To detect when a channel has received duplicate messages, you must:

• Create a VMD file containing a single default message definition that processes all messages.

• In this default message definition, define a Transformation Script that checks for duplicate messages.

• Use the Transform Window to specify that this VMD file performs scripted transformations.

	The message definition in the VMD file is specified to be the default message because it is assumed that you do not care what type of message appears - all you want to know is whether the message is a duplicate. For information on creating a default message definition for a VMD file, see Specifying Default Messages.

To create a Transformation Script for a message definition, go to the Chameleon Workspace menu, expand the message definition you want to define a script for, and double-click Transformation Script:

In this window, type the following simple Python script, which detects duplicate messages:

try:
    if value == LastMessage:
       print "ALERT - DUPLICATE TRANSACTION OCCURRED"
    LastMessage = value
except NameError:
    LastMessage = value

This script saves the last read message in a variable named LastMessage. When a new message arrives, it is compared to the message stored in LastMessage. If they are identical, the new message is a duplicate, and a warning message is printed.

After you have created the script, the final step is to modify the VMD file to indicate that it is performing scripted transformation. To do this:

• In the Chameleon toolbar, click Transform.
• In the Transformation window, select the Scripted Transformation radio button:

• From the File menu, select Save to save your VMD file.

Your VMD file is now ready for use.

Now that you have defined the VMD file that detects whether a duplicate message has been sent, the next step is to to update your Iguana channel to use this VMD file.

	A copy of this VMD file is available here: duplicatetest.vmd.