You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: Debra Scott here.

ASSISTANT: Scott, how can I help you?

USER: I want to meet my niece at Houston, could you book my ticket from Dallas?

ASSISTANT: Sure, I will help you. Can you please tell me your source and destination airport codes?

USER: I will travel from DFW to HOU.

ASSISTANT: Ok, may I know trip dates?

USER: My trip dates are 07/18 and 07/20.

ASSISTANT: Please wait for a while.

USER: Ok.

ASSISTANT: Sorry Scott, there is no flight available on your preferred dates.

USER: No problem, thank you.

ASSISTANT: You are welcome and have a nice day.