diff --git a/htdocs/install/mysql/migration/12.0.0-13.0.0.sql b/htdocs/install/mysql/migration/12.0.0-13.0.0.sql
index 17b58f278cf..934c8495d03 100644
--- a/htdocs/install/mysql/migration/12.0.0-13.0.0.sql
+++ b/htdocs/install/mysql/migration/12.0.0-13.0.0.sql
@@ -205,6 +205,7 @@ ALTER TABLE llx_recruitment_recruitmentcandidature_extrafields ADD INDEX idx_rec
 ALTER TABLE llx_recruitment_recruitmentcandidature ADD UNIQUE INDEX uk_recruitmentcandidature_email_msgid(email_msgid);
 
 
+ALTER TABLE llx_product_attribute ADD COLUMN ref_ext VARCHAR(255) after ref;
 
 
 CREATE TABLE llx_product_attribute_combination_price_level
diff --git a/htdocs/install/mysql/tables/llx_product_attribute.sql b/htdocs/install/mysql/tables/llx_product_attribute.sql
index f7ebee3cc23..c81d122d9bb 100644
--- a/htdocs/install/mysql/tables/llx_product_attribute.sql
+++ b/htdocs/install/mysql/tables/llx_product_attribute.sql
@@ -1,5 +1,6 @@
 -- ============================================================================
 -- Copyright (C) 2016      Marcos García         <marcosgdf@gmail.com>
+-- Copyright (C) 2020      Laurent Destailleur   <eldy@users.sourceforge.net>
 --
 -- This program is free software; you can redistribute it and/or modify
 -- it under the terms of the GNU General Public License as published by
@@ -14,12 +15,15 @@
 -- You should have received a copy of the GNU General Public License
 -- along with this program. If not, see <https://www.gnu.org/licenses/>.
 --
+-- llx_product_attribute is table for labels of product variants attributes. For exemple: COLOR, SIZE, ... 
+-- The different possible values (for example BLUE, GREEN, ... for COLOR) are defined into llx_product_attribute_value.
 -- ============================================================================
 
 CREATE TABLE llx_product_attribute
 (
   rowid INT PRIMARY KEY NOT NULL AUTO_INCREMENT,
   ref VARCHAR(255) NOT NULL,
+  ref_ext VARCHAR(255) NOT NULL,
   label VARCHAR(255) NOT NULL,
   rang INT DEFAULT 0 NOT NULL,
   entity INT DEFAULT 1 NOT NULL
diff --git a/htdocs/install/mysql/tables/llx_product_attribute_combination.sql b/htdocs/install/mysql/tables/llx_product_attribute_combination.sql
index a00b4009c72..041ffe5a60e 100644
--- a/htdocs/install/mysql/tables/llx_product_attribute_combination.sql
+++ b/htdocs/install/mysql/tables/llx_product_attribute_combination.sql
@@ -1,5 +1,6 @@
 -- ============================================================================
 -- Copyright (C) 2016      Marcos García         <marcosgdf@gmail.com>
+-- Copyright (C) 2020      Laurent Destailleur   <eldy@users.sourceforge.net>
 --
 -- This program is free software; you can redistribute it and/or modify
 -- it under the terms of the GNU General Public License as published by
@@ -14,7 +15,7 @@
 -- You should have received a copy of the GNU General Public License
 -- along with this program. If not, see <https://www.gnu.org/licenses/>.
 --
--- Table to store all product variants of a parent product
+-- Table to store links between a parent product and its variant products.
 -- ============================================================================
 
 CREATE TABLE llx_product_attribute_combination
diff --git a/htdocs/install/mysql/tables/llx_product_attribute_value.sql b/htdocs/install/mysql/tables/llx_product_attribute_value.sql
index c4e0ec91459..09e7d325d0d 100644
--- a/htdocs/install/mysql/tables/llx_product_attribute_value.sql
+++ b/htdocs/install/mysql/tables/llx_product_attribute_value.sql
@@ -15,6 +15,8 @@
 -- You should have received a copy of the GNU General Public License
 -- along with this program. If not, see <https://www.gnu.org/licenses/>.
 --
+-- llx_product_attribute_value is table for different available values of a product variants attributes.
+-- For example BLUE, GREEN, ... for the product attribute COLOR.
 -- ============================================================================
 
 CREATE TABLE llx_product_attribute_value