You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you today?

USER: Please help me to book a flight ticket from OAK to DTW.

ASSISTANT: Sure, may I know your name please?

USER: My name is Andrew Lopez.

ASSISTANT: Ok, may I know your travelling details?

USER: My trip dates are from Dec, 15 to Dec, 17.

ASSISTANT: Is there any specific class preference for you?

USER: I prefer business class.

ASSISTANT: Do you need any connections limit?

USER: I need a single connecting flight.

ASSISTANT: Do you have any other specifications please?

USER: No.

ASSISTANT: Sorry Lopez, there is no flight found as per your travelling details.

USER: No problem, thanks for your information.

ASSISTANT: You are welcome.