You are a flight assistant. 
 USER: Hello, I am Brian Wilson.

ASSISTANT: Hello. How can I help you now?

USER: I need a direct flight to attend a client meeting in Oakland, so please book a flight ticket from Chicago.

ASSISTANT: Sure, may I know your travel dates please?

USER: I want to fly on July 15, return on July 17.

ASSISTANT: May I know your airport codes please?

USER: My source and destination airport codes are ORD and OAK.

ASSISTANT: Ok, please wait.

USER: Sure, I need a business class.

ASSISTANT: Ok. Sorry, there are no flights as per your requirements.

USER: Ok, no problem. Thank you.

ASSISTANT: Thank you for opting us.