UML Event Tables: Differences between Event & Trigger, Intermidiate Responses

Suppose the event/use-case "Buy Online", in the event table, the entry may look like

• Event: Customer buys products online
• Trigger: Same as Event?
• Source: Customer
• Use Case: Buy Online
• Response: Confi开发者_运维百科rmation Code, Validate Credit Card
• Destination: Customer, Payment Verification System

If a Payment Verification System is called in the process to Validate Credit Card, do I include it? It isit the final response?

No, it is not the final response, but only a part of this use case.
The Validate Credit Card is an extension (not an include) of the main use case, as it is optional (there are other way to pay online).