You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I aid you?

USER: My name is Mark Thompson. I have a plan to meet my friend in Oakland. Can you help me for booking a flight ticket?

ASSISTANT: Sure, can you please share your trip dates?

USER: My travelling dates are from 12/18 till 12/20.

ASSISTANT: Ok, may I know your airport codes?

USER: My travelling airport codes are from DTW to OAK.

ASSISTANT: Sorry, no flights are available on your route.

USER: That's ok, thank you for checking.

ASSISTANT: Welcome, have a nice day.