diff --git a/dblayer.php b/dblayer.php
index d30bc91..e88a233 100644
--- a/dblayer.php
+++ b/dblayer.php
@@ -18,6 +18,7 @@ To use it, extends in your code this class, and define the attributes :
   );
 - protected $primary = "id" ; the primary key of the table (in text). Actually
   the dbLayer abstraction don't supports primary key on multiples columns
+- protected $unique = array ("column", array ("column1", "column2");)
 
 Optionnaly, you can add the 
 - protected $debug = TRUE : enable the debug on screen (NOT FOR PROD !!)
@@ -28,6 +29,7 @@ class dblayer extends PDO
 {
   protected $fields = array ();
   protected $primary = null;
+  protected $unique = null;
   protected $db = null;
   public $debug = FALSE;
   /** Return all the tables available in the database */
@@ -36,7 +38,8 @@ class dblayer extends PDO
     $driver = $this->getAttribute(PDO::ATTR_DRIVER_NAME);
     $rc = @include_once ("dbLayer".ucfirst ($driver).".php");
     if ($rc === FALSE)
-      throw new Exception ("dbLayer driver $driver not available");
+      throw new Exception (sprintf (_("dbLayer driver %s not available"),
+                                    $driver), 500);
   }
 
   // TODO !!
@@ -63,9 +66,14 @@ class dblayer extends PDO
   function create ($datas)
   {
     if ($this->db === null)
-      throw new Exception ("Database not connected");
+      throw new Exception (_("Database not connected"), 500);
+    if ($this->unique === null)
+      throw new Exception (_("Unique fields of table are not defined"), 500);
     if (!is_array ($datas))
-      throw new Exception ("The datas provided to create are not array");
+      throw new Exception (_("The datas provided to create are not array"),
+                           405);
+    if (!in_array ($this->primary, $this->unique))
+      $this->unique[] = $this->primary;
     $datasOK = array ();
     // Check for missing parameters
     foreach ($this->fields as $key=>$params)
@@ -73,12 +81,43 @@ class dblayer extends PDO
       if (in_array ("autoincrement", $params))
         $datas[$key] = null;
       if (in_array ("not null", $params) && !array_key_exists ($key, $datas))
-        throw new Exception ("Mandatory field '$key' not provided");
+        throw new Exception ("Mandatory field '$key' not provided", 405);
       // TODO : Check for type inconsistancies before create $datasOK
       if (array_key_exists ($key, $datas))
         $datasOK[$key] = $datas[$key];
     }
 
+    // Check if the unique constrain is valid before doing the insertion
+    foreach ($this->unique as $columns)
+    {
+      if (is_array ($columns))
+      {
+        $select = array ();
+        foreach ($columns as $col)
+        {
+          if (!array_key_exists ($col, $datasOK)) continue;
+          $select[] = array ($col, $datasOK[$col]);
+        }
+        $rc = $this->read ($select, array ($this->primary));
+        if (count ($rc) > 0)
+          throw new Exception (sprintf (
+                        _("The provided value for columns '%s' already exists"),
+                        implode (",", $columns)), 405);
+      }
+      else
+      {
+        if (!array_key_exists ($columns, $datasOK)) continue;
+        $rc = $this->read (array (array ($columns, $datasOK[$columns])),
+                           array ($this->primary));
+        if (count ($rc) > 0)
+          throw new Exception (sprintf (
+                         _("The provided value for column '%s' already exists"),
+                         $columns), 405);
+      }
+    }
+
+    // TODO : Check if the foreign keys constrains are valid before doing the
+    // insertion
     $req = "INSERT INTO `".$this->table."` ";
     $req .= "(".implode (",", array_keys ($datasOK)).")";
     $req .= " VALUES ";
@@ -97,7 +136,7 @@ class dblayer extends PDO
       elseif ($this->fields[$key][0] === "datetime")
         $st->bindValue (":$key", $val, PDO::PARAM_STR);
       else
-        throw new Exception ("TO BE DEVELOPPED : ".$this->fields[$key][0]);
+        throw new Exception ("TO BE DEVELOPPED : ".$this->fields[$key][0], 500);
     }
 
     $st->execute ();
@@ -116,13 +155,22 @@ class dblayer extends PDO
   function read ($select=null, $display=null, $order=null)
   {
     if ($this->db === null)
-      throw new Exception ("Database not connected");
+      throw new Exception (_("Database not connected"), 500);
+    if ($select !== null && !is_array ($select))
+      throw new Exception (_("Select information provided is not an array"),
+                           405);
+    if ($display !== null && !is_array ($display))
+      throw new Exception (_("Display information provided is not an array"),
+                           405);
+    if ($order !== null && !is_array ($order))
+      throw new Exception (_("Order information provided is not an array"),
+                           405);
     if ($display !== null)
     {
       foreach ($display as $f)
       {
         if (!in_array ($f, array_keys ($this->fields)))
-          throw new Exception ("Field $f not allowed");
+          throw new Exception (sprintf (_("Field %s not allowed"), $f), 506);
       }
     }
     $req = "SELECT ";
@@ -180,7 +228,7 @@ class dblayer extends PDO
   function update ($updatekey, $datas)
   {
     if ($this->db === null)
-      throw new Exception ("Database not connected");
+      throw new Exception (_("Database not connected"), 500);
     $datasOK = array ();
     // Check for missing parameters
     foreach ($this->fields as $key=>$params)
@@ -192,6 +240,36 @@ class dblayer extends PDO
     if (count ($datasOK) === 0)
       throw new Exception (_("Don't receive any field to display"), 501);
 
+    // Check if the unique constrain is valid before doing the insertion
+    foreach ($this->unique as $columns)
+    {
+      if (is_array ($columns))
+      {
+        $select = array ();
+        foreach ($columns as $col)
+        {
+          if (!array_key_exists ($col, $datasOK)) continue;
+          $select[] = array ($col, $datasOK[$col]);
+        }
+        $rc = $this->read ($select, array ($this->primary));
+        if (count ($rc) > 0)
+          throw new Exception (sprintf (
+                        _("The provided value for columns '%s' already exists"),
+                        implode (",", $columns)), 405);
+      }
+      else
+      {
+        if (!array_key_exists ($columns, $datasOK)) continue;
+        $rc = $this->read (array (array ($columns, $datasOK[$columns])),
+                           array ($this->primary));
+        if (count ($rc) > 0)
+          throw new Exception (sprintf (
+                         _("The provided value for column '%s' already exists"),
+                         $columns), 405);
+      }
+    }
+
+    // TODO : Check if the foreign keys constrains are valid before doing the
     $req = "UPDATE `".$this->table."` SET ";
     $i = 0;
     foreach ($datasOK as $key=>$val)
@@ -219,7 +297,7 @@ class dblayer extends PDO
       elseif ($this->fields[$key][0] === "datetime")
         $st->bindValue (":$key", $val, PDO::PARAM_STR);
       else
-        throw new Exception ("TO BE DEVELOPPED : ".$this->fields[$key][0]);
+        throw new Exception ("TO BE DEVELOPPED : ".$this->fields[$key][0], 500);
     }
 
     $st->execute ();
@@ -269,6 +347,7 @@ class zone extends dbLayer
     "closedate"=>array ("datetime"),
   );
   protected $primary = "id";
+  protected $unique = array ("id", array ("zone", "viewname"));
 }
 
 ini_set ("date.timezone", "Europe/Paris");