diff --git a/application/transaction.class.inc.php b/application/transaction.class.inc.php
new file mode 100644
index 000000000..ffc55c257
--- /dev/null
+++ b/application/transaction.class.inc.php
@@ -0,0 +1,111 @@
+<?php
+// Copyright (C) 2010 Combodo SARL
+//
+//   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
+//   the Free Software Foundation; version 3 of the License.
+//
+//   This program is distributed in the hope that it will be useful,
+//   but WITHOUT ANY WARRANTY; without even the implied warranty of
+//   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//   GNU General Public License for more details.
+//
+//   You should have received a copy of the GNU General Public License
+//   along with this program; if not, write to the Free Software
+//   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+
+/**
+ * This class records the pending "transactions" corresponding to forms that have not been
+ * submitted yet, in order to prevent double submissions. When created a transaction remains valid
+ * until it is "used" by calling IsTransactionValid once, or until it
+ * expires (delay = TRANSACTION_EXPIRATION_DELAY, defaults to 4 hours)
+ * @package     iTop
+ */
+// How long a "transaction" is considered valid, i.e. when a form is submitted
+// if the form dates back from too long a time, it is considered invalid. This is
+// because since HTTP is not a connected protocol, we cannot know when a user disconnects
+// from the application (maybe just by closing her browser), so we keep track - in the database - of all pending
+// forms that have not yet been submitted. To limit this list we consider that after some time
+// a "transaction" is no loger valid an gets purged from the table
+define ('TRANSACTION_EXPIRATION_DELAY', 3600*4); // default: 4h
+
+require_once('../core/dbobject.class.php');
+
+class privUITransaction extends DBObject
+{
+	public static function Init()
+	{
+		$aParams = array
+		(
+			"category" => "gui",
+			"key_type" => "autoincrement",
+			"key_label" => "",
+			"name_attcode" => "expiration_date",
+			"state_attcode" => "",
+			"reconc_keys" => array(),
+			"db_table" => "priv_transaction",
+			"db_key_field" => "id",
+			"db_finalclass_field" => "",
+		);
+		MetaModel::Init_Params($aParams);
+		MetaModel::Init_AddAttribute(new AttributeDateTime("expiration_date", array("allowed_values"=>null, "sql"=>"expiration_date", "default_value"=>"", "is_null_allowed"=>false, "depends_on"=>array())));
+
+		MetaModel::Init_SetZListItems('details', array('expiration_date')); // Attributes to be displayed for the complete details
+		MetaModel::Init_SetZListItems('list', array('expiration_date')); // Attributes to be displayed for a list
+	}
+	/**
+	 * Create a new transaction, store it in the database and return its id
+	 * @param void
+	 * @return int The identifier of the new transaction
+	 */
+	public static function GetNewTransactionId()
+	{
+		// First remove all the expired transactions...
+		self::CleanupExpiredTransactions();
+		$oTransaction = new privUITransaction();
+		$sDate = date('Y-m-d H:i:s', time()+TRANSACTION_EXPIRATION_DELAY);
+		$oTransaction->Set('expiration_date', $sDate); // 4 h delay by default
+		$oTransaction->DBInsert();
+		return sprintf("%d", $oTransaction->GetKey());
+	}
+
+	/**
+	 * Check whether a transaction is valid or not and remove the valid transaction from
+	 * the database so that another call to IsTransactionValid for the same transaction
+	 * will return false
+	 * @param int $id Identifier of the transaction, as returned by GetNewTransactionId
+	 * @return bool True if the transaction is valid, false otherwise
+	 */	
+	public static function IsTransactionValid($id)
+	{
+		// First remove all the expired transactions...
+		self::CleanupExpiredTransactions();
+		// TO DO put a critical section around this part to be 100% safe...
+		// sem_acquire(...)
+		$bResult  = false;
+		$oTransaction = MetaModel::GetObject('privUITransaction', $id, false /* MustBeFound */);
+		if ($oTransaction)
+		{
+			$bResult = true;
+			$oTransaction->DBDelete();
+		}
+		// sem_release(...)
+		return $bResult;
+	}
+
+	/**
+	 * Remove from the database all transactions that have expired
+	 */
+	protected static function CleanupExpiredTransactions()
+	{
+		$sQuery = 'SELECT privUITransaction WHERE expiration_date < NOW()';
+		$oSearch = DBObjectSearch::FromOQL($sQuery);
+		$oSet = new DBObjectSet($oSearch);
+		while($oTransaction = $oSet->Fetch())
+		{
+			$oTransaction->DBDelete();
+		}
+	}
+
+}
+?>
diff --git a/application/utils.inc.php b/application/utils.inc.php
index 490db8459..16de6f929 100644
--- a/application/utils.inc.php
+++ b/application/utils.inc.php
@@ -24,6 +24,7 @@
  */
 
 require_once('../core/config.class.inc.php');
+require_once('../application/transaction.class.inc.php');
 
 define('ITOP_CONFIG_FILE', '../config-itop.php');
 
@@ -31,6 +32,11 @@ class FileUploadException extends Exception
 {
 }
 
+
+/**
+ * Helper functions to interact with forms: read parameters, upload files...
+ * @package     iTop
+ */
 class utils
 {
 	private static $m_oConfig = null;
@@ -116,14 +122,12 @@ class utils
 	
 	public static function GetNewTransactionId()
 	{
-		// TO DO implement the real mechanism here
-		return sprintf("%08x", rand(0,2000000000));
+		return privUITransaction::GetNewTransactionId();
 	}
 	
 	public static function IsTransactionValid($sId)
 	{
-		// TO DO implement the real mechanism here
-		return true;
+		return privUITransaction::IsTransactionValid($sId);
 	}
 	
 	public static function ReadFromFile($sFileName)