Used Defined Search in SAP PI7.31 Single Stack

Hi All,

I am trying to use User Defined Search... I am referring below link -

http://scn.sap.com/community/pi-and-soa-middleware/blog/2010/12/06/pixi-selecting-messages-using-the-content-of-the-message-in-sap-pi-73--teaser

I am not getting how to define SEARCH CRITERIA and PREFIXES... I have imported external definition.... What is XPATH how to take XPATH of imported external definition... WHat is prefix namespace and prefix value?

Regards,

Rashmi Joshi