diff --git a/concept/database/database_concept.dia b/concept/database/database_concept.dia
index e6417e4..b82f213 100644
Binary files a/concept/database/database_concept.dia and b/concept/database/database_concept.dia differ
diff --git a/database/migrations/2018_09_07_090452_create_account_classes_table.php b/database/migrations/2018_09_07_090452_create_account_classes_table.php
index 753b324..0af1024 100644
--- a/database/migrations/2018_09_07_090452_create_account_classes_table.php
+++ b/database/migrations/2018_09_07_090452_create_account_classes_table.php
@@ -19,6 +19,9 @@ class CreateAccountClassesTable extends Migration
             // Name of the account class
             $table->string('name');
 
+            // Number of the class
+            $table->smallInteger('number')->unsigned()->unique();
+
             // The type of the account class.
             $table->integer('io_type')->unsigned();
             $table->foreign('io_type')->references('id')->on('i_o_types')