You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: I am Shirley Green.

ASSISTANT: How can I assist you today?

USER: I want to travel from DFW to HOU. Can you book a flight ticket for me?

ASSISTANT: Sure, will you mention your travelling dates please?

USER: I want to fly in the flight on Dec 18 and Dec 20.

ASSISTANT: Do you have any specifications?

USER: I am looking for a direct flight.

ASSISTANT: Do you have any other preferences?

USER: I want to depart in evening time.

ASSISTANT: Please give me a moment.

USER: Ok.

ASSISTANT: Thanks for waiting, there is no reservation found under your preferable details.

USER: That's ok. Anyways, thank you for your help.

ASSISTANT: Welcome, have a great day.