diff --git a/persistence/src/main/java/fr/gasser/daoexample/dao/Dao.java b/persistence/src/main/java/fr/gasser/daoexample/dao/Dao.java
index 44e746b..01fc055 100644
--- a/persistence/src/main/java/fr/gasser/daoexample/dao/Dao.java
+++ b/persistence/src/main/java/fr/gasser/daoexample/dao/Dao.java
@@ -1,16 +1,16 @@
 package fr.gasser.daoexample.dao;
 
 import fr.gasser.daoexample.model.Entity;
-import fr.gasser.daoexample.sql.Connection;
+import fr.gasser.daoexample.dao.connection.ConnectionWrapper;
 
 import java.util.List;
 
 public abstract class Dao<T extends Entity> {
 
-    protected Connection connection;
+    protected final ConnectionWrapper connectionWrapper;
 
-    public Dao(Connection connection) {
-        this.connection = connection;
+    protected Dao(ConnectionWrapper connectionWrapper) {
+        this.connectionWrapper = connectionWrapper;
     }
 
     public abstract boolean create(T obj);
diff --git a/persistence/src/main/java/fr/gasser/daoexample/dao/DaoAbstractFactory.java b/persistence/src/main/java/fr/gasser/daoexample/dao/DaoAbstractFactory.java
index 0eab54b..07c8d8a 100644
--- a/persistence/src/main/java/fr/gasser/daoexample/dao/DaoAbstractFactory.java
+++ b/persistence/src/main/java/fr/gasser/daoexample/dao/DaoAbstractFactory.java
@@ -1,5 +1,8 @@
 package fr.gasser.daoexample.dao;
 
+import fr.gasser.daoexample.dao.dummy.DaoFactory;
+import fr.gasser.daoexample.dao.dummy.FactoryType;
+import fr.gasser.daoexample.dao.sqlite.SqliteDaoFactory;
 import fr.gasser.daoexample.model.Discipline;
 import fr.gasser.daoexample.model.Student;
 import fr.gasser.daoexample.model.Teacher;
diff --git a/persistence/src/main/java/fr/gasser/daoexample/dao/DaoFactory.java b/persistence/src/main/java/fr/gasser/daoexample/dao/DaoFactory.java
deleted file mode 100644
index 77bc207..0000000
--- a/persistence/src/main/java/fr/gasser/daoexample/dao/DaoFactory.java
+++ /dev/null
@@ -1,26 +0,0 @@
-package fr.gasser.daoexample.dao;
-
-import fr.gasser.daoexample.model.Discipline;
-import fr.gasser.daoexample.model.Student;
-import fr.gasser.daoexample.model.Teacher;
-import fr.gasser.daoexample.sql.Connection;
-import fr.gasser.daoexample.sql.DummyConnection;
-
-public class DaoFactory implements DaoAbstractFactory {
-    private static Connection connection = new DummyConnection();
-
-    @Override
-    public Dao<Student> createStudentDao() {
-        return new StudentDao(DaoFactory.connection);
-    }
-
-    @Override
-    public Dao<Teacher> createTeacherDao() {
-        return new TeacherDao(DaoFactory.connection);
-    }
-
-    @Override
-    public Dao<Discipline> createDisciplineDao() {
-        return new DisciplineDao(DaoFactory.connection);
-    }
-}
diff --git a/persistence/src/main/java/fr/gasser/daoexample/dao/XmlDaoFactory.java b/persistence/src/main/java/fr/gasser/daoexample/dao/XmlDaoFactory.java
index 247d6a7..76344c3 100644
--- a/persistence/src/main/java/fr/gasser/daoexample/dao/XmlDaoFactory.java
+++ b/persistence/src/main/java/fr/gasser/daoexample/dao/XmlDaoFactory.java
@@ -1,18 +1,22 @@
 package fr.gasser.daoexample.dao;
 
+import fr.gasser.daoexample.model.Discipline;
+import fr.gasser.daoexample.model.Student;
+import fr.gasser.daoexample.model.Teacher;
+
 public class XmlDaoFactory implements DaoAbstractFactory {
     @Override
-    public StudentDao createStudentDao() {
+    public Dao<Student> createStudentDao() {
         return null;
     }
 
     @Override
-    public TeacherDao createTeacherDao() {
+    public Dao<Teacher> createTeacherDao() {
         return null;
     }
 
     @Override
-    public DisciplineDao createDisciplineDao() {
+    public Dao<Discipline> createDisciplineDao() {
         return null;
     }
 }
diff --git a/persistence/src/main/java/fr/gasser/daoexample/sql/Connection.java b/persistence/src/main/java/fr/gasser/daoexample/dao/connection/ConnectionWrapper.java
similarity index 65%
rename from persistence/src/main/java/fr/gasser/daoexample/sql/Connection.java
rename to persistence/src/main/java/fr/gasser/daoexample/dao/connection/ConnectionWrapper.java
index c610453..2c33474 100644
--- a/persistence/src/main/java/fr/gasser/daoexample/sql/Connection.java
+++ b/persistence/src/main/java/fr/gasser/daoexample/dao/connection/ConnectionWrapper.java
@@ -1,8 +1,8 @@
-package fr.gasser.daoexample.sql;
+package fr.gasser.daoexample.dao.connection;
 
 import java.sql.SQLException;
 
-public interface Connection {
+public interface ConnectionWrapper {
     void connect() throws SQLException;
 
     void close() throws SQLException;
diff --git a/persistence/src/main/java/fr/gasser/daoexample/sql/DummyConnection.java b/persistence/src/main/java/fr/gasser/daoexample/dao/connection/DummyConnectionWrapper.java
similarity index 63%
rename from persistence/src/main/java/fr/gasser/daoexample/sql/DummyConnection.java
rename to persistence/src/main/java/fr/gasser/daoexample/dao/connection/DummyConnectionWrapper.java
index 936647e..0590415 100644
--- a/persistence/src/main/java/fr/gasser/daoexample/sql/DummyConnection.java
+++ b/persistence/src/main/java/fr/gasser/daoexample/dao/connection/DummyConnectionWrapper.java
@@ -1,6 +1,6 @@
-package fr.gasser.daoexample.sql;
+package fr.gasser.daoexample.dao.connection;
 
-public class DummyConnection implements Connection {
+public class DummyConnectionWrapper implements ConnectionWrapper {
     @Override
     public void connect() {
 
diff --git a/persistence/src/main/java/fr/gasser/daoexample/sql/SQLiteConnectionException.java b/persistence/src/main/java/fr/gasser/daoexample/dao/connection/SQLiteConnectionException.java
similarity index 54%
rename from persistence/src/main/java/fr/gasser/daoexample/sql/SQLiteConnectionException.java
rename to persistence/src/main/java/fr/gasser/daoexample/dao/connection/SQLiteConnectionException.java
index c217ac1..9246187 100644
--- a/persistence/src/main/java/fr/gasser/daoexample/sql/SQLiteConnectionException.java
+++ b/persistence/src/main/java/fr/gasser/daoexample/dao/connection/SQLiteConnectionException.java
@@ -1,8 +1,8 @@
-package fr.gasser.daoexample.sql;
+package fr.gasser.daoexample.dao.connection;
 
 import java.sql.SQLException;
 
-public class SQLiteConnectionException extends SQLException {
+class SQLiteConnectionException extends SQLException {
     public SQLiteConnectionException(String message) {
         super(message);
     }
diff --git a/persistence/src/main/java/fr/gasser/daoexample/sql/SQLiteConnection.java b/persistence/src/main/java/fr/gasser/daoexample/dao/connection/SQLiteConnectionWrapper.java
similarity index 79%
rename from persistence/src/main/java/fr/gasser/daoexample/sql/SQLiteConnection.java
rename to persistence/src/main/java/fr/gasser/daoexample/dao/connection/SQLiteConnectionWrapper.java
index 2697fcd..772378d 100644
--- a/persistence/src/main/java/fr/gasser/daoexample/sql/SQLiteConnection.java
+++ b/persistence/src/main/java/fr/gasser/daoexample/dao/connection/SQLiteConnectionWrapper.java
@@ -1,4 +1,4 @@
-package fr.gasser.daoexample.sql;
+package fr.gasser.daoexample.dao.connection;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -6,17 +6,17 @@ import org.slf4j.LoggerFactory;
 import java.sql.DriverManager;
 import java.sql.SQLException;
 
-public class SQLiteConnection implements Connection {
-    private static final Logger LOGGER = LoggerFactory.getLogger(SQLiteConnection.class);
+public class SQLiteConnectionWrapper implements ConnectionWrapper {
+    private static final Logger LOGGER = LoggerFactory.getLogger(SQLiteConnectionWrapper.class);
 
-    private String dbpath;
+    private final String dbpath;
     private java.sql.Connection connection = null;
 
-    public SQLiteConnection(String dBPath) {
+    private SQLiteConnectionWrapper(String dBPath) {
         dbpath = dBPath;
     }
 
-    public SQLiteConnection() {
+    public SQLiteConnectionWrapper() {
         this(":memory:");
     }
 
diff --git a/persistence/src/main/java/fr/gasser/daoexample/dao/dummy/DaoFactory.java b/persistence/src/main/java/fr/gasser/daoexample/dao/dummy/DaoFactory.java
new file mode 100644
index 0000000..8dd21e7
--- /dev/null
+++ b/persistence/src/main/java/fr/gasser/daoexample/dao/dummy/DaoFactory.java
@@ -0,0 +1,28 @@
+package fr.gasser.daoexample.dao.dummy;
+
+import fr.gasser.daoexample.dao.Dao;
+import fr.gasser.daoexample.dao.DaoAbstractFactory;
+import fr.gasser.daoexample.model.Discipline;
+import fr.gasser.daoexample.model.Student;
+import fr.gasser.daoexample.model.Teacher;
+import fr.gasser.daoexample.dao.connection.ConnectionWrapper;
+import fr.gasser.daoexample.dao.connection.DummyConnectionWrapper;
+
+public class DaoFactory implements DaoAbstractFactory {
+    private static final ConnectionWrapper CONNECTION_WRAPPER = new DummyConnectionWrapper();
+
+    @Override
+    public Dao<Student> createStudentDao() {
+        return new StudentDao(DaoFactory.CONNECTION_WRAPPER);
+    }
+
+    @Override
+    public Dao<Teacher> createTeacherDao() {
+        return new TeacherDao(DaoFactory.CONNECTION_WRAPPER);
+    }
+
+    @Override
+    public Dao<Discipline> createDisciplineDao() {
+        return new DisciplineDao(DaoFactory.CONNECTION_WRAPPER);
+    }
+}
diff --git a/persistence/src/main/java/fr/gasser/daoexample/dao/DisciplineDao.java b/persistence/src/main/java/fr/gasser/daoexample/dao/dummy/DisciplineDao.java
similarity index 82%
rename from persistence/src/main/java/fr/gasser/daoexample/dao/DisciplineDao.java
rename to persistence/src/main/java/fr/gasser/daoexample/dao/dummy/DisciplineDao.java
index 9f7fb25..af85000 100644
--- a/persistence/src/main/java/fr/gasser/daoexample/dao/DisciplineDao.java
+++ b/persistence/src/main/java/fr/gasser/daoexample/dao/dummy/DisciplineDao.java
@@ -1,7 +1,8 @@
-package fr.gasser.daoexample.dao;
+package fr.gasser.daoexample.dao.dummy;
 
+import fr.gasser.daoexample.dao.Dao;
 import fr.gasser.daoexample.model.Discipline;
-import fr.gasser.daoexample.sql.Connection;
+import fr.gasser.daoexample.dao.connection.ConnectionWrapper;
 
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -16,8 +17,8 @@ public class DisciplineDao extends Dao<Discipline> {
             new Discipline(2, "Qsdf")
     ));
 
-    public DisciplineDao(Connection connection) {
-        super(connection);
+    public DisciplineDao(ConnectionWrapper connectionWrapper) {
+        super(connectionWrapper);
     }
 
     @Override
diff --git a/persistence/src/main/java/fr/gasser/daoexample/dao/FactoryType.java b/persistence/src/main/java/fr/gasser/daoexample/dao/dummy/FactoryType.java
similarity index 68%
rename from persistence/src/main/java/fr/gasser/daoexample/dao/FactoryType.java
rename to persistence/src/main/java/fr/gasser/daoexample/dao/dummy/FactoryType.java
index 008e26c..22e3300 100644
--- a/persistence/src/main/java/fr/gasser/daoexample/dao/FactoryType.java
+++ b/persistence/src/main/java/fr/gasser/daoexample/dao/dummy/FactoryType.java
@@ -1,4 +1,4 @@
-package fr.gasser.daoexample.dao;
+package fr.gasser.daoexample.dao.dummy;
 
 public enum FactoryType {
     DaoFactory,
diff --git a/persistence/src/main/java/fr/gasser/daoexample/dao/StudentDao.java b/persistence/src/main/java/fr/gasser/daoexample/dao/dummy/StudentDao.java
similarity index 82%
rename from persistence/src/main/java/fr/gasser/daoexample/dao/StudentDao.java
rename to persistence/src/main/java/fr/gasser/daoexample/dao/dummy/StudentDao.java
index 50fad64..321d559 100644
--- a/persistence/src/main/java/fr/gasser/daoexample/dao/StudentDao.java
+++ b/persistence/src/main/java/fr/gasser/daoexample/dao/dummy/StudentDao.java
@@ -1,7 +1,8 @@
-package fr.gasser.daoexample.dao;
+package fr.gasser.daoexample.dao.dummy;
 
+import fr.gasser.daoexample.dao.Dao;
 import fr.gasser.daoexample.model.Student;
-import fr.gasser.daoexample.sql.Connection;
+import fr.gasser.daoexample.dao.connection.ConnectionWrapper;
 
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -16,8 +17,8 @@ public class StudentDao extends Dao<Student> {
             new Student(2, "Qsdf", "Jklm"))
     );
 
-    StudentDao(Connection connection) {
-        super(connection);
+    StudentDao(ConnectionWrapper connectionWrapper) {
+        super(connectionWrapper);
     }
 
     @Override
diff --git a/persistence/src/main/java/fr/gasser/daoexample/dao/TeacherDao.java b/persistence/src/main/java/fr/gasser/daoexample/dao/dummy/TeacherDao.java
similarity index 82%
rename from persistence/src/main/java/fr/gasser/daoexample/dao/TeacherDao.java
rename to persistence/src/main/java/fr/gasser/daoexample/dao/dummy/TeacherDao.java
index 6e0d864..97948da 100644
--- a/persistence/src/main/java/fr/gasser/daoexample/dao/TeacherDao.java
+++ b/persistence/src/main/java/fr/gasser/daoexample/dao/dummy/TeacherDao.java
@@ -1,7 +1,8 @@
-package fr.gasser.daoexample.dao;
+package fr.gasser.daoexample.dao.dummy;
 
+import fr.gasser.daoexample.dao.Dao;
 import fr.gasser.daoexample.model.Teacher;
-import fr.gasser.daoexample.sql.Connection;
+import fr.gasser.daoexample.dao.connection.ConnectionWrapper;
 
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -16,8 +17,8 @@ public class TeacherDao extends Dao<Teacher> {
             new Teacher(2, "Sit", "Amet"))
     );
 
-    TeacherDao(Connection connection) {
-        super(connection);
+    TeacherDao(ConnectionWrapper connectionWrapper) {
+        super(connectionWrapper);
     }
 
     @Override
diff --git a/persistence/src/main/java/fr/gasser/daoexample/dao/SqliteDaoFactory.java b/persistence/src/main/java/fr/gasser/daoexample/dao/sqlite/SqliteDaoFactory.java
similarity index 58%
rename from persistence/src/main/java/fr/gasser/daoexample/dao/SqliteDaoFactory.java
rename to persistence/src/main/java/fr/gasser/daoexample/dao/sqlite/SqliteDaoFactory.java
index bba43a5..7a7140d 100644
--- a/persistence/src/main/java/fr/gasser/daoexample/dao/SqliteDaoFactory.java
+++ b/persistence/src/main/java/fr/gasser/daoexample/dao/sqlite/SqliteDaoFactory.java
@@ -1,14 +1,16 @@
-package fr.gasser.daoexample.dao;
+package fr.gasser.daoexample.dao.sqlite;
 
+import fr.gasser.daoexample.dao.Dao;
+import fr.gasser.daoexample.dao.DaoAbstractFactory;
 import fr.gasser.daoexample.model.Discipline;
 import fr.gasser.daoexample.model.Student;
 import fr.gasser.daoexample.model.Teacher;
-import fr.gasser.daoexample.sql.Connection;
-import fr.gasser.daoexample.sql.SQLiteConnection;
+import fr.gasser.daoexample.dao.connection.ConnectionWrapper;
+import fr.gasser.daoexample.dao.connection.SQLiteConnectionWrapper;
 
 public class SqliteDaoFactory implements DaoAbstractFactory {
 
-    private static Connection conn = new SQLiteConnection();
+    private static final ConnectionWrapper conn = new SQLiteConnectionWrapper();
 
     @Override
     public Dao<Student> createStudentDao() {
diff --git a/persistence/src/main/java/fr/gasser/daoexample/dao/StudentSQLiteDao.java b/persistence/src/main/java/fr/gasser/daoexample/dao/sqlite/StudentSQLiteDao.java
similarity index 76%
rename from persistence/src/main/java/fr/gasser/daoexample/dao/StudentSQLiteDao.java
rename to persistence/src/main/java/fr/gasser/daoexample/dao/sqlite/StudentSQLiteDao.java
index dfd957e..1478ec8 100644
--- a/persistence/src/main/java/fr/gasser/daoexample/dao/StudentSQLiteDao.java
+++ b/persistence/src/main/java/fr/gasser/daoexample/dao/sqlite/StudentSQLiteDao.java
@@ -1,7 +1,10 @@
-package fr.gasser.daoexample.dao;
+package fr.gasser.daoexample.dao.sqlite;
 
+import fr.gasser.daoexample.dao.Dao;
+import fr.gasser.daoexample.dao.DaoAbstractFactory;
+import fr.gasser.daoexample.dao.dummy.FactoryType;
 import fr.gasser.daoexample.model.Student;
-import fr.gasser.daoexample.sql.Connection;
+import fr.gasser.daoexample.dao.connection.ConnectionWrapper;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -16,18 +19,18 @@ public class StudentSQLiteDao extends Dao<Student> {
 
     private static final Logger LOGGER = LoggerFactory.getLogger(StudentSQLiteDao.class);
 
-    public StudentSQLiteDao(Connection connection) {
-        super(connection);
+    StudentSQLiteDao(ConnectionWrapper connectionWrapper) {
+        super(connectionWrapper);
         try {
-            connection.connect();
-            dropAndCreateTable(connection);
+            connectionWrapper.connect();
+            dropAndCreateTable(connectionWrapper);
         } catch (SQLException e) {
             LOGGER.error("Unable to connect to the database.", e);
         }
     }
 
-    private void dropAndCreateTable(Connection connection) throws SQLException {
-        try (Statement st = connection.getConnection().createStatement()) {
+    private void dropAndCreateTable(ConnectionWrapper connectionWrapper) throws SQLException {
+        try (Statement st = connectionWrapper.getConnection().createStatement()) {
             st.setQueryTimeout(30);  // set timeout to 30 sec.
             st.executeUpdate("DROP TABLE IF EXISTS students");
             // In SQLite, table rows normally have a 64-bit signed integer ROWID
@@ -41,7 +44,7 @@ public class StudentSQLiteDao extends Dao<Student> {
     @Override
     public boolean create(Student obj) {
         final String sql = "INSERT INTO students (name, surname) VALUES (?, ?)";
-        try (PreparedStatement st = connection.getConnection().prepareStatement(sql)) {
+        try (PreparedStatement st = connectionWrapper.getConnection().prepareStatement(sql)) {
             st.setObject(1, obj.getName());
             st.setObject(2, obj.getSurname());
             final int ret = st.executeUpdate();
@@ -55,7 +58,7 @@ public class StudentSQLiteDao extends Dao<Student> {
 
     @Override
     public Student find(int id) {
-        try (PreparedStatement st = connection.getConnection().prepareStatement("SELECT rowid,* FROM students WHERE rowid = ?")) {
+        try (PreparedStatement st = connectionWrapper.getConnection().prepareStatement("SELECT rowid,* FROM students WHERE rowid = ?")) {
             st.setObject(1, id);
             final ResultSet rs = st.executeQuery();
             final String name = rs.getString("name");
@@ -70,7 +73,7 @@ public class StudentSQLiteDao extends Dao<Student> {
     @Override
     public List<Student> findAll() {
         List<Student> results = new ArrayList<>();
-        try (Statement st = connection.getConnection().createStatement()) {
+        try (Statement st = connectionWrapper.getConnection().createStatement()) {
             ResultSet rs = st.executeQuery("select rowid,* from students");
             while (rs.next()) {
                 final int id = rs.getInt("rowid");
@@ -86,7 +89,7 @@ public class StudentSQLiteDao extends Dao<Student> {
 
     @Override
     public boolean update(Student obj) {
-        try (PreparedStatement st = connection.getConnection().prepareStatement("UPDATE students SET name = ?, surname = ?  WHERE rowid = ?")) {
+        try (PreparedStatement st = connectionWrapper.getConnection().prepareStatement("UPDATE students SET name = ?, surname = ?  WHERE rowid = ?")) {
             st.setString(1, obj.getName());
             st.setString(2, obj.getSurname());
             st.setInt(3, obj.getId());
@@ -101,7 +104,7 @@ public class StudentSQLiteDao extends Dao<Student> {
     @Override
     public boolean delete(Student obj) {
         String deleteSQL = "DELETE FROM students WHERE rowid = ?";
-        try (PreparedStatement st = connection.getConnection().prepareStatement(deleteSQL)) {
+        try (PreparedStatement st = connectionWrapper.getConnection().prepareStatement(deleteSQL)) {
             st.setInt(1, obj.getId());
             st.executeUpdate();
             return true;
@@ -114,7 +117,7 @@ public class StudentSQLiteDao extends Dao<Student> {
 
     /**
      * Quick testing of CRUD operations
-     * @param args
+     * TODO: write some unit tests
      */
     public static void main(String[] args) {
         DaoAbstractFactory df = DaoAbstractFactory.createFactory(FactoryType.SqliteDaoFactory);
diff --git a/persistence/src/main/java/fr/gasser/daoexample/model/Discipline.java b/persistence/src/main/java/fr/gasser/daoexample/model/Discipline.java
index 07eb89f..c708d3f 100644
--- a/persistence/src/main/java/fr/gasser/daoexample/model/Discipline.java
+++ b/persistence/src/main/java/fr/gasser/daoexample/model/Discipline.java
@@ -32,15 +32,15 @@ public class Discipline extends Entity {
         return teachers.add(teacher);
     }
 
-    public boolean removeTeacher(Object o) {
-        return teachers.remove(o);
+    public boolean removeTeacher(Teacher t) {
+        return teachers.remove(t);
     }
 
     public boolean addStudent(Student student) {
         return students.add(student);
     }
 
-    public boolean removeStudent(Object o) {
-        return students.remove(o);
+    public boolean removeStudent(Student s) {
+        return students.remove(s);
     }
 }
diff --git a/persistence/src/main/java/fr/gasser/daoexample/model/Entity.java b/persistence/src/main/java/fr/gasser/daoexample/model/Entity.java
index 0a18a26..6253bd1 100644
--- a/persistence/src/main/java/fr/gasser/daoexample/model/Entity.java
+++ b/persistence/src/main/java/fr/gasser/daoexample/model/Entity.java
@@ -2,9 +2,9 @@ package fr.gasser.daoexample.model;
 
 public class Entity {
 
-    protected int id;
+    int id;
 
-    public Entity(int id) {
+    Entity(int id) {
         this.id = id;
     }
 
diff --git a/persistence/src/main/java/fr/gasser/daoexample/model/Teacher.java b/persistence/src/main/java/fr/gasser/daoexample/model/Teacher.java
index 04f7f9f..34009b2 100644
--- a/persistence/src/main/java/fr/gasser/daoexample/model/Teacher.java
+++ b/persistence/src/main/java/fr/gasser/daoexample/model/Teacher.java
@@ -44,8 +44,8 @@ public class Teacher extends Entity {
         return disciplines.add(discipline);
     }
 
-    public boolean removeDiscipline(Object o) {
-        return disciplines.remove(o);
+    public boolean removeDiscipline(Discipline discipline) {
+        return disciplines.remove(discipline);
     }
 
 }