diff --git a/src/main/kotlin/fr/postgresjson/serializer/Serializer.kt b/src/main/kotlin/fr/postgresjson/Serializer.kt
similarity index 98%
rename from src/main/kotlin/fr/postgresjson/serializer/Serializer.kt
rename to src/main/kotlin/fr/postgresjson/Serializer.kt
index 2d88019..c2487f4 100644
--- a/src/main/kotlin/fr/postgresjson/serializer/Serializer.kt
+++ b/src/main/kotlin/fr/postgresjson/Serializer.kt
@@ -1,4 +1,4 @@
-package fr.postgresjson.serializer
+package fr.postgresjson
 
 import com.fasterxml.jackson.core.JsonParser
 import com.fasterxml.jackson.core.JsonProcessingException
diff --git a/src/main/kotlin/fr/postgresjson/connexion/Connection.kt b/src/main/kotlin/fr/postgresjson/connexion/Connection.kt
index 8ecc931..94780f0 100644
--- a/src/main/kotlin/fr/postgresjson/connexion/Connection.kt
+++ b/src/main/kotlin/fr/postgresjson/connexion/Connection.kt
@@ -3,8 +3,8 @@ package fr.postgresjson.connexion
 import com.github.jasync.sql.db.pool.ConnectionPool
 import com.github.jasync.sql.db.postgresql.PostgreSQLConnection
 import com.github.jasync.sql.db.postgresql.PostgreSQLConnectionBuilder
+import fr.postgresjson.Serializer
 import fr.postgresjson.entity.EntityI
-import fr.postgresjson.serializer.Serializer
 import java.io.File
 
 
diff --git a/src/main/kotlin/fr/postgresjson/entity/Entity.kt b/src/main/kotlin/fr/postgresjson/entity/Entity.kt
index 3dbbd42..4f9b132 100644
--- a/src/main/kotlin/fr/postgresjson/entity/Entity.kt
+++ b/src/main/kotlin/fr/postgresjson/entity/Entity.kt
@@ -1,16 +1,90 @@
 package fr.postgresjson.entity
 
+import org.joda.time.DateTime
 import java.util.*
 
+/* ID */
 interface EntityI<T> {
     var id: T?
 }
+
 abstract class Entity<T>(override var id: T? = null) : EntityI<T?>
 abstract class UuidEntity(override var id: UUID? = UUID.randomUUID()) : Entity<UUID?>(id)
 abstract class IdEntity(override var id: Int? = null) : Entity<Int?>(id)
 
+/* Version */
 interface EntityVersioning<T> {
     var version: T
 }
 
-interface EntityVersioningIncrement : EntityVersioning<Int>
+interface EntityVersioningIncrement : EntityVersioning<Int?>
+class EntityVersioningIncrementImp() : EntityVersioningIncrement {
+    override var version: Int? = null
+}
+
+interface EntityVersioningDate : EntityVersioning<DateTime?>
+class EntityVersioningDateImp() : EntityVersioningDate {
+    override var version: DateTime? = null
+}
+
+/* Dates */
+interface EntityCreatedAt {
+    var createdAt: DateTime?
+}
+
+interface EntityUpdatedAt {
+    var updatedAt: DateTime?
+}
+
+class EntityCreatedAtImp : EntityCreatedAt {
+    override var createdAt: DateTime? = null
+}
+
+class EntityUpdatedAtImp : EntityUpdatedAt {
+    override var updatedAt: DateTime? = null
+}
+
+interface User<T> : EntityI<T> {
+    fun isValid(): Boolean
+}
+
+/* Author */
+interface CreatedBy<T> {
+    var createdBy: User<T>?
+}
+
+interface UpdatedBy<T> {
+    var updatedBy: User<T>?
+}
+
+class EntityCreatedByImp<T> : CreatedBy<T> {
+    override var createdBy: User<T>? = null
+}
+
+class EntityUpdatedByImp<T> : UpdatedBy<T> {
+    override var updatedBy: User<T>? = null
+}
+
+/* Published */
+interface Published<UserT> {
+    var publishedAt: DateTime?
+    var publishedBy: User<UserT>?
+}
+
+class EntityPublishedImp<UserT> : Published<UserT> {
+    override var publishedAt: DateTime? = null
+    override var publishedBy: User<UserT>? = null
+}
+
+/* Implementation */
+abstract class EntityImp<T, UserT> : Entity<T>(),
+    EntityCreatedAt by EntityCreatedAtImp(),
+    EntityUpdatedAt by EntityUpdatedAtImp(),
+    CreatedBy<UserT> by EntityCreatedByImp(),
+    UpdatedBy<UserT> by EntityUpdatedByImp()
+
+abstract class EntityExtended<T, UserT> :
+    EntityImp<T, UserT>(),
+    EntityVersioningIncrement by EntityVersioningIncrementImp(),
+    Published<UserT> by EntityPublishedImp()
+
diff --git a/src/main/kotlin/fr/postgresjson/repository/Repository.kt b/src/main/kotlin/fr/postgresjson/repository/Repository.kt
index e876ce7..d4228ff 100644
--- a/src/main/kotlin/fr/postgresjson/repository/Repository.kt
+++ b/src/main/kotlin/fr/postgresjson/repository/Repository.kt
@@ -2,9 +2,9 @@ package fr.postgresjson.repository
 
 import com.github.jasync.sql.db.pool.ConnectionPool
 import com.github.jasync.sql.db.postgresql.PostgreSQLConnection
+import fr.postgresjson.Serializer
 import fr.postgresjson.entity.EntityCollection
 import fr.postgresjson.entity.EntityI
-import fr.postgresjson.serializer.Serializer
 
 interface RepositoryI<T, E : EntityI<T>>
 
diff --git a/src/test/kotlin/fr/postgresjson/serializer/ConnectionTest.kt b/src/test/kotlin/fr/postgresjson/ConnectionTest.kt
similarity index 98%
rename from src/test/kotlin/fr/postgresjson/serializer/ConnectionTest.kt
rename to src/test/kotlin/fr/postgresjson/ConnectionTest.kt
index d4f45a2..ece901e 100644
--- a/src/test/kotlin/fr/postgresjson/serializer/ConnectionTest.kt
+++ b/src/test/kotlin/fr/postgresjson/ConnectionTest.kt
@@ -1,4 +1,4 @@
-package fr.postgresjson.serializer
+package fr.postgresjson
 
 import fr.postgresjson.connexion.Connection
 import fr.postgresjson.entity.IdEntity
diff --git a/src/test/kotlin/fr/postgresjson/EntityTest.kt b/src/test/kotlin/fr/postgresjson/EntityTest.kt
new file mode 100644
index 0000000..074a26e
--- /dev/null
+++ b/src/test/kotlin/fr/postgresjson/EntityTest.kt
@@ -0,0 +1,25 @@
+package fr.postgresjson
+
+import fr.postgresjson.entity.*
+import org.junit.jupiter.api.Assertions.assertTrue
+import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.TestInstance
+
+@TestInstance(TestInstance.Lifecycle.PER_CLASS)
+class EntityTest() {
+    private class ObjTest(var name: String): EntityExtended<Int?, Int?>()
+
+    @Test
+    fun getObject() {
+        val obj: ObjTest? = ObjTest("plop")
+        assertTrue(obj is ObjTest)
+        assertTrue(obj is EntityExtended<Int?, Int?>)
+        assertTrue(obj is EntityI<Int?>)
+        assertTrue(obj is Entity<Int?>)
+        assertTrue(obj is Published<Int?>)
+        assertTrue(obj is CreatedBy<Int?>)
+        assertTrue(obj is UpdatedBy<Int?>)
+        assertTrue(obj is EntityCreatedAt)
+        assertTrue(obj is EntityUpdatedAt)
+    }
+}
\ No newline at end of file
diff --git a/src/test/kotlin/fr/postgresjson/serializer/RequestTest.kt b/src/test/kotlin/fr/postgresjson/RequestTest.kt
similarity index 94%
rename from src/test/kotlin/fr/postgresjson/serializer/RequestTest.kt
rename to src/test/kotlin/fr/postgresjson/RequestTest.kt
index c4d1a70..85cb30d 100644
--- a/src/test/kotlin/fr/postgresjson/serializer/RequestTest.kt
+++ b/src/test/kotlin/fr/postgresjson/RequestTest.kt
@@ -1,4 +1,4 @@
-package fr.postgresjson.serializer
+package fr.postgresjson
 
 import fr.postgresjson.connexion.Connection
 import fr.postgresjson.entity.IdEntity
diff --git a/src/test/kotlin/fr/postgresjson/serializer/SerializerTest.kt b/src/test/kotlin/fr/postgresjson/SerializerTest.kt
similarity index 98%
rename from src/test/kotlin/fr/postgresjson/serializer/SerializerTest.kt
rename to src/test/kotlin/fr/postgresjson/SerializerTest.kt
index ed1126d..d957375 100644
--- a/src/test/kotlin/fr/postgresjson/serializer/SerializerTest.kt
+++ b/src/test/kotlin/fr/postgresjson/SerializerTest.kt
@@ -1,4 +1,4 @@
-package fr.postgresjson.serializer
+package fr.postgresjson
 
 import fr.postgresjson.entity.IdEntity
 import org.junit.jupiter.api.Assertions.assertEquals