diff --git a/matemat/db/__init__.py b/matemat/db/__init__.py
index a0697c9..0f2bc0a 100644
--- a/matemat/db/__init__.py
+++ b/matemat/db/__init__.py
@@ -1,2 +1,3 @@
 
-from .database import Database
+from .wrapper import DatabaseWrapper
+from .facade import DatabaseFacade as Database
diff --git a/matemat/db/database.py b/matemat/db/facade.py
similarity index 60%
rename from matemat/db/database.py
rename to matemat/db/facade.py
index c297721..6056e7c 100644
--- a/matemat/db/database.py
+++ b/matemat/db/facade.py
@@ -1,142 +1,31 @@
 
 from typing import List, Optional
 
-import apsw
 import bcrypt
 
 from matemat.primitives import User, Product
-from matemat.exceptions import AuthenticationException
+from matemat.exceptions import AuthenticationError, DatabaseConsistencyError
+from matemat.db import DatabaseWrapper
 
 
-class Transaction(object):
-
-    def __init__(self, db: apsw.Connection, wrapper: 'Database', exclusive: bool = True):
-        self._db: apsw.Connection = db
-        self._cursor = None
-        self._excl = exclusive
-        self._wrapper: Database = wrapper
-        self._is_dummy: bool = False
-
-    def __enter__(self):
-        if self._wrapper._in_transaction:
-            self._is_dummy = True
-            return self._db.cursor()
-        else:
-            self._is_dummy = False
-        self._cursor = self._db.cursor()
-        self._wrapper._in_transaction = True
-        if self._excl:
-            self._cursor.execute('BEGIN EXCLUSIVE')
-        else:
-            self._cursor.execute('BEGIN')
-        return self._cursor
-
-    def __exit__(self, exc_type, exc_val, exc_tb):
-        if self._is_dummy:
-            return
-        if exc_type is None:
-            self._cursor.execute('COMMIT')
-        else:
-            self._cursor.execute('ROLLBACK')
-        self._wrapper._in_transaction = False
-
-
-class Database(object):
-    SCHEMA_VERSION = 1
-
-    SCHEMA = '''
-    CREATE TABLE users (
-      user_id INTEGER PRIMARY KEY,
-      username TEXT NOT NULL,
-      email TEXT DEFAULT NULL,
-      password TEXT NOT NULL,
-      touchkey TEXT DEFAULT NULL,
-      is_admin INTEGER(1) NOT NULL DEFAULT 0,
-      is_member INTEGER(1) NOT NULL DEFAULT 1,
-      balance INTEGER(8) NOT NULL DEFAULT 0,
-      lastchange INTEGER(8) NOT NULL DEFAULT 0
-    );
-    CREATE TABLE products (
-      product_id INTEGER PRIMARY KEY,
-      name TEXT UNIQUE NOT NULL,
-      stock INTEGER(8) NOT NULL DEFAULT 0,
-      price_member INTEGER(8) NOT NULL,
-      price_non_member INTEGER(8) NOT NULL
-    );
-    CREATE TABLE consumption (
-      user_id INTEGER NOT NULL,
-      product_id INTEGER NOT NULL,
-      count INTEGER(8) NOT NULL DEFAULT 0,
-      PRIMARY KEY (user_id, product_id),
-      FOREIGN KEY (user_id) REFERENCES users(user_id)
-        ON DELETE CASCADE ON UPDATE CASCADE,
-      FOREIGN KEY (product_id) REFERENCES products(product_id)
-        ON DELETE CASCADE ON UPDATE CASCADE
-    )
-    '''
+class DatabaseFacade(object):
 
     def __init__(self, filename: str):
-        self._filename: str = filename
-        self._sqlite_db: apsw.Connection = None
-        self._in_transaction: bool = False
+        self.db: DatabaseWrapper = DatabaseWrapper(filename)
 
     def __enter__(self):
-        self.connect()
+        self.db.__enter__()
         return self
 
     def __exit__(self, exc_type, exc_val, exc_tb):
-        self.close()
+        self.db.__exit__(exc_type, exc_val, exc_tb)
 
-    def transaction(self, exclusive: bool = True) -> Transaction:
-        return Transaction(self._sqlite_db, self, exclusive)
-
-    def _setup(self):
-        with self.transaction() as c:
-            version: int = self._user_version
-            if version < 1:
-                c.execute(self.SCHEMA)
-            elif version < self.SCHEMA_VERSION:
-                self._upgrade(old=version, new=self.SCHEMA_VERSION)
-            self._user_version = self.SCHEMA_VERSION
-
-    def _upgrade(self, old: int, new: int):
-        pass
-
-    def connect(self):
-        if self.is_connected():
-            raise RuntimeError(f'Database connection to {self._filename} is already established.')
-        self._sqlite_db = apsw.Connection(self._filename)
-        self._setup()
-
-    def close(self):
-        if self._sqlite_db is None:
-            raise RuntimeError(f'Database connection to {self._filename} is not established.')
-        if self.in_transaction():
-            raise RuntimeError(f'A transaction is still ongoing.')
-        self._sqlite_db.close()
-        self._sqlite_db = None
-
-    def in_transaction(self) -> bool:
-        return self._in_transaction
-
-    def is_connected(self) -> bool:
-        return self._sqlite_db is not None
-
-    @property
-    def _user_version(self) -> int:
-        cursor = self._sqlite_db.cursor()
-        cursor.execute('PRAGMA user_version')
-        version = int(cursor.fetchone()[0])
-        return version
-
-    @_user_version.setter
-    def _user_version(self, version: int):
-        cursor = self._sqlite_db.cursor()
-        cursor.execute(f'PRAGMA user_version = {version}')
+    def transaction(self, exclusive: bool = True):
+        return self.db.transaction(exclusive=exclusive)
 
     def list_users(self) -> List[User]:
         users: List[User] = []
-        with self.transaction(exclusive=False) as c:
+        with self.db.transaction(exclusive=False) as c:
             for row in c.execute('''
                 SELECT user_id, username, email, is_admin, is_member
                 FROM users
@@ -153,7 +42,7 @@ class Database(object):
                     member: bool = True) -> User:
         pwhash: str = bcrypt.hashpw(password.encode('utf-8'), bcrypt.gensalt(12))
         user_id: int = -1
-        with self.transaction() as c:
+        with self.db.transaction() as c:
             c.execute('SELECT user_id FROM users WHERE username = ?', [username])
             if c.fetchone() is not None:
                 raise ValueError(f'A user with the name \'{username}\' already exists.')
@@ -167,37 +56,43 @@ class Database(object):
                 'admin': admin,
                 'member': member
             })
+            affected = c.execute('SELECT changes()').fetchone()[0]
+            if affected != 1:
+                raise DatabaseConsistencyError(
+                    f'create_user should affect 1 users row, but affected {affected}')
             c.execute('SELECT last_insert_rowid()')
             user_id = int(c.fetchone()[0])
         return User(user_id, username, email, admin, member)
 
-    def login(self, username: str, password: str) -> Optional[User]:
-        with self.transaction(exclusive=False) as c:
+    def login(self, username: str, password: Optional[str] = None, touchkey: Optional[str] = None) -> User:
+        if (password is None) == (touchkey is None):
+            raise ValueError('Exactly one of password and touchkey must be provided')
+        with self.db.transaction(exclusive=False) as c:
             c.execute('''
-              SELECT user_id, username, email, password, is_admin, is_member
+              SELECT user_id, username, email, password, touchkey, is_admin, is_member
               FROM users
               WHERE username = ?
               ''', [username])
             row = c.fetchone()
             if row is None:
-                return None
-            user_id, username, email, pwhash, admin, member = row
-            if not bcrypt.checkpw(password.encode('utf-8'), pwhash):
-                return None
+                raise AuthenticationError('User does not exist')
+            user_id, username, email, pwhash, tkhash, admin, member = row
+            if password is not None and not bcrypt.checkpw(password.encode('utf-8'), pwhash):
+                raise AuthenticationError('Password mismatch')
+            elif touchkey is not None and not bcrypt.checkpw(touchkey.encode('utf-8'), tkhash):
+                raise AuthenticationError('Touchkey mismatch')
             return User(user_id, username, email, admin, member)
 
-    def change_password(self, user: User, oldpass: str, newpass: str, newpass2: str, verify_password: bool = True):
-        if newpass != newpass2:
-            raise ValueError('New passwords don\'t match.')
-        with self.transaction() as c:
+    def change_password(self, user: User, oldpass: str, newpass: str, verify_password: bool = True):
+        with self.db.transaction() as c:
             c.execute('''
             SELECT password FROM users WHERE user_id = ?
             ''', [user.id])
             row = c.fetchone()
             if row is None:
-                raise AuthenticationException('User does not exist in database.')
+                raise AuthenticationError('User does not exist in database.')
             if verify_password and not bcrypt.checkpw(oldpass.encode('utf-8'), row[0]):
-                raise AuthenticationException('Old password does not match.')
+                raise AuthenticationError('Old password does not match.')
             pwhash: str = bcrypt.hashpw(newpass.encode('utf-8'), bcrypt.gensalt(12))
             c.execute('''
             UPDATE users SET password = :pwhash, lastchange = STRFTIME('%s', 'now') WHERE user_id = :user_id
@@ -205,17 +100,21 @@ class Database(object):
                 'user_id': user.id,
                 'pwhash': pwhash
             })
+            affected = c.execute('SELECT changes()').fetchone()[0]
+            if affected != 1:
+                raise DatabaseConsistencyError(
+                    f'change_password should affect 1 users row, but affected {affected}')
 
     def change_touchkey(self, user: User, password: str, touchkey: Optional[str], verify_password: bool = True):
-        with self.transaction() as c:
+        with self.db.transaction() as c:
             c.execute('''
             SELECT password FROM users WHERE user_id = ?
             ''', [user.id])
             row = c.fetchone()
             if row is None:
-                raise AuthenticationException('User does not exist in database.')
+                raise AuthenticationError('User does not exist in database.')
             if verify_password and not bcrypt.checkpw(password.encode('utf-8'), row[0]):
-                raise AuthenticationException('Password does not match.')
+                raise AuthenticationError('Password does not match.')
             tkhash: str = bcrypt.hashpw(touchkey.encode('utf-8'), bcrypt.gensalt(12)) if touchkey is not None else None
             c.execute('''
             UPDATE users SET touchkey = :tkhash, lastchange = STRFTIME('%s', 'now') WHERE user_id = :user_id
@@ -223,9 +122,13 @@ class Database(object):
                 'user_id': user.id,
                 'tkhash': tkhash
             })
+            affected = c.execute('SELECT changes()').fetchone()[0]
+            if affected != 1:
+                raise DatabaseConsistencyError(
+                    f'change_touchkey should affect 1 users row, but affected {affected}')
 
     def change_user(self, user: User):
-        with self.transaction() as c:
+        with self.db.transaction() as c:
             c.execute('''
             UPDATE users SET
               email = :email,
@@ -239,17 +142,25 @@ class Database(object):
                 'is_admin': user.is_admin,
                 'is_member': user.is_member
             })
+            affected = c.execute('SELECT changes()').fetchone()[0]
+            if affected != 1:
+                raise DatabaseConsistencyError(
+                    f'change_user should affect 1 users row, but affected {affected}')
 
     def delete_user(self, user: User):
-        with self.transaction() as c:
+        with self.db.transaction() as c:
             c.execute('''
             DELETE FROM users
             WHERE user_id = ?
             ''', [user.id])
+            affected = c.execute('SELECT changes()').fetchone()[0]
+            if affected != 1:
+                raise DatabaseConsistencyError(
+                    f'delete_user should affect 1 users row, but affected {affected}')
 
     def list_products(self) -> List[Product]:
         products: List[Product] = []
-        with self.transaction(exclusive=False) as c:
+        with self.db.transaction(exclusive=False) as c:
             for row in c.execute('''
                 SELECT product_id, name, price_member, price_external
                 FROM products
@@ -260,7 +171,7 @@ class Database(object):
 
     def create_product(self, name: str, price_member: int, price_non_member: int) -> Product:
         product_id: int = -1
-        with self.transaction() as c:
+        with self.db.transaction() as c:
             c.execute('SELECT product_id FROM products WHERE name = ?', [name])
             if c.fetchone() is not None:
                 raise ValueError(f'A product with the name \'{name}\' already exists.')
@@ -273,13 +184,17 @@ class Database(object):
                 'price_non_member': price_non_member
             })
             c.execute('SELECT last_insert_rowid()')
+            affected = c.execute('SELECT changes()').fetchone()[0]
+            if affected != 1:
+                raise DatabaseConsistencyError(
+                    f'create_product should affect 1 products row, but affected {affected}')
             product_id = int(c.fetchone()[0])
         return Product(product_id, name, price_member, price_non_member)
 
     def change_product(self, product: Product):
         if product.id == -1:
             raise ValueError('Invalid product ID')
-        with self.transaction() as c:
+        with self.db.transaction() as c:
             c.execute('''
             UPDATE products
             SET
@@ -292,20 +207,24 @@ class Database(object):
                 'price_member': product.price_member,
                 'price_non_member': product.price_non_member
             })
+            affected = c.execute('SELECT changes()').fetchone()[0]
+            if affected != 1:
+                raise DatabaseConsistencyError(
+                    f'change_product should affect 1 products row, but affected {affected}')
 
     def delete_product(self, product: Product):
-        if product.id == -1:
-            raise ValueError('Invalid product ID')
-        with self.transaction() as c:
+        with self.db.transaction() as c:
             c.execute('''
             DELETE FROM products
             WHERE product_id = ?
             ''', [product.id])
+            affected = c.execute('SELECT changes()').fetchone()[0]
+            if affected != 1:
+                raise DatabaseConsistencyError(
+                    f'delete_product should affect 1 products row, but affected {affected}')
 
     def increment_consumption(self, user: User, product: Product, count: int = 1):
-        if product.id == -1:
-            raise ValueError('Invalid product ID')
-        with self.transaction() as c:
+        with self.db.transaction() as c:
             c.execute('''
             SELECT count
             FROM consumption
@@ -332,6 +251,10 @@ class Database(object):
                     'product_id': product.id,
                     'count': count
                 })
+            affected = c.execute('SELECT changes()').fetchone()[0]
+            if affected != 1:
+                raise DatabaseConsistencyError(
+                    f'increment_consumption should affect 1 consumption row, but affected {affected}')
             c.execute('''
             UPDATE users
             SET balance = balance - :cost
@@ -339,6 +262,10 @@ class Database(object):
                 'user_id': user.id,
                 'cost': count * product.price_member if user.is_member else count * product.price_non_member
             })
+            affected = c.execute('SELECT changes()').fetchone()[0]
+            if affected != 1:
+                raise DatabaseConsistencyError(
+                    f'increment_consumption should affect 1 users row, but affected {affected}')
             c.execute('''
             UPDATE products
             SET stock = stock - :count
@@ -347,11 +274,15 @@ class Database(object):
                 'product_id': product.id,
                 'count': count
             })
+            affected = c.execute('SELECT changes()').fetchone()[0]
+            if affected != 1:
+                raise DatabaseConsistencyError(
+                    f'increment_consumption should affect 1 products row, but affected {affected}')
 
     def restock(self, product: Product, count: int):
         if product.id == -1:
             raise ValueError('Invalid product ID')
-        with self.transaction() as c:
+        with self.db.transaction() as c:
             c.execute('''
             UPDATE products
             SET stock = stock + :count
@@ -360,9 +291,12 @@ class Database(object):
                 'product_id': product.id,
                 'count': count
             })
+            affected = c.execute('SELECT changes()').fetchone()[0]
+            if affected != 1:
+                raise DatabaseConsistencyError(f'restock should affect 1 products row, but affected {affected}')
 
     def deposit(self, user: User, amount: int):
-        with self.transaction() as c:
+        with self.db.transaction() as c:
             c.execute('''
             UPDATE users
             SET balance = balance + :amount
@@ -371,3 +305,6 @@ class Database(object):
                 'user_id': user.id,
                 'amount': amount
             })
+            affected = c.execute('SELECT changes()').fetchone()[0]
+            if affected != 1:
+                raise DatabaseConsistencyError(f'deposit should affect 1 users row, but affected {affected}')
diff --git a/matemat/db/test/test_facade.py b/matemat/db/test/test_facade.py
new file mode 100644
index 0000000..049edcb
--- /dev/null
+++ b/matemat/db/test/test_facade.py
@@ -0,0 +1,69 @@
+
+import unittest
+
+from matemat.db import Database
+from matemat.exceptions import AuthenticationError, DatabaseConsistencyError
+
+
+class DatabaseTest(unittest.TestCase):
+
+    def setUp(self):
+        self.db = Database(':memory:')
+
+    def test_create_user(self):
+        with self.db as db:
+            with db.transaction() as c:
+                db.create_user('testuser', 'supersecurepassword', 'testuser@example.com')
+                c.execute("SELECT * FROM users")
+                row = c.fetchone()
+                if row is None:
+                    self.fail()
+                self.assertEqual('testuser', row[1])
+                self.assertEqual('testuser@example.com', row[2])
+                self.assertEqual(0, row[5])
+                self.assertEqual(1, row[6])
+
+    def test_create_existing_user(self):
+        with self.db as db:
+            db.create_user('testuser', 'supersecurepassword', 'testuser@example.com')
+            with self.assertRaises(ValueError):
+                db.create_user('testuser', 'supersecurepassword2', 'testuser2@example.com')
+
+    def test_change_password(self):
+        with self.db as db:
+            user = db.create_user('testuser', 'supersecurepassword', 'testuser@example.com')
+            db.login('testuser', 'supersecurepassword')
+            # Normal password change should succeed
+            db.change_password(user, 'supersecurepassword', 'mynewpassword')
+            with self.assertRaises(AuthenticationError):
+                db.login('testuser', 'supersecurepassword')
+            db.login('testuser', 'mynewpassword')
+            with self.assertRaises(AuthenticationError):
+                # Should fail due to wrong old password
+                db.change_password(user, 'iforgotmypassword', 'mynewpassword')
+            db.login('testuser', 'mynewpassword')
+            # This should pass even though the old password is not known (admin password reset)
+            db.change_password(user, '42', 'adminpasswordreset', verify_password=False)
+            with self.assertRaises(AuthenticationError):
+                db.login('testuser', 'mynewpassword')
+            db.login('testuser', 'adminpasswordreset')
+
+    def test_change_touchkey(self):
+        with self.db as db:
+            user = db.create_user('testuser', 'supersecurepassword', 'testuser@example.com')
+            db.change_touchkey(user, 'supersecurepassword', '0123')
+            db.login('testuser', touchkey='0123')
+            # Normal touchkey change should succeed
+            db.change_touchkey(user, 'supersecurepassword', touchkey='4567')
+            with self.assertRaises(AuthenticationError):
+                db.login('testuser', touchkey='0123')
+            db.login('testuser', touchkey='4567')
+            with self.assertRaises(AuthenticationError):
+                # Should fail due to wrong old password
+                db.change_touchkey(user, 'iforgotmypassword', '89ab')
+            db.login('testuser', touchkey='4567')
+            # This should pass even though the old password is not known (admin password reset)
+            db.change_touchkey(user, '42', '89ab', verify_password=False)
+            with self.assertRaises(AuthenticationError):
+                db.login('testuser', touchkey='4567')
+            db.login('testuser', touchkey='89ab')
diff --git a/matemat/db/test/test_database.py b/matemat/db/test/test_wrapper.py
similarity index 71%
rename from matemat/db/test/test_database.py
rename to matemat/db/test/test_wrapper.py
index a03fbd4..334ecdf 100644
--- a/matemat/db/test/test_database.py
+++ b/matemat/db/test/test_wrapper.py
@@ -1,20 +1,20 @@
 
 import unittest
 
-from matemat.db import Database
+from matemat.db import DatabaseWrapper
 
 
 class DatabaseTest(unittest.TestCase):
 
     def setUp(self):
-        self.db = Database(':memory:')
+        self.db = DatabaseWrapper(':memory:')
 
     def test_create_schema(self):
         """
         Test creation of database schema in an empty database
         """
         with self.db as db:
-            self.assertEqual(Database.SCHEMA_VERSION, db._user_version)
+            self.assertEqual(DatabaseWrapper.SCHEMA_VERSION, db._user_version)
 
     def test_in_transaction(self):
         """
@@ -74,22 +74,3 @@ class DatabaseTest(unittest.TestCase):
             c = db._sqlite_db.cursor()
             c.execute("SELECT * FROM users")
             self.assertIsNone(c.fetchone())
-
-    def test_create_user(self):
-        with self.db as db:
-            with db.transaction() as c:
-                db.create_user('testuser', 'supersecurepassword', 'testuser@example.com')
-                c.execute("SELECT * FROM users")
-                row = c.fetchone()
-                if row is None:
-                    self.fail()
-                self.assertEqual('testuser', row[1])
-                self.assertEqual('testuser@example.com', row[2])
-                self.assertEqual(0, row[5])
-                self.assertEqual(1, row[6])
-
-    def test_create_existing_user(self):
-        with self.db as db:
-            db.create_user('testuser', 'supersecurepassword', 'testuser@example.com')
-            with self.assertRaises(ValueError):
-                db.create_user('testuser', 'supersecurepassword2', 'testuser2@example.com')
diff --git a/matemat/db/wrapper.py b/matemat/db/wrapper.py
new file mode 100644
index 0000000..3b92936
--- /dev/null
+++ b/matemat/db/wrapper.py
@@ -0,0 +1,129 @@
+
+import apsw
+
+
+class Transaction(object):
+
+    def __init__(self, db: apsw.Connection, wrapper: 'DatabaseWrapper', exclusive: bool = True):
+        self._db: apsw.Connection = db
+        self._cursor = None
+        self._excl = exclusive
+        self._wrapper: DatabaseWrapper = wrapper
+        self._is_dummy: bool = False
+
+    def __enter__(self):
+        if self._wrapper._in_transaction:
+            self._is_dummy = True
+            return self._db.cursor()
+        else:
+            self._is_dummy = False
+        self._cursor = self._db.cursor()
+        self._wrapper._in_transaction = True
+        if self._excl:
+            self._cursor.execute('BEGIN EXCLUSIVE')
+        else:
+            self._cursor.execute('BEGIN')
+        return self._cursor
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        if self._is_dummy:
+            return
+        if exc_type is None:
+            self._cursor.execute('COMMIT')
+        else:
+            self._cursor.execute('ROLLBACK')
+        self._wrapper._in_transaction = False
+
+
+class DatabaseWrapper(object):
+    SCHEMA_VERSION = 1
+
+    SCHEMA = '''
+    CREATE TABLE users (
+      user_id INTEGER PRIMARY KEY,
+      username TEXT NOT NULL,
+      email TEXT DEFAULT NULL,
+      password TEXT NOT NULL,
+      touchkey TEXT DEFAULT NULL,
+      is_admin INTEGER(1) NOT NULL DEFAULT 0,
+      is_member INTEGER(1) NOT NULL DEFAULT 1,
+      balance INTEGER(8) NOT NULL DEFAULT 0,
+      lastchange INTEGER(8) NOT NULL DEFAULT 0
+    );
+    CREATE TABLE products (
+      product_id INTEGER PRIMARY KEY,
+      name TEXT UNIQUE NOT NULL,
+      stock INTEGER(8) NOT NULL DEFAULT 0,
+      price_member INTEGER(8) NOT NULL,
+      price_non_member INTEGER(8) NOT NULL
+    );
+    CREATE TABLE consumption (
+      user_id INTEGER NOT NULL,
+      product_id INTEGER NOT NULL,
+      count INTEGER(8) NOT NULL DEFAULT 0,
+      PRIMARY KEY (user_id, product_id),
+      FOREIGN KEY (user_id) REFERENCES users(user_id)
+        ON DELETE CASCADE ON UPDATE CASCADE,
+      FOREIGN KEY (product_id) REFERENCES products(product_id)
+        ON DELETE CASCADE ON UPDATE CASCADE
+    )
+    '''
+
+    def __init__(self, filename: str):
+        self._filename: str = filename
+        self._sqlite_db: apsw.Connection = None
+        self._in_transaction: bool = False
+
+    def __enter__(self):
+        self.connect()
+        return self
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        self.close()
+
+    def transaction(self, exclusive: bool = True) -> Transaction:
+        return Transaction(self._sqlite_db, self, exclusive)
+
+    def _setup(self):
+        with self.transaction() as c:
+            version: int = self._user_version
+            if version < 1:
+                c.execute(self.SCHEMA)
+            elif version < self.SCHEMA_VERSION:
+                self._upgrade(old=version, new=self.SCHEMA_VERSION)
+            self._user_version = self.SCHEMA_VERSION
+
+    def _upgrade(self, old: int, new: int):
+        pass
+
+    def connect(self):
+        if self.is_connected():
+            raise RuntimeError(f'Database connection to {self._filename} is already established.')
+        self._sqlite_db = apsw.Connection(self._filename)
+        self._setup()
+
+    def close(self):
+        if self._sqlite_db is None:
+            raise RuntimeError(f'Database connection to {self._filename} is not established.')
+        if self.in_transaction():
+            raise RuntimeError(f'A transaction is still ongoing.')
+        self._sqlite_db.close()
+        self._sqlite_db = None
+
+    def in_transaction(self) -> bool:
+        return self._in_transaction
+
+    def is_connected(self) -> bool:
+        return self._sqlite_db is not None
+
+    @property
+    def _user_version(self) -> int:
+        cursor = self._sqlite_db.cursor()
+        cursor.execute('PRAGMA user_version')
+        version = int(cursor.fetchone()[0])
+        return version
+
+    @_user_version.setter
+    def _user_version(self, version: int):
+        cursor = self._sqlite_db.cursor()
+        cursor.execute(f'PRAGMA user_version = {version}')
diff --git a/matemat/exceptions/AuthenticatonException.py b/matemat/exceptions/AuthenticatonError.py
similarity index 61%
rename from matemat/exceptions/AuthenticatonException.py
rename to matemat/exceptions/AuthenticatonError.py
index 55eed7c..4494a33 100644
--- a/matemat/exceptions/AuthenticatonException.py
+++ b/matemat/exceptions/AuthenticatonError.py
@@ -1,11 +1,11 @@
 
-class AuthenticationException(BaseException):
+class AuthenticationError(BaseException):
 
     def __init__(self, msg: str = None):
         self._msg = msg
 
     def __str__(self) -> str:
-        return f'AuthenticationException: {self._msg}'
+        return f'AuthenticationErro: {self._msg}'
 
     @property
     def msg(self) -> str:
diff --git a/matemat/exceptions/DatabaseConsistencyError.py b/matemat/exceptions/DatabaseConsistencyError.py
new file mode 100644
index 0000000..d07d7a1
--- /dev/null
+++ b/matemat/exceptions/DatabaseConsistencyError.py
@@ -0,0 +1,12 @@
+
+class DatabaseConsistencyError(BaseException):
+
+    def __init__(self, msg: str = None):
+        self._msg = msg
+
+    def __str__(self) -> str:
+        return f'DatabaseConsistencyError: {self._msg}'
+
+    @property
+    def msg(self) -> str:
+        return self._msg
diff --git a/matemat/exceptions/__init__.py b/matemat/exceptions/__init__.py
index 08617cb..cacbbb9 100644
--- a/matemat/exceptions/__init__.py
+++ b/matemat/exceptions/__init__.py
@@ -1,2 +1,3 @@
 
-from .AuthenticatonException import AuthenticationException
+from .AuthenticatonError import AuthenticationError
+from .DatabaseConsistencyError import DatabaseConsistencyError