_time, end_time, notes from timers order by start_time asc limit 1");
+      await db.close();
+      return true;
+    } on Exception catch (_) {
+      return false;
+    }
+  }
+}
diff --git a/lib/db/mock_data_provider.dart b/lib/db/mock_data_provider.dart
new file mode 100644
index 0000000..9e3efcd
--- /dev/null
+++ b/lib/db/mock_data_provider.dart
@@ -0,0 +1,166 @@
+import 'package:flutter/material.dart';
+import 'package:timemanage/db/data_provider.dart';
+import 'package:timemanage/model/project.dart';
+import 'package:timemanage/model/timer_entry.dart';
+import 'dart:math';
+
+class MockDataProvider extends DataProvider {
+  String localeKey;
+  static final Map<String, Map<String, String>> l10n = {
+    "en": {
+      "administration": "Administration",
+      "mockups": "Mockups",
+      "ui-layout": "UI Layout",
+      "coffee": "Coffee",
+      "app-development": "App development"
+    },
+    "zh-CN": {
+      "ui-layout": "UI布局",
+      "administration": "管理",
+      "coffee": "咖啡",
+      "mockups": "样机",
+      "app-development": "应用程式开发",
+    },
+  };
+
+  MockDataProvider(Locale locale) : localeKey = locale.languageCode {
+    if (locale.languageCode == "zh") {
+      localeKey += "-${locale.countryCode!}";
+    }
+  }
+
+  @override
+  Future<List<Project>> listProjects() async {
+    return <Project>[
+      Project(
+          id: 1,
+          name: "Time Manager",
+          colour: Colors.cyan[600]!,
+          archived: false),
+      Project(
+        id: 2,
+        name: l10n[localeKey]!["administration"]!,
+        colour: Colors.pink[600]!,
+        archived: false,
+      ),
+    ];
+  }
+
+  @override
+  Future<List<TimerEntry>> listTimers() async {
+    int tid = 1;
+    Random rand = Random(42);
+
+    // start with running timers
+    List<TimerEntry> entries = [
+      TimerEntry(
+        id: tid++,
+        description: l10n[localeKey]!["ui-layout"],
+        projectID: 1,
+        startTime: DateTime.now()
+            .subtract(const Duration(hours: 2, minutes: 10, seconds: 1)),
+        endTime: null,
+      ),
+      TimerEntry(
+        id: tid++,
+        description: l10n[localeKey]!["coffee"],
+        projectID: 2,
+        startTime:
+            DateTime.now().subtract(const Duration(minutes: 3, seconds: 14)),
+        endTime: null,
+      ),
+    ];
+
+    // add some fake March stuff
+    for (int w = 0; w < 4; w++) {
+      for (int d = 0; d < 5; d++) {
+        String descriptionKey;
+        double r = rand.nextDouble();
+        if (r <= 0.2) {
+          descriptionKey = 'mockups';
+        } else if (r <= 0.5) {
+          descriptionKey = 'ui-layout';
+        } else {
+          descriptionKey = 'app-development';
+        }
+
+        entries.add(TimerEntry(
+          id: tid++,
+          description: l10n[localeKey]![descriptionKey],
+          projectID: 1,
+          startTime: DateTime(
+            2020,
+            3,
+            (w * 7) + d + 2,
+            rand.nextInt(3) + 8,
+            rand.nextInt(60),
+            rand.nextInt(60),
+          ),
+          endTime: DateTime(
+            2020,
+            3,
+            (w * 7) + d + 2,
+            rand.nextInt(3) + 13,
+            rand.nextInt(60),
+            rand.nextInt(60),
+          ),
+        ));
+
+        entries.add(TimerEntry(
+          id: tid++,
+          description: l10n[localeKey]!['administration'],
+          projectID: 2,
+          startTime: DateTime(
+            2020,
+            3,
+            (w * 7) + d + 2,
+            14,
+            rand.nextInt(30),
+            rand.nextInt(60),
+          ),
+          endTime: DateTime(
+            2020,
+            3,
+            (w * 7) + d + 2,
+            15,
+            rand.nextInt(30),
+            rand.nextInt(60),
+          ),
+        ));
+      }
+    }
+    return entries;
+  }
+
+  @override
+  Future<Project> createProject(
+      {required String name, Color? colour, bool? archived}) async {
+    return Project(
+        id: -1, name: name, colour: colour!, archived: archived ?? false);
+  }
+
+  @override
+  Future<void> editProject(Project project) async {}
+  @override
+  Future<void> deleteProject(Project project) async {}
+  @override
+  Future<TimerEntry> createTimer(
+      {String? description,
+      int? projectID,
+      DateTime? startTime,
+      DateTime? endTime}) async {
+    DateTime st = startTime ?? DateTime.now();
+    return TimerEntry(
+      id: -1,
+      description: description,
+      projectID: projectID,
+      startTime: st,
+      endTime: endTime,
+    );
+  }
+
+  @override
+  Future<void> editTimer(TimerEntry timer) async {}
+  @override
+  Future<void> deleteTimer(TimerEntry timer) async {}
+}
diff --git a/lib/model/project.dart b/lib/model/project.dart
index b18fd4e..edf4ce4 100644
--- a/lib/model/project.dart
+++ b/lib/model/project.dart
@@ -4,12 +4,14 @@ import 'package:equatable/equatable.dart'; // 比较两个对象是否相等的
 class Project extends Equatable {
   final int id;
   final String name;
+  final Color? colour; // 颜色
   final bool archived; // 是否归档
 
   // 构造函数
   const Project({
     required this.id,
     required this.name,
+    required this.colour,
     required this.archived,
   });
 
@@ -24,6 +26,7 @@ class Project extends Equatable {
   }) : this(
           id: project.id,
           name: name ?? project.name,
+          colour: color ?? project.colour,
           archived: archived ?? project.archived,
         );
 }
diff --git a/macos/Flutter/GeneratedPluginRegistrant.swift b/macos/Flutter/GeneratedPluginRegistrant.swift
index 744bfe9..97ce740 100644
--- a/macos/Flutter/GeneratedPluginRegistrant.swift
+++ b/macos/Flutter/GeneratedPluginRegistrant.swift
@@ -6,9 +6,11 @@ import FlutterMacOS
 import Foundation
 
 import package_info_plus
+import sqflite
 import url_launcher_macos
 
 func RegisterGeneratedPlugins(registry: FlutterPluginRegistry) {
   FLTPackageInfoPlusPlugin.register(with: registry.registrar(forPlugin: "FLTPackageInfoPlusPlugin"))
+  SqflitePlugin.register(with: registry.registrar(forPlugin: "SqflitePlugin"))
   UrlLauncherPlugin.register(with: registry.registrar(forPlugin: "UrlLauncherPlugin"))
 }
diff --git a/pubspec.lock b/pubspec.lock
index 7207144..a185836 100644
--- a/pubspec.lock
+++ b/pubspec.lock
@@ -333,6 +333,22 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.10.0"
+  sqflite:
+    dependency: "direct main"
+    description:
+      name: sqflite
+      sha256: "591f1602816e9c31377d5f008c2d9ef7b8aca8941c3f89cc5fd9d84da0c38a9a"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.3.0"
+  sqflite_common:
+    dependency: transitive
+    description:
+      name: sqflite_common
+      sha256: "1b92f368f44b0dee2425bb861cfa17b6f6cf3961f762ff6f941d20b33355660a"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.5.0"
   stack_trace:
     dependency: transitive
     description:
@@ -357,6 +373,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.2.0"
+  synchronized:
+    dependency: transitive
+    description:
+      name: synchronized
+      sha256: "5fcbd27688af6082f5abd611af56ee575342c30e87541d0245f7ff99faa02c60"
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.1.0"
   term_glyph:
     dependency: transitive
     description:
@@ -493,6 +517,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "5.0.8"
+  xdg_directories:
+    dependency: "direct main"
+    description:
+      name: xdg_directories
+      sha256: "589ada45ba9e39405c198fe34eb0f607cddb2108527e658136120892beac46d2"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.0.3"
   xml:
     dependency: transitive
     description:
diff --git a/pubspec.yaml b/pubspec.yaml
index 668033e..9c6ae8c 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -37,6 +37,8 @@ dependencies:
   font_awesome_flutter: ^9.2.0
   url_launcher: ^6.1.14
   equatable: ^2.0.3 # 用于对象比较
+  sqflite: ^2.0.0+3
+  xdg_directories: ^1.0.0
 
   # The following adds the Cupertino Icons font to your application.
   # Use with the CupertinoIcons class for iOS style icons.